Digital Tester on a K155LA8 Microcircuit

Frequency meter – digital scale (up to 40 MHz)

To tune up transmitting and receiving devices, a frequency meter is indispensable. With a frequency meter and a simple signal generator you can measure capacitance, inductance, temperature and other quantities. Described in the book by J. S. S. Lapovok “I build a radio station” digital scale TsSh-1 can work as a frequency meter.

The advantage of the TsSh-1 is a very good decoupling from the input signal source, which is necessary to avoid interference from the device. The maximum measured frequency is about 40 MHz, accuracy – 1 Hz. The principle of TSH-1 is to accurately measure the frequency of the input signal by counting the number of periods of the input voltage during the time interval generated from a highly stable crystal oscillator.

Frequency stabilized crystal oscillator ZQ1 assembled on a chip DD16 K155LA3. This oscillator has a frequency refinement element – selective capacitance C3*. The rectangular pulses with a frequency of 100 kHz from the output of DD16 are fed to the input of a chain of six decimal counters DD17. DD22 K155IE1. By means of switch SA2 the counting accuracy of 1kHz or 1Hz is set. From the output DD19 or DD22 short negative pulses with repetition rate of 100 Hz or 0,1 Hz are fed to the shaper of square pulses of counting interval with duration of 0,01 s in measuring mode with 1 kHz accuracy or 10 s in measuring mode with 1 Hz accuracy. This shaper is built on half of the K155TM2 chip DD25.2 and the DD3.2, DD3.3 elements of the K155LA3 chip.

Pulses of the counting interval control circuitry DD2, DD11. DD15, the shift register built on the DD23, DD24, and a half chip DD25.1, and to control the operation of the chip DD10. The input voltage is fed to the KP302BM transistor VT1 arranged in a source repeater circuit, which provides a high input resistance of tSP-1 and its good isolation from the signal source output. Transistor VT2 KT603B controls the operation of a square-wave pulse shaper with the input signal frequency assembled on the DD1.1 and DD1.2 elements of K1533LA3 chip. These elements are covered by a positive feedback circuit through resistor R4 and create at input DD2 a very clear rectangular pulses, due to which the decimal counter DD2 K155IE2, formally operating at frequencies below 20 MHz, perfectly copes with the counting of pulses coming with a frequency up to 40 MHz.

The counting of the number of pulses of the input signal for a time of 0.01 s or 10 s is done by a chain of decimal counters DD2, DD11. DD15. The first of them serves to reduce the input signal pulse frequency at input DD11 by a factor of 10 and is not used for frequency indication, which improves the stability of the tsSh-1 indicator readings. The thing is that the input signal frequency is not synchronized with the generator frequency at ZQ1, so if the input signal frequency is constant, the results of pulse counting by DD2 during a constant time interval can differ by one, then the lowest bit of binary code of pulse counting at DD2 outputs will be unstable. Accordingly the reading of the digital indicator will be unstable if it is connected to DD2. The random change of the low-order bit on the output of the next counter – DD11 – is possible only when the highorder bit on the output of DD2 is changed. Thus the instability of the low-order bit of the binary number on the output of DD2 does not affect the stability of the digital indicator connected to the outputs of DD11.

The +U to -U voltage converter on the CD4049 chip, schematic.

The microcircuits DD11. DD15 K155IE6 – reversible decimal counters with preset count rate. The reversibility of the chips is used as a digital scale when the tuning frequency of the receiver decreases with the increase of the heterodyne frequency. The +/- pin, DD1.3, DD1.4, DD3.1 elements of the K1533LA3, K155LA3 chips are used to switch the DSH-1 operation for adding or subtracting the heterodyne frequency. After the positive pulse on input 12 of DD1.3 ends, a positive pulse appears on its output 11, which goes to the “+” input of DD11. Since the counting time in the DD11. DD15, defined by the duration of a positive pulse on their outputs 11, is equal to 0.01 s (10 s) and the input signal frequency to input DD11 is divided by 10, then the number of counting pulses in DD11 is equal to the number of kilohertz (Hertz) of the input signal frequency, In DD12 – tens of kilohertz (Hertz) of the input signal, in DD13 – hundreds of kilohertz (Hertz), in DD14 – units of megahertz (kilohertz) and in DD15 – tens of megahertz (kilohertz) of the input signal.

In the K155ИЕ6 chips, applying a positive voltage to pin 15 introduces an initial count rate value of 1, to pin 1 – 2, to pin 10 – 4 and to pin 9 – 8. Disconnecting these leads from the case is equivalent to applying a positive voltage to them. When working as a digital scale, the indicator readings should not be equal to the heterodyne frequency, but to the tuning frequency of the receiver, which can be above or below the intermediate frequency. For example, in the receiver with IF equal to 465 kHz in the medium-wave band, where the LO frequency exceeds the reception frequency by the IF value, the DD11, DD12 have pins 1, 10; DD13, DD15 have pins 1, 9; DD14 has pins 10,9 connected to the case, the remaining preset pins of DD11. DD15 is connected to +5V via a 1K resistor, and the counting inputs are switched to add. As a result the kilohertz frequency counting starts from the value 99535. In this case after counting 465 pulses the counting result in DD11. DD15 will become 00000, i.e. the receiver IF frequency will be subtracted from the heterodyne frequency. When the TsSh-1 works as a frequency meter all preset counting frequency pins are connected to the case.

Powerful, adjustable lm317 based power supply

The device uses five LED sign indicators ALS324B with a common anode. The same segments are connected together and connected to the outputs of the decoder DD10. To indicate in each digit of any number the indicators work in dynamic mode – each indicator is connected to its counter digit in turn with simultaneous switching it on through transistor switches VT3. VT7. The dynamic mode of indicators is organized as follows: on the outputs of DD23.1. DD25.1 shift register cells five consecutive pulses of counting interval appear. Each of these pulses is fed to inputs 2, 5, 9, 12 of DD4. DD8 OF THE K155LA8. The inputs of these chips are connected to the outputs of the DD11. DD15, on which the binary codes of the kilohertz (hertz) frequency of the input signal are formed. The outputs of DD4. DD9 are combined in the “mounting or” (it allows outputs “open collector”) and connected to the inverter, built on a chip DD9 K155LA8. From the outputs of DD9 binary number of kilohertz (Hz) frequency input signal goes to the inputs of the decoder DD10 KR514ID2, which turns this number into seven voltages, which are fed to the appropriate segments of indicators. From the five outputs of the counting register the pulses are fed to the transistor switches VT3. VT7, which turn on the corresponding indicator, according to the counter connected to the decoder. The counter interval pulse is fed to pin 3 of DD10, so that the voltages on the indicator segments are formed after the end of counting in DD11. DD15.

Instead of K155 series chips you can use chips of other series, for example, K133, K555, K1533. For more details on the function of series K155 chips, see the excellent book by S. A. Biryukov “Digital Devices on Integrated Circuits. The DD17. You can use K155IE2 as DD22 by connecting their pins like DD2 (in this case pins 2,3 are connected to the case). K155LA3 can be used as DD1, but the maximum measured frequency will decrease to 25 MHz. Microprocessor power leads: +5V is fed to pin 14 of К1533ЛА3, К155ЛА3, К155ЛА8, К155ИЕ1, К155ТМ2 and КР514ID2, pin 5 of К155ИЕ2 and pin 16 of К155ИЕ6. The common wire (-5V, connected to the case ) is fed to pin 7 of K1533LA3, K155LA3, K155LA8, K155IE1 and K155TM2, pin 10 of K155IE2, pin 6 of K514ID2 and pin 8 of K155IE6.

Simple Switching Power Supply on IR2153

Instead of the 100kHz quartz ZQ1, you can use a quartz for another frequency by changing the DD17 divider chain accordingly. DD22. Some quartz resonators, like WG-01 are excited at higher harmonics, so you have to connect C5* for a short time with a capacity of a few tens of nanofarads.

KP302BM can be replaced with KP302, KP303, KP307 series transistors; KT603B can be replaced with any of the KT603, KT608 series; KT208,KT209, KT502 with any letter can be used instead of KT3107B. R2*, R3* must be chosen to achieve maximum sensitivity of the frequency meter. To equalize the brightness of the luminosity of the sign indicators in the collector circuits of VT3. VT7 can be fitted with resistors.

The frequency meter is assembled on a single sided foil textolite board, all connections are made under the board with the shortest insulated conductors. The device is powered from any stabilized power supply with voltage of 5 V, current consumption – 0,7 A.

Literature: 1. Lapovok Ya. 1. I am building a radio station. – Moscow: Patriot, 1992. 2. Biryukov S. A. Digital Devices on Integrated Circuits. – М.:1991.

К. С. Selin Ukraine, Zhitomir Dukalis1 (at) Source:

A Simple Logic Trial

Hello, dear readers of For the adjustment of the clock generator appeared a necessity in a logic tester. On the Internet I found nothing useful, because the circuit, which I took from the sites did not work, and if they worked, not as it was necessary. Therefore it was decided to develop my own circuit for a logic probe, the appearance of which you can see in the photo below.

The logic probe appearance

Probe of logic probe

The logic probe display

The sampler circuit was made with the Soviet chips K176IE8 (CD4017) and K155LA3 (SN7400), which I had in the presence.

K155LA3 and K176IE8 chips

The K155LA3 chip consists of four 2I-NE elements fed from a common DC source, with each element working as an independent chip. All four elements have three pins, where each element is identified by pin numbers. So, for example, input pins 1, 2 and output pin 3 refer to the first element, and input pins 4, 5 and output pin 6 refer to the second element, etc.

Quick heating soldering iron with his own hands

Pins 7 and 14 of the microcircuit, serving for power supply, in the schemes are not marked, because its elements can be located in different parts of the circuit of the device. Each element on the circuit diagrams is indicated with an alphanumeric index: DD1, DD2, DD3, DD4.

Pin assignment of K155LA3 chip

Microcircuit K176ИЕ8 is a decimal counter with a decoder and has three inputs R , CN , SR and nine outputs Q0 … Q9 .

Input R (pin 15) is used to set the counter in its initial state, at input CN (pin 14) apply counting pulses of negative polarity, at input SR (pin 13) apply counting pulses of positive polarity, outputs Q0 … Q9 (pins 1 – 7 and 9 – 11) are counter outputs. In the initial state the outputs Q1…Q9 are log. 0 and Q0 is log. 1; Plus supply is applied to pin 16 and minus to pin 8.

Pin assignment of K176IE8 chip

The counter of the microcircuit is set to 0 when the logic 1 (Log.1) is fed to the input R, this means that the output Q0 shows log.1 and the outputs Q1 – Q9 – logical 0 (Log.0). For example. It is required that the counter counts only up to the third digit Q2 (pin 4). To do this connect pin 4 with pin 15. When counting up to the third digit is reached the counter will automatically switch to counting from the beginning.

The counter states (outputs) are switched by the negative polarity pulses at the CN input. At the same time there must be a logical 0 on the SR input. You can also supply pulses of positive polarity to the input of SR , then switching will take place on their falls. At the same time at the input of CN should be a logical 1.

The schematic of the logic tester is shown in the figure below.

Schematic diagram of a logic probe

The operation of the circuit is very simple. When positive pulses come to the CP input of the DD2 chip, the counter outputs are switched, indicated by LEDs. According to the blinking of LEDs the process of operation of the tested oscillator or any other digital device is observed.

Making a simple LED light-music system with your own hands. Schematic.

If the input voltage is less than 2/3 of the supply voltage, or there is no supply voltage at all, the counter is unstable. In this case the switching of LEDs is chaotic and such a state can be considered as a logic 0. When logical 1 is applied to the input the counter is switched clearly and the probe gives a sound signal. Sound generator is assembled on the elements DD1.1 and DD1.2 of the chip K155LA3 and the transistor VT1 KT361B.

I have used four LEDs in my meter and I think that this is enough to visualize the process. In this case there is even some convenience in the measurement, which gives a little pause when switching the counter to the initial state. If someone wants to use more LEDs, the pin 15 of the DD2 chip is connected to the next output in order. In my version pin 15 is connected to counter pin 1.

The sounder can also be used without the buzzer. For this purpose we exclude the sound generator assembled on the DD1 elements, VT1 KT361B, R1, R2, C1, sounder ZP-22 from the circuit. In this case the measured signal level is fed only to the SR input of the meter.

The probe is powered from the device under test, which is very convenient.

The circuit is assembled on a single-sided board and has a small size, which allows you to make the device compact. Any low voltage LEDs can be used. The housing is made from an eyeglass case.

Parts side of logic probe board

View of component side of logic probe board

View of trace side of logic probe board

The probe is a piece of copper wire with a cross section of 3 mm and a length of 5 cm. In the working version of the device the input part is done without diode and transistor, which are not shown in the schematic diagram. As practice showed, this change significantly increased the sensitivity of the logic probe.

Also take a look at the video which shows how the logic probe works.

You can download the board in lay format here.

See you on our site! Anatoly Tikhomirov (picdiod), Riga Good luck!

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