Simple analog function generator (0.1Hz - 8MHz). Article reprinted from the site.
Among radio amateurs, the MAX038 microcircuit is deservedly popular, on the basis of which it is possible to assemble a simple function generator that covers the frequency band of 0.1 Hz - 20 MHz. Buying a MAX038 chip has become as easy as shelling pears, as indicated. The MAX038 clones that have appeared have very modest parameters compared to it. So, ICL8038 has a maximum operating frequency of 300 kHz, and XR2206 has a maximum operating frequency of 1 MHz. The circuits of simple analog function generators found in amateur radio literature also have a maximum frequency of several tens, and very rarely, hundreds of kHz.
An analog function generator circuit is proposed for your attention, which forms its signals of sinusoidal, rectangular, triangular shape and operates in the frequency range from 0.1 Hz to 8 MHz.
Front view:
Back view:
The generator has the following parameters:
output signal amplitude:
sinusoidal……………………………1.4 V;
rectangular……………………………..2.0 V;
triangular………………………………...2.0 V;
frequency ranges:
0.1…1 Hz;
1…10 Hz;
10…100 Hz;
100…1000 Hz;
1…10 kHz;
10…100 kHz;
100…1000 kHz;
1…10 MHz;
supply voltage………………………….220 V, 50 Hz.
The developed circuit of the function generator below was based on the circuit from:
The generator is made according to the classical scheme: integrator + comparator, only assembled on high-frequency components.
The integrator is based on the DA1 AD8038AR op amp with a bandwidth of 350 MHz and a slew rate of 425 V/µs. Comparator is made on DD1.1, DD1.2. Rectangular pulses from the output of the comparator (pin 6 DD1.2) are fed to the inverting input of the integrator. An emitter follower is made on VT1, from which triangular-shaped pulses are taken that control the comparator. The switch SA1 selects the required frequency range, the potentiometer R1 serves for smooth frequency adjustment. The trimmer resistor R15 sets the operating mode of the generator and regulates the amplitude of the triangular voltage. Trimmer resistor R17 regulates the constant component of the triangular voltage. From the emitter VT1, a triangular voltage is supplied to the switch SA2 and to the sinusoidal voltage driver, made on VT2, VD1, VD2. The trimmer resistor R6 sets the minimum distortion of the sinusoid, and the trimmer resistor R12 adjusts the symmetry of the sinusoidal voltage. In order to reduce the harmonic coefficient, the tops of the triangular signal are limited to the circuits VD3, R9, C14, C16 and VD4, R10, C15, C17. From the buffer DD1.4, rectangular pulses are taken. The signal selected by the SA2 switch is fed to the R19 potentiometer (amplitude), and from it to the DA5 output amplifier, made on the AD8038AR. On the elements R24, R25, SA3, an output voltage attenuator 1:1 / 1:10 is made.
The generator is powered by a classic transformer source with linear stabilizers generating +5V, ±6V and ±3V voltages.
To indicate the frequency of the generator, a part of the circuit from an already finished frequency meter was used, taken from:
On the transistor VT3, an amplifier-shaper of rectangular pulses is made, from the output of which the signal is fed to the input of the microcontroller DD2 PIC16F84A. MK is clocked from a quartz resonator ZQ1 at 4 MHz. The SB1 button selects the price of the least significant digit 10, 1 or 0.1 Hz and the corresponding measurement time 0.1, 1 and 10 sec. WH1602D-TMI-CT with white characters on a blue background was used as an indicator. True, the viewing angle of this indicator turned out to be 6:00, which did not correspond to its installation in a case with a viewing angle of 12:00. But this trouble has been eliminated, as will be described below. Resistor R31 sets the backlight current, and resistor R28 adjusts the optimal contrast. It should be noted that the program for MK was written by the author for indicators of the type DV-16210, DV-16230, DV-16236, DV-16244, DV-16252 from DataVision, in which the initial initialization procedure apparently does not fit the WH1602 indicators from WinStar . As a result, after assembling the frequency meter, nothing was displayed on the indicator. There were no other small-sized indicators on sale at that time, so we had to make changes to the source code of the frequency meter program. Along the way, during the experiments, such a combination was revealed in the initialization procedure, in which a two-line display with a viewing angle of 6:00 became a single-line display, moreover, it was quite comfortable to read at a viewing angle of 12:00. The inscriptions displayed on the bottom line, hints about the mode of operation of the frequency meter, are no longer visible, but they are not particularly needed, because. additional functions of this frequency counter are not used.
Structurally, the functional generator is made on a printed circuit board made of one-sided foil fiberglass with dimensions of 110x133 mm, designed for a standard Z4 plastic case. The indicator is mounted vertically on the chamber on two corners. It is connected to the main board using a cable with a connector for IDC-16. A thin shielded cable is used to connect high-frequency circuits in the circuit. Here is a photo of the generator with the top case cover removed:
After the generator is turned on for the first time, it is necessary to control the supply voltages, and also set the -3V voltage at the DA7 LM337L output with a trimming resistor R29. Resistor R28 sets the optimal contrast of the indicator. To set up the generator, you need to connect an oscilloscope to its output, set the SA3 switch to the 1:1 position, SA2 to the position corresponding to the triangular voltage, SA1 to the 100 ... 1000 Hz position. Resistor R15 achieve stable signal generation. By moving the slider of the resistor R1 to the lower position according to the diagram, the trimming resistor R17 achieves the symmetry of the triangular signal relative to zero. Next, switch SA2 must be moved to the position corresponding to the sinusoidal form of the output signal, and trimming resistors R12 and R6, respectively, achieve symmetry and minimal distortion of the sinusoid.
Here's what happened in the end:
Square wave 1 MHz: Square wave 4 MHz: Triangle 1 MHz:
Triangle 1 MHz: Sine 8 MHz:
It should be noted that at frequencies above 4 MHz, distortions begin to be observed on the triangular and rectangular signals associated with insufficient bandwidth of the output amplifier. If desired, this disadvantage can be easily eliminated by transferring the output stage amplifier DA5 to the circuit from the source VT2 to SA2, i.e. use it as a sinusoidal signal amplifier, and instead of the output amplifier, use a repeater on another AD8038AR op amp, recalculating the resistance of the triangular (R18, R36) and rectangular (R21, R35) signal dividers to a smaller division factor, respectively.
Files:
Literature:
1) Wide range function generator. A.Ishutinov. Radio No. 1/1987
2) Economical multifunctional frequency meter. A. Sharypov. Radio No. 10-2002.
Low frequencies are designed to obtain periodic low-frequency electrical signals with specified parameters (shape, amplitude, signal frequency) at the output of the device.
KR1446UD1 (Fig. 35.1) is a general-purpose dual op-amp. Based on this microcircuit, devices for various purposes can be created, in particular, electrical oscillations, which are shown in Fig. 35.2-35.4. (Fig. 35.2):
♦ simultaneously and synchronously generates rectangular and sawtooth voltage pulses;
♦ has a single artificial middle point for both op amps, formed by the voltage divider R1 and R2 .
Built on the first of the op-amps, on the second - Schmitt with a wide hysteresis loop (U raCT \u003d U nHT; R3 / R5), accurate and stable switching thresholds. The generation frequency is determined by the formula:
f =———– and amounts to 265 Gi for the denominations indicated on the diagram. WITH
Rice. 35.7. Pinout and composition of the microcircuit KR 7446UD7
Rice. 35.2. generator of rectangular-triangular pulses on the chip KR1446UD 7
by changing the supply voltage from 2.5 to 7 V, this frequency changes by no more than 1%.
The improved one (Fig. 35.3) generates rectangular pulses, and their frequency depends on the value of the control
Rice. 35.3. controlled square wave generator
input voltage according to the law
When it changes
input voltage from 0.1 to 3 V, the generation frequency increases linearly from 0.2 to 6 kHz.
The generation frequency of the rectangular pulse generator on the KR1446UD5 microcircuit (Fig. 35.4) is linear in the value of the applied control voltage and at R6 = R7 is determined as:
5 V generation frequency increases linearly from 0 to 3700 Hz.
Rice. 35.4. voltage controlled generator
So, when the input voltage changes from 0.1 to
Based on TDA7233D microcircuits, using the base element as a single basis, fig. 35.5, a, you can collect sufficiently powerful pulses (), as well as voltages, fig. 35.5.
The generator (Fig. 35.5, 6, top) operates at a frequency of 1 kHz, which is determined by the selection of the elements Rl, R2, Cl, C2. The capacitance of the transition capacitor C sets the timbre and volume of the signal.
The generator (Fig. 35.5, b, bottom), produces a two-tone signal, subject to the individual selection of the capacitance of the capacitor C1 in each of the basic elements used, for example, 1000 and 1500 pF.
Voltages (Fig. 35.5, c) operate at a frequency of about 13 kHz (capacitor C1 is reduced to 100 pF):
♦ upper - generates negative gel voltage relative to the common bus;
♦ medium - produces a positive doubled relative to the supply voltage;
♦ lower - generates, depending on the transformation ratio, a bipolar equal voltage with galvanic (if necessary) isolation from the power source.
Rice. 35.5. abnormal use of TDA7233D microcircuits: a - basic element; b - as pulse generators; c - as voltage converters
When assembling converters, it should be taken into account that a significant part of the output voltage is lost on the rectifier diodes. In this regard, it is recommended to use Schottky as VD1, VD2. The load current of transformerless converters can reach 100-150 mA.
Rectangular pulses (Fig. 35.6) operate in the frequency range 60-600 Hz \ 0.06-6 kHz; 0.6-60 kHz. To correct the shape of the generated signals, a chain can be used (lower part of Fig. 35.6), connected to points A and B of the device.
Having covered the op-amp with positive feedback, it is easy to transfer the device to the mode of generating rectangular pulses (Fig. 35.7).
Variable frequency pulses (Fig. 35.8) can be made on the basis of the DA1 chip. When used as DA1 1/4 microcircuit LM339 by adjusting the potentiometer R3, the operating frequency is tuned within 740-2700 Hz (the value of capacitance C1 is not indicated in the original source). The initial generation frequency is determined by the product C1R6.
Rice. 35.8. wide-range tunable oscillator based on comparator
Rice. 35.7. generator of rectangular pulses at a frequency of 200 Hz
Rice. 35.6. LF square-wave generator
On the basis of comparators such as LM139, LM193 and the like, the following can be assembled:
♦ rectangular pulses with quartz stabilization (Fig. 35.9);
♦ pulses with electronic tuning.
Frequency-stable oscillations or the so-called “hourly” rectangular pulses can be performed on the DAI LTC1441 comparator (or similar) according to the typical circuit shown in fig. 35.10. The generation frequency is set by a quartz resonator Z1 and is 32768 Hz. When using a line of frequency dividers by 2, rectangular pulses with a frequency of 1 Hz are obtained at the output of the dividers. Within a small range, the operating frequency of the generator can be lowered by connecting a small capacity resonator in parallel.
Typically, LC and RC- are used in electronic devices. Less known are LR-, although devices with inductive sensors can be created on their basis,
Rice. 35.11. LR generator
Rice. 35.9. pulse generator on the comparator LM 7 93
Rice. 35.10. "clock" pulse generator
Detectors for wiring, pulses, etc.
On fig. 35.11 shows a simple LR square-wave generator operating in the frequency range 100 Hz - 10 kHz. As inductance and for sound
the generator operation is controlled by a telephone capsule TK-67. Frequency tuning is carried out by potentiometer R3.
Operable when the supply voltage changes from 3 to 12.6 V. When the supply voltage drops from 6 to 3-2.5 V, the upper generation frequency rises from 10-11 kHz to 30-60 kHz.
Note.
The range of generated frequencies can be extended to 7-1.3 MHz (for a microcircuit) by replacing the telephone capsule and resistor R5 with an inductor. In this case, when the diode limiter is turned off, signals close to a sinusoid can be obtained at the output of the device. The stability of the generation frequency of the device is comparable to the stability of RC generators.
Sound signals (Fig. 35.12) can be performed K538UNZ. To do this, it is enough to connect the input and output of the microcircuit with a capacitor or its analogue - a piezoceramic capsule. In the latter case, the capsule also acts as a sound emitter.
The generation frequency can be changed by selecting the capacitance of the capacitor. In parallel or in series, a piezoceramic capsule can be switched on to select the optimal generation frequency. The supply voltage of the generators is 6-9 V.
Rice. 35.72. audio frequencies on a chip
For an express check of the OS, the generator of sound signals, shown in Fig. 1, can be used. 35.13. The tested DA1 chip of type , or others with a similar pinout, is inserted into the socket, after which the power is turned on. If it is in good condition, the HA1 piezoceramic capsule emits a sound signal.
Rice. 35.13. sound generator - OS tester
Rice. 35.14. generator of rectangular pulses on OUKR1438UN2
Rice. 35.15. generator of sinusoidal signals on OUKR1438UN2
Rectangular signals at a frequency of 1 kHz, made on the KR1438UN2 chip, are shown in fig. 35.14. amplitude-stabilized sinusoidal signals at a frequency of 1 kHz is shown in fig. 35.15.
The generator that generates sinusoidal signals is shown in fig. 35.16. This one works in the frequency range of 1600-5800 Hz, although at frequencies above 3 kHz, the waveform is increasingly far from ideal, and the output signal amplitude drops by 40%. With a tenfold increase in the capacitances of capacitors C1 and C2, the tuning band of the generator, while maintaining the sinusoidal waveform, decreases to 170-640 Hz with an amplitude unevenness of up to 10%.
Rice. 35.7 7. generator of sinusoidal oscillations at a frequency of 400 Hz
Low-frequency generators (LFGs) are used to obtain undamped periodic oscillations of electric current in the frequency range from fractions of a Hz to tens of kHz. Such generators, as a rule, are amplifiers covered by positive feedback (Fig. 11.7,11.8) through phase-shifting chains. To implement this connection and to excite the generator, the following conditions are necessary: the signal from the output of the amplifier must be fed to the input with a phase shift of 360 degrees (or a multiple of it, i.e. 0, 720, 1080, etc. degrees), and itself the amplifier must have some gain margin, KycMIN. Since the condition for the optimal phase shift for the occurrence of generation can be satisfied only at one frequency, it is at this frequency that the amplifier with positive feedback is excited.
To shift the signal in phase, RC and LC circuits are used, in addition, the amplifier itself introduces a phase shift into the signal. To obtain positive feedback in the generators (Fig. 11.1, 11.7, 11.9), a double T-shaped RC bridge was used; in generators (Fig. 11.2, 11.8, 11.10) - Wien's bridge; in generators (Fig. 11.3 - 11.6, 11.11 - 11.15) - phase-shifting RC chains. In generators with RC chains, the number of links can be quite large. In practice, to simplify the scheme, the number does not exceed two or three.
Calculation formulas and ratios for determining the main characteristics of RC-generators of sinusoidal signals are given in Table 11.1. For ease of calculation and simplification of the selection of parts, elements with the same ratings were used. To calculate the generation frequency (in Hz), the values of resistance expressed in Ohms are substituted into the formulas, and capacitances - in Farads. For example, let's determine the generation frequency of an RC oscillator using a three-link RC positive feedback circuit (Fig. 11.5). At R \u003d 8.2 kOhm; C \u003d 5100 pF (5.1x1SG9 F) the operating frequency of the generator will be equal to 9326 Hz.
Table 11.1
In order for the ratio of the resistive-capacitive elements of the generators to correspond to the calculated values, it is highly desirable that the input and output circuits of the amplifier covered by the positive feedback loop do not shunt these elements and do not affect their value. In this regard, to build generator circuits, it is advisable to use amplification stages with high input and low output resistance.
On fig. 11.7, 11.9 shows the "theoretical" and simple practical schemes of generators using a double T-bridge in a positive feedback circuit.
Wien bridge generators are shown in fig. 11.8, 11.10 [R 1/88-34]. A two-stage amplifier was used as a ULF. The amplitude of the output signal can be adjusted with potentiometer R6. If you want to create a generator with a Wien bridge, tunable in frequency, in series with resistors R1, R2 (Fig. 11.2, 11.8) include a dual potentiometer. The frequency of such a generator can also be controlled by replacing the capacitors C1 and C2 (Fig. 11.2, 11.8) with a double variable capacitor. Since the maximum capacitance of such a capacitor rarely exceeds 500 pF, it is possible to tune the generation frequency only in the region of sufficiently high frequencies (tens, hundreds of kHz). The generation frequency stability in this range is low.
In practice, to change the generation frequency of such devices, switched sets of capacitors or resistors are often used, and field-effect transistors are used in the input circuits. In all the above circuits, there are no output voltage stabilization elements (for simplicity), although for generators operating at the same frequency or in a narrow range of its tuning, their use is not necessary.
Sinusoidal signal generator circuits using three-link phase-shifting RC chains (Fig. 11.3)
shown in fig. 11.11, 11.12. The generator (Fig. 11.11) operates at a frequency of 400 Hz [R 4/80-43]. Each of the elements of a three-link phase-shifting RC chain introduces a phase shift of 60 degrees, with a four-link - 45 degrees. A single-stage amplifier (Fig. 11.12), made according to the scheme with a common emitter, introduces a phase shift of 180 degrees necessary for the generation to occur. Note that the generator according to the circuit in Fig. 11.12 is operable when using a transistor with a high current transfer ratio (usually over 45 ... 60). With a significant decrease in the supply voltage and a non-optimal choice of elements for setting the transistor mode for direct current, the generation will fail.
Sound generators (Fig. 11.13 - 11.15) are similar in construction to generators with phase-shifting RC chains [Рl 10/96-27]. However, due to the use of inductance (telephone capsule TK-67 or TM-2V) instead of one of the resistive elements of the phase-shifting chain, they work with a smaller number of elements and in a larger range of supply voltage changes.
So, the sound generator (Fig. 11.13) is operational when the supply voltage changes within 1 ... 15 V (current consumption 2 ... 60 mA). In this case, the generation frequency changes from 1 kHz (upit = 1.5 V) to 1.3 kHz at 15 V.
Sound indicator with external control (fig. 11.14) also works at 1) supply=1...15 V; the generator is turned on / off by applying logic levels of one / zero to its input, which should also be within 1 ... 15 V.
The sound generator can also be made according to another scheme (Fig. 11.15). The frequency of its generation varies from 740 Hz (consumption current 1.2 mA, supply voltage 1.5 V) to 3.3 kHz (6.2 mA and 15 V). The generation frequency is more stable when the supply voltage changes within 3 ... 11 V - it is 1.7 kHz ± 1%. In fact, this generator is no longer made on RC, but on LC elements, moreover, the winding of a telephone capsule is used as an inductance.
The low-frequency generator of sinusoidal oscillations (Fig. 11.16) is assembled according to the "capacitive three-point" scheme characteristic of LC generators. The difference lies in the fact that the coil of a telephone capsule is used as an inductance, and the resonant frequency is in the range of sound vibrations due to the selection of capacitive circuit elements.
Another low-frequency LC-oscillator, made according to the cascode scheme, is shown in Fig. 11.17 [R 1/88-51]. As an inductance, you can use a universal or erasing heads from tape recorders, windings of chokes or transformers.
The RC generator (Fig. 11.18) is implemented on field-effect transistors [Рl 10/96-27]. A similar scheme is usually used in the construction of highly stable LC oscillators. Generation already occurs at a supply voltage exceeding 1 V. When the voltage changes from 2 to 10 6, the generation frequency decreases from 1.1 kHz to 660 Hz, and the current consumption increases, respectively, from 4 to 11 mA. Pulses with a frequency from units of Hz to 70 kHz and higher can be obtained by changing the capacitance of the capacitor C1 (from 150 pF to 10 μF) and the resistance of the resistor R2.
The sound generators presented above can be used as economical status indicators (on/off) of components and blocks of radio electronic equipment, in particular, light emitting diodes, for replacing or duplicating light indication, for emergency and alarm indication, etc.
Literature: Shustov M.A. Practical Circuitry (Book 1), 2003
This low-frequency harmonic sinusoidal signal generator circuit is designed for tuning and repairing audio frequency amplifiers.
Sine Wave Generator together with a millivoltmeter, an oscilloscope or a distortion meter, it creates a valuable complex for tuning and repairing all stages of an audio frequency amplifier.
Main characteristics:
- Generated frequencies: 300Hz, 1kHz, 3kHz.
- Maximum Harmonic Distortion (THD): 0.11% - 1kHz, 0.23% - 300Hz, 0.05% - 3kHz
- Current consumption: 4.5 mA
- Output voltage selection: 0 - 77.5 mV, 0 - 0.775 V.
The sinusoidal generator circuit is quite simple and is built on two transistors, which provide high frequency and amplitude stability. The oscillator design does not require any stabilization elements such as tubes, thermistors, or other special amplitude limiting components.
Each of the three frequencies (300 Hz, 1 kHz and 3 kHz) is set by switch S1. The amplitude of the output signal can be smoothly changed by means of a variable resistor R15 in two ranges, which are set by switch S2. Available amplitude ranges: 0 - 77.5 mV (219.7 mV pk-pk) and 0 - 0.775 V (2.191 V pk-pk).
The following figures show the layout of the printed circuit board and the location of the elements on it.
List of required radio components:
- R1-12k
- R2-2k2
- R3, R4, R5, R15 - 1k variable
- R6, R7 - 1K5
- R8-1k
- R9-4k7
- R10-3k3
- R11-2k7
- R12-300
- R13-100k
- C1 - 22n
- C2 - 3u3
- C3 - 330n
- C4 - 56n
- C5 - 330n
- C6, C7 - 100n
- D1, D2 - 1N4148
- T1, T2, T3 - BC337
- IO1-78L05
If all parts are installed correctly and there are no errors in the installation, the sinusoidal signal generator should work the first time it is turned on.
The supply voltage of the circuit can be in the range of 8-15 volts. To maintain a stable amplitude of the output signal voltage, the power line is additionally stabilized by the 78L05 microcircuit and diodes D1, D2, as a result, the output of the stabilizer is about 6.2 volts.
Before turning on for the first time, you must connect the generator output to a frequency meter or oscilloscope and use trimmer resistors R3, R4 and R5 to set the exact output frequency for each of the ranges: 300 Hz, 1 kHz and 3 kHz. If necessary, if it is not entirely possible to adjust the frequencies, then you can additionally select the resistance of constant resistors R6-R8.
http://pandatron.cz/?1134&sinusovy_generator_s_nizkym_zkreslenim
Continuing the topic of electronic designers, this time I want to talk about one of the devices for replenishing the arsenal of measuring instruments for a beginner radio amateur.
True, this device cannot be called a measuring device, but the fact that it helps in measurements is unequivocal.
Quite often, a radio amateur, and not only, has to face the need to check various electronic devices. This happens both at the debugging stage and at the repair stage.
To check, it may be necessary to trace the passage of a signal through different circuits of the device, but the device itself does not always allow this to be done without external signal sources.
For example, when setting up / checking a multi-stage low-frequency power amplifier.
To begin with, it is worth explaining a little about what will be discussed in this review.
I want to tell you about the constructor, which allows you to assemble a signal generator.
Generators are different, for example below are also generators :) 
But we will collect the signal generator. I've been using an old analog oscillator for many years. In terms of generating sinusoidal signals, it is very good, the frequency range is 10-100000 Hz, but it has large dimensions and cannot produce signals of other forms.
In this case, we will collect the DDS signal generator.
DDS is or in Russian - direct digital synthesis scheme.
This device can generate arbitrary waveforms and frequencies using an internal oscillator with a single frequency as a master.
The advantages of this type of generators are that it is possible to have a large tuning range with a very fine step and, if necessary, to be able to generate signals of complex shapes.
As always, first, a little about the packaging.
In addition to the standard packaging, the designer was packed in a white tight envelope.
All the components themselves were in an antistatic bag with a latch (quite a useful thing for a radio amateur :)) 
Inside the package, the components were just a mound, and when unpacked, they looked something like this. 
The display was wrapped in pimply polyethylene. About a year ago, I already made such a display using it, so I won’t dwell on it, I can only say that it arrived without incident.
The kit also included two BNC connectors, but of a simpler design than in the oscilloscope review. 
Separately, on a small piece of polyethylene foam, there were microcircuits and panels for them.
The device uses an ATmega16 microcontroller from Atmel.
Sometimes people confuse the names, calling the microcontroller a processor. In fact, these are different things.
The processor is essentially just a computer, the microcontroller contains, in addition to the processor, RAM and ROM, and various peripheral devices, DAC, ADC, PWM controller, comparators, etc. can also be present.
The second chip is the Dual Operational Amplifier LM358. The most common, massive, operational amplifier. 
First, let's unpack the whole set and see what they gave us.
Printed circuit board
Display 1602
Two BNC connectors
Two variable resistors and one trimmer
Quartz resonator
Resistors and Capacitors
Microcircuits
six buttons
Various connectors and fasteners 
Printed circuit board with double-sided printing, element markings on the top side.
Since the circuit diagram is not included in the kit, the board is marked not with the positional designations of the elements, but with their ratings. Those. everything can be assembled without a scheme. 
The metallization is done with high quality, I didn’t have any comments, the coating of the contact pads is excellent, it is easy to solder. 
The transitions between the sides of the print are made double.
Why it is done this way, and not as usual, I do not know, but it only adds reliability. 
First, on the printed circuit board, I began to draw a circuit diagram. But already in the process of work, I thought that some already known scheme was probably used when creating this constructor.
So it turned out, a search on the Internet brought me to this device.
By the link you can find a diagram, a printed circuit board and source codes with firmware.
But I still decided to draw the diagram exactly as it is and I can say that it is 100% consistent with the original version. The designers of the designer simply developed their own version of the printed circuit board. This means that if there are alternative firmware for this device, then they will work here too.
There is a note to the circuitry, the HS output is taken directly from the processor output, there are no protections, therefore there is a chance to accidentally burn this output :( 
Since I’m telling you, it’s worth describing the functional units of this circuit and describing some of them in more detail.
I made a color version of the circuit diagram, on which I highlighted the main nodes with color.
It's hard for me to choose the names of the colors, then I will describe as best I can :)
Purple on the left - the node of the initial reset and forced using the button.
When power is applied, the capacitor C1 is discharged, due to which the Reset pin of the processor will be low, as the capacitor charges through the resistor R14, the voltage at the Reset input will rise and the processor will start working.
Green - Buttons for switching operating modes
Light purple? - Display 1602, backlight current limiting resistor and contrast trimmer.
Red - the node of the signal amplifier and zero offset adjustment (toward the end of the review it is shown what it does)
Blue - DAC. Digital to Analog Converter. The DAC was assembled according to the scheme, this is one of the simplest DAC options. In this case, 8 bits of the DAC are used, since all the pins of one port of the microcontroller are used. By changing the code on the processor pins, you can get 256 voltage levels (8 bits). This DAC consists of a set of resistors of two ratings that differ from each other by 2 times, hence the name, consisting of two parts R and 2R.
The advantages of this solution are high speed at a penny cost, it is better to use accurate resistors. My friend and I used this principle, but for the ADC, the choice of exact resistors was small, so we used a slightly different principle, put all the resistors of the same rating, but where 2R was needed, we used 2 resistors connected in series.
Such a principle of digital-to-analog conversion was in one of the first "sound cards" -. There was also an R2R matrix connected to the LPT port.
As I wrote above, in this designer the DAC has a resolution of 8 bits, or 256 signal levels, this is more than enough for a simple device. 
On the author's page, in addition to the scheme, firmware, etc. found a block diagram of this device.
According to it, a more understandable connection of nodes. 
With the main part of the description finished, the extended one will be further in the text, and we will go directly to the assembly.
As in the previous examples, I decided to start with resistors.
There are a lot of resistors in this constructor, but there are only a few ratings.
The main number of resistors have only two ratings, 20k and 10k, and almost all are involved in the R2R matrix.
To make assembly a little easier, I’ll say that you don’t even have to determine their resistance, just 20k resistors 9 pieces, and 10k resistors, respectively 8 :) 
This time I used a slightly different mounting technology. I like it less than the previous ones, but also has the right to life. This technology in some cases speeds up installation, especially on a large number of identical elements.
In this case, the conclusions of the resistors are formed in the same way as before, after which all resistors of the same rating are installed on the board first, then the second, two such lines of components are obtained. 
On the reverse side, the pins are slightly bent, but not much, the main thing is that the elements do not fall out, and the board is placed on the table with the pins up. 
Then we take the solder in one hand, the soldering iron in the other and solder all the filled pads.
You shouldn’t be too zealous with the number of components, because if you stuff the entire board at once, then you can get lost in this “forest” :) 
At the end, we bite the protruding leads of the components right next to the solder. Side cutters can capture several leads at once (4-5-6 pieces at a time).
Personally, I don’t really welcome this mounting method and showed it just for the sake of demonstrating various assembly options.
Of the disadvantages of this method:
After trimming, sharp protruding tips are obtained
If the components are not in a row, then it is easy to get a mess from the conclusions, where everything starts to get confused and this only slows down the work.
Of the advantages:
High speed of assembly of the same type of components installed in one or two rows
Since the leads do not bend much, the dismantling of the component is facilitated.
This method of installation can often be found in cheap computer power supplies, although the conclusions are not bitten there, but cut off with something like a cutting disc. 
After installing the main number of resistors, we will have several pieces of different denominations left.
It’s clear with a pair, these are two 100k resistors.
The last three resistors are -
brown - red - black - red - brown - 12k
red - red - black - black - brown - 220 Ohm.
brown - black - black - black - brown - 100 Ohm. 
We solder the last resistors, the board after that should look something like this. 
Color-coded resistors are a good thing, but sometimes there is confusion about where to start marking from.
And if there are usually no problems with resistors where the marking consists of four stripes, since the last strip is often either silver or gold, then problems may arise with resistors where the marking consists of five stripes.
The fact is that the last stripe can have the same color as the stripes denoting the denomination.
To make it easier to recognize the markings, the last strip should stand apart from the rest, but this is ideal. In real life, everything happens not at all as it was intended, and the strips go in a row at the same distance from each other.
Unfortunately, in this case, either a multimeter can help, or just logic (in the case of assembling a device from a kit), when all known denominations are simply removed, and from the rest you can understand what kind of denomination is in front of us.
For example, a couple of photo options for marking resistors in this set.
1. Two neighboring resistors got a “mirror” marking, where it doesn’t matter where to read the value :)
2. Resistors for 100k, it can be seen that the last strip is a little further from the main ones (in both photos, the value is read from left to right). 
Okay, we are done with resistors and their marking difficulties, let's move on to simpler things.
There are only four capacitors in this set, while they are paired, i.e. only two denominations of two pieces each.
Also included was a 16 MHz quartz resonator. 
I talked about capacitors and a quartz resonator in the last review, so I’ll just show where they should be installed.
Apparently, initially all capacitors were conceived of the same type, but 22 pF capacitors were replaced with small disk ones. The fact is that the place on the board is designed for a distance between the pins of 5mm, and small disk ones have only 2.5mm, so they will have to unbend the pins a little. You will have to unbend near the case (fortunately, the conclusions are soft), since due to the fact that the processor is above them, it is necessary to obtain a minimum height above the board. 
In the kit for the microcircuits they gave a couple of panels and several connectors.
At the next stage, we will need them, and in addition to them, we will take a long connector (mother) and a four-pin "dad" (not included in the photo). 
Sockets for installing microcircuits were given the most ordinary ones, although when compared with sockets from the times of the USSR, then chic.
In fact, as practice shows, such panels in real life last longer than the device itself.
There is a key on the panels, a small cutout on one of the short sides. Actually, the socket itself doesn’t care how you put it, it’s just that it’s more convenient to navigate along the cutout when installing microcircuits. 
When installing the panels, we install them in the same way as the designation is made on the printed circuit board. 
After installing the panels, the board begins to take on some form. 
The device is controlled using six buttons and two variable resistors.
In the original device, five buttons were used, the designer of the designer added the sixth, it performs the reset function. To be honest, I don’t quite understand yet its meaning in real use, since for all the time of the tests I never needed it. 
Above, I wrote that they gave two variable resistors in the kit, and there was also a tuning resistor in the kit. Let me tell you a little about these components.
Variable resistors are designed to quickly change the resistance, in addition to the nominal value, they also have a functional characteristic marking.
The functional characteristic is how the resistance of the resistor will change when the knob is turned.
There are three main characteristics:
A (in the imported version B) - linear, the change in resistance linearly depends on the angle of rotation. Such resistors, for example, are conveniently used in PSU voltage regulation nodes.
B (in the imported version C) - logarithmic, the resistance changes sharply at first, and closer to the middle more smoothly.
B (in the imported version A) - inverse-logarithmic, the resistance changes smoothly at first, closer to the middle more sharply. Such resistors are usually used in volume controls.
Additional type - W, produced only in imported version. S-curve adjustment characteristic, a hybrid of logarithmic and inverse-logarithmic. To be honest, I do not know where these are used.
Those who are interested can read more.
By the way, I came across imported variable resistors in which the letter of the control characteristic coincided with ours. For example, a modern imported variable resistor having a linear characteristic and the letter A in the designation. If in doubt, it is better to look for additional information on the site.
Included with the designer were two variable resistors, and only one had a marking :(
Also included was one tuning resistor. in essence, this is the same as a variable, only it is not designed for operational adjustment, but rather, it is adjusted and forgotten.
Such resistors usually have a slot for a screwdriver, not a handle, and only a linear characteristic of resistance change (at least I didn’t come across others). 
We solder the resistors and buttons and go to the BNC connectors.
If you plan to use the device in a case, then it might be worth buying buttons with a longer stem so as not to build up those that were given in the kit, it will be more convenient.
But I would put the variable resistors on the wires, since the distance between them is very small and it will be inconvenient to use in this form. 
BNC connectors, although simpler than in the oscilloscope review, I liked more.
The key is that they are easier to solder, which is important for a beginner.
But there was also a remark, the designers put the connectors on the board so close that it is impossible in principle to tighten two nuts, one will always be on top of the other.
In general, in real life, it is rare when both connectors are needed at once, but if the designers moved them apart by at least a couple of millimeters, it would be much better. 
The actual soldering of the main board is completed, now you can install the operational amplifier and microcontroller in their place. 
Before installation, I usually bend the leads a little so that they are closer to the center of the chip. This is done very simply, the microcircuit is taken with both hands by the short sides and pressed vertically with the side with the leads to a flat base, for example, to a table. It is not necessary to bend the conclusions very much, it is rather a matter of habit, but then it is much more convenient to install a microcircuit in the socket.
When installing, we look so that the leads do not accidentally bend inward, under the microcircuit, since when they are bent back, they can break off. 
We install microcircuits in accordance with the key on the socket, which in turn is installed in accordance with the markings on the board. 
Having finished with the board, go to the display.
In the kit they gave the pin part of the connector, which must be soldered.
after installing the connector, I first solder one extreme pin, it doesn’t matter if it’s soldered beautifully or not, the main thing is to ensure that the connector is tight and perpendicular to the plane of the board. If necessary, we warm up the place of soldering and trim the connector.
After aligning the connector, solder the remaining contacts. 
Everything, you can wash the board. This time I decided to do this before checking, although I usually advise you to flush after the first turn on, since sometimes you have to solder something else.
But as practice has shown, with designers everything is much simpler and after assembly it is rarely necessary to solder. 
You can wash it in different ways and means, someone uses alcohol, someone uses an alcohol-gasoline mixture, I wash the boards with acetone, at least until I can buy it.
Already when I washed it, I remembered the advice from the previous review about the brush, since I use cotton wool. Nothing, we'll have to reschedule the experiment for the next time. 
In my work, after washing the board, I got into the habit of covering it with a protective varnish, usually from below, since varnish on the connectors is unacceptable.
I use lacquer Plastic 70 in my work.
This varnish is very “light”, i.e. if necessary, it is washed off with acetone and soldered with a soldering iron. There is also a good varnish Urethane, but with it everything is noticeably more complicated, it is stronger and it is much more difficult to solder it with a soldering iron. Such a varnish is used for severe operating conditions and when there is confidence that we will no longer solder the board, at least for a long time. 
After varnishing, the board becomes more glossy and pleasant to the touch, there is a certain feeling of completeness of the process :)
Too bad the photo doesn't convey the big picture.
I was sometimes amused by the words of people like - this tape recorder / TV / receiver was repaired, traces of soldering are visible :)
With good and correct soldering, there are no traces of repair. Only a specialist will be able to understand whether the device was repaired or not. 
It's time to install the display. To do this, the kit gave four M3 screws and two mounting racks.
The display is attached only from the side opposite to the connector, since from the side of the connector it is held by the connector itself. 
We install the racks on the main board, then we install the display, and at the end we fix this whole structure with the help of the two remaining screws.
I liked the fact that even the holes matched with enviable accuracy, and without fitting, just inserted and screwed the screws :). 
All right, you can try.
I apply 5 volts to the corresponding pins of the connector and ...
And nothing happens, only the backlight turns on.
Do not be afraid and immediately look for a solution on the forums, everything is fine, as it should be.
We recall that there is a tuning resistor on the board and it is there for a reason :)
With this trimmer, you need to adjust the contrast of the display, and since it was initially in the middle position, it is quite natural that we did not see anything.
We take a screwdriver and rotate this resistor, achieving a normal image on the screen.
If you twist it a lot, then there will be a recontrast, we will see all the familiarity at once, and the active segments will be barely visible, in this case we just turn the resistor in the opposite direction until the inactive elements almost disappear.
Can be adjusted so that inactive elements are not visible at all, but I usually leave them barely visible. 
Then I would go to testing, but it wasn’t there.
When I received the board, the first thing I noticed was that in addition to 5 Volts, it needs +12 and -12, i.e. only three voltages. I directly remembered PK86, where it was necessary to +5, +12 and -5 Volts, and they had to be applied in a certain sequence.
If there were no problems with 5 Volts, and with +12 Volts also, then -12 Volts became a small problem. I had to make a small temporary power supply.
Well, in the process there was a classic, a search in the barrel of what it can be assembled from, tracing and making a board. 
Since I had a transformer with only one winding, and I didn’t want to fence the pulse generator, I decided to assemble the power supply unit according to the voltage doubling scheme.
To be honest, this is far from the best option, since such a circuit has a rather high level of ripples, and I had quite a back-to-back voltage margin so that the stabilizers could fully filter it.
Above is the scheme according to which it is more correct to do, below is the one according to which I did.
The difference between them is in the additional winding of the transformer and two diodes. 
I also delivered almost without a margin. But at the same time, it is sufficient at normal mains voltage.
I would recommend using a transformer of at least 2 VA, and preferably 3-4VA and having two 15 volt windings.
By the way, the consumption of the board is small, at 5 Volts together with the backlight, the current is only 35-38mA, at 12 Volts the current consumption is even less, but depends on the load. 
As a result, I got a small handkerchief, slightly larger than a matchbox, mostly in height. 
The layout of the board at first glance may seem a little strange, since it was possible to turn the transformer 180 degrees and get a more accurate layout, I did that at first.
But in this version, it turned out that the tracks with mains voltage were dangerously close to the main board of the device, and I decided to change the wiring a little. I won't say it's great, but at least it's a little safer.
You can remove the place for the fuse, since with the transformer used there is no particular need for it, then it will be even better. 
This is what the complete set looks like. to connect the PSU to the device board, I soldered a small hard connector 4x4 pins. 
The power supply board is connected to the main board using a connector, and now you can proceed to the description of the operation of the device and testing. Assembly at this stage is over.
Of course, it was possible to put all this in a case, but for me such a device is rather auxiliary, since I am already looking towards more complex DDS generators, but their cost is not always suitable for a beginner, so I decided to leave it as it is. 
Before starting testing, I will describe the controls and capabilities of the device.
The board has 5 control buttons and a reset button.
But about the reset button, I think everything is clear and so, and I will describe the rest in more detail.
It is worth noting a slight “bounce” when switching the right / left button, perhaps the software “anti-bounce” has too little time, it manifests itself mainly only in the output frequency selection mode in the HS mode and the frequency tuning step, in other modes there were no problems.
The up and down buttons switch the operating modes of the device.
1. Sinusoidal
2. Rectangular
3. Sawtooth
4. Reverse sawtooth 
1. Triangular
2. High frequency output (separate HS connector, other forms are for DDS output)
3. Noise-like (generated by random selection of combinations at the output of the DAC)
4. Emulation of a cardiogram signal (as an example of the fact that any waveforms can be generated) 
1-2. You can change the frequency at the DDS output in the range of 1-65535Hz in 1Hz steps
3-4. Separately, there is an item that allows you to select the tuning step, the default step is 100Hz.
You can change the frequency of operation and modes only in the mode when the generation is turned off., the change is made using the left / right buttons.
The generation is switched on with the START button. 
There are also two variable resistors on the board.
One of them regulates the amplitude of the signal, the second - the offset.
On the oscillograms, I tried to show what it looks like.
The top two are for changing the output signal level, the bottom two are for adjusting the offset. 
The test results will follow.
All signals (except noise-like and RF) were tested at four frequencies:
1. 1000Hz
2. 5000Hz
3. 10000Hz
4. 20000Hz.
At frequencies higher there was a large blockage, so it makes no sense to present these waveforms.
Let's start with a sinusoidal signal. 
sawtooth 
reverse sawtooth 
Triangular 
Rectangular with DDS output 
Cardiogram 
Rectangular with RF output
There is a choice of only four frequencies, I checked them
1. 1MHz
2. 2MHz
3.4MHz
4. 8MHz 
Noise-like in two oscilloscope sweep modes to make it more clear what it is. 
As testing has shown, the signals have a rather distorted shape starting from about 10KHz. At first, I sinned on the simplified DAC, and on the very simplicity of the implementation of the synthesis, but I wanted to check it more carefully.
To check, I connected the oscilloscope directly to the output of the DAC and set the maximum possible frequency of the synthesizer, 65535Hz.
Here the picture is better, especially considering that the generator was running at maximum frequency. I suspect that the simple amplification circuit is to blame, since the signal is noticeably “more beautiful” before the op-amp. 
Well, a group photo of a small “stand” of a beginner radio amateur :) 
Summary.
pros
High quality board manufacturing.
All components were in stock
There were no difficulties during assembly.
Great functionality
Minuses
BNC connectors are too close together
No HS output protection.
My opinion. Of course, we can say that the characteristics of the device are quite bad, but it should be taken into account that this is a DDS generator of the very initial level and it would not be entirely correct to expect anything more from it. I was pleased with the quality board, it was a pleasure to assemble, there was not a single place that had to be “finished”. In view of the fact that the device is assembled according to a fairly well-known scheme, there is hope for alternative firmware that can increase functionality. Taking into account all the pros and cons, I can well recommend this set as a starter kit for beginner radio amateurs.
Phew, that's all, if I messed up somewhere, write, I'll correct / supplement :)
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