15 Small digital circuit ideas for beginner

I like to collect the circuit diagrams. Because when I want to create a great project. Sometimes, even we check it well. But it does not work.

The good solution is using small these circuits.

Here are 15 digital circuits.

Some circuits maybe not passed tested. Please be careful to build. My meaning is it may not work as want. You may modify it first to real uses.

Buffer circuits for digital CMOS

If you want the circuit Output buffer for the circuit digital. I suggest the IC-4050 (Hex buffers with high-to-low level shifter inputs) because very be IC that be usable easily. use link up digital circuit TTL and CMOS well.

The family of CMOS digital ICs has many strengths. It can be used to power a 3-16V, Easy and cheap. It has the same frequency is not high. A slow response that IC – TTL applications are easy to use and cheap. Slow response to IC – TTL applications. The problem that I found as the current is low. Do not apply to other circuits or the load current is greater than 50mA. However, we have several ways to increase the buffer circuit such as the transistor and a buffer circuit. This circuit continues on this issue, we use the IC 4050 is characterized by several parallel butter gate. However, we have several ways to increase the buffer circuit. Maybe uses a transistor and a buffer IC circuit.

Output Buffer circuit using CD4050

In this circuit, the answer to this problem, we use the IC 4050 is characterized by several parallel butter gate. Normally single gate circuit can supply up to about 15mA. When we put the gate parallel together will help Increases the current very well. The circuit is in highly stable up.

Buffer circuits for digital CMOS

Linear x10 Amplifier by 4011 Gate

This is very basic amplifier circuit,so I use IC digital Cmos 4011 quad NAND gate.
It is to give equal to 10x linear amplifier.
The resistor R1 = 1M ohm , R2 = 10M ohm.
This circuit can not output speaker because it is very low power amplifier.

1 Hz Timebase circuit using IC-4017

I used input frequency 10Hz to output 1Hz.This is a 10 divider circuit.
When we need a standard digital clock 1 Hz. but we have the input signal is square wave form 10 Hz so need to reduct it lower with digital frequency divider circuit 10 times.
I suggest that IC 4017 (Decade Counter / Divider with 10 Decoded) from the familiar to make a 10 LEDs running light circuits, but this circuit we used a frequency dividing circuit 10 times, too.
It’s interesting because it uses a single IC run it. The circuit is very simple. Would not be very descriptive. Enjoy it.

1 Hz Timebase circuit using IC-4017

Circuit diagram of the 1 Hz Timebase by IC-4017

Two divide counter circuit using IC-4027

When you want to decrease the frequency in 2 digital times circuits or Divide Frequency by 2 counter. I advises use IC 4017, because seek easy cheapness can be usable good various.

Two divide counter circuit using IC-4027

A diode protect CMOS circuit

The CMOS digital circuit used to produce an oscillator, with pulse low-frequency form. We use R and C are a lot of period of time. it must have a diode to prevent current flow feedback.

A diode protect CMOS circuit

In the oscillator circuit, we use the CD40106 and 74HCT132.The D1 and D2 connected to the input terminal of the twin IC respectively. These diodes should be outside the IC, because if the diode within the IC. When too much current flow will cause the loss diode and IC too.

Level Voltage of Logic Changer using JFET

This is a logic signal changer circuit, the normal voltage of about 5V. But sometimes we want to 12V or 15V, we can use a JFET. It works by mode COMMON GATE.

The simple principle is that when a logic “0” or 0V. The JFET N-channel type which will stop the conduction, The voltage between D and G was 0V too. And if logic “1” with the voltage 5V, N-channel conduction.

The voltage between pins D and G is equal to VS, which may be equal to any 12 Volt or 15 volts.

The Level Voltage of Logic Changer by a JFET

The R1 will determine the speed and power loss of the circuit, the resistance R1 is in the range of 100K to 1M, so the current flowing through it is in the 150uA to 15uA.We can also determine the frequency of the pulse matches with. The limit of approximately 1 MHz.

A key advantage of this circuit is, can be applied to the device driver voltage is higher than 5 volt.

Automatic duty factor controlled circuit

This is an Automatic duty control circuit. We can use the Schmitt trigger to generate the simple square wave. The duty factor of the output waveform will be determined by the input waveform. But the threshold level is the importance.

In Figure 1 will have the output while input waveform as Figure 2 cannot have output.

Automatic duty factor controlled circuit
Figure1 Automatic duty factor controlled circuit

the waveform of this circuit
Figure 2 the waveform of this circuit

How Automatic duty control works

The small input signal is connected to the circuit through the capacitors C1. The level of output is the average by R2 / C2 and feedback to input.
The adjustment of the DC voltage at the input to control the peak voltage of the input signal.

When the input signal is fed into a large excess of the threshold level of Schmitt trigger both positive and negative side. It will be a square wave at the output. The sensitivity of the tuned circuit at P1.

The disadvantage of this circuit is that. If no the input signal. The circuit is working as a frequency generator. To prevent this problem, We must have a frequency of at least 10 times. (The circuit is 100 Hz,)

Using this circuit may be used as a trigger to automatically oscillator’s frequency spectrum.

Another disadvantage of the circuit. If the input signal is a very small duty factor at the top of the sign. The pulse output quality is not good.

Parts you will need
IC1: CD40106, CMOS Hex Schmitt Triggers
R1: 1M, 0.25W Resistors tolerance: 5%
R2: 100K, 0.25W Resistors tolerance: 5%
C1: 100nF or 0.1uF 50V, Polyester Capacitor
P1: 1M Pot

Pulse delayer circuit using CD4528

The Pulse delayer circuit this use IC 4528 help delay pulse or oscillator the all. For a signal is a pulse that postpones long ago go up. By fix give R1 control while delay, R2 control the wideness of pulse to delay. The detail is other see in circuit picture.

Pulse delayer circuit using CD4528

7 Stage Binary Counter Display with LED using CD4024

This circuit basically the base of the usability IC number CD4042 (7 Stage binary counter). By the circuit will regard the binary digit arrive at 128 BIT. Then show with LED 7 the make easy build the education.

7 Stage Binary Counter Display with LED using CD4024-IC

When feed power supply give with the circuit IC1 as a result will change way position output every time. When receive pulse signal from pressure switch S1. By pin 1 (CK) will receive pulse signal pin edge goes up to are logic “1” and when liberate switch receive signal pin edge down is logic “0” thus when press switch S1 time that 2 LED2 stick bright. But LED1 switch off which be the show output the two base is 001 and when press switch S1 time that 3 LED1 and LED2 stick bright. But LED3 switch off display be output the base is two be 011. when press switch time build go to as a result will display be the binary digit goes to continually until arrive in time that 129 which LED1-LED7 will stick bright and the integrated circuit will do something reset begin count at new zero output every a leg has will logic “0” cause LED1-LED7 switch off be finished every.

4511 Binary to Decimal decoder

4511 Binary to Decimal decoder
This isn’t a very useful or interesting circuit but it demonstrates the prinicple of a Binary to Decimal decoder IC such as theIC 4511.

Counter Display with LED 7 Segment Using CMOS

This is the simple digital counter circuit, the IC application number 4029 from binary data, and then sent to the IC number 4513, a driver IC 7 Segment, to show off a digital number from 0 to 9.

When entering into a pulse signal input pin 15 of IC1, it will signal to the output signal is Binary.Then send the output from the pin Q0, Q1, Q2, Q3, and the pin. 6, 11, 14 and 2 of IC1.Go to the input of IC2 No. 4513. Which is IC displayed by the decoder signal to the Binary LED display with a 7 or the 7 Segment, will be displayed from a digital number from 0-9.

Counter Display with LED 7 Segment Using CMOS IC

The Schematic Diagram of LED 7 Segment Counter circuit using CMOS

0-99 Two Digit Counter By IC 74LS48 , 74LS90

This is circuit 0-99 Two Digital Counter.
use IC TTL Digital IC 74LS48 x 2 to LED 7 segment Display,
and 74LS90 x 2 for Decade and Binary Counters.
Input Clock pin 14 from IC 74LS90.
Here is circuit use power supply 5V.

0-99 Two Digit Counter By IC 74LS48 , 74LS90

2-Digit Seven-Segment Pulse Counter Module

LED display with NAND gate digital control

This circuit operates in the digital circuit.It has 2 inputs are inputs inputs A and B inputs to receive input, By used nand gate ICs,To control the on-off of the lamp.

Operation of the circuit. When the input to the A is listed as “0” or “1”.And B is listed as “0” will cause the output of IC1 / 3 to “0”.The Q1 does not work will not light LED1.But if the A is listed as “0” and B is listed as “1” will cause the output of IC1 / 3 to “1” As a result, Q1 LED1 light work.

LED display with nand gate digital control

But if the A is listed as “1” and B is listed as “1” will enable LED1 blinking frequency of approximately 3.5 Hz.The principle is working. The first two legs of the conditions IC1 / 1 “0” to the output Into “1”.And IC1 / 2 off the output is “0” IC1 / 3 to return to the status output from a “1” LED1 is light.And caused a charge of C1.This will take and when will fully charge C1 pin 2 of IC1 / 1 is “1” makes the output from “0”.And IC1 / 2 off the output is “1” and IC1 / 3 to return to the status output from a “0” LED1 is extinguished. And caused the discharge of C1 through the voltage of R2 through the voltage of C1 gradually decreased.The voltage at pin 2 of IC1 / 1 to 0 volts of this work will continue, causing LED1 flashes.

Rising-edge trigger R-S Flip Flop circuit

The normal R-S flip flop circuit include of two nade gate are connected together and when need to set or reset then feed the logic signal is “1” instead trigger and use inverter work instead.

Rising-edge trigger R-S Flip Flop circuit

In Figure 1 suppose begin state of both input is “0” and output Q is “1”, input of N1 will be pulled to “1” by the 180 K resistors. Thus output Q so is “0”, that input of N2 is also “0”. Then if feed logic “1” to input s output -Q will be “0” pull input of N1 is also “0” and output Q will be “1”.

Thus input of N2 will be pulled as “1” Although input S is “0” another matter. And When feed logic “1” into the input R will reset the flip flop and Process change would be opposite to the above.

The R-S flip flop circuit should drive easily the load that has resistance of 180K at logic “1”. The CMOS circuit can drive the load on this already.

Digital logarithmic sweep signal generator circuit

This is a Digital logarithmic sweep signal generator circuit by using the average digital. It uses together with the frequency generator by voltage controller.

How Digital logarithmic generator works

In the circuit, the 14-bit binary counter circuit, that input is synced with the output of oscillator generator circuit. Then, the 8 output of IC-4020 is connected to the resistor networks, that will change the digital code to the DC voltage level.

Digital logarithmic sweep signal generator circuit
Digital logarithmic sweep signal generator circuit

Thus, the DC voltage level from zero to about 0.2Vb. So it is divided into 256 steps. But lower output will not connects to any things. It cause the DC voltage level Uo increased step by step. After that, the clock through 128 cycle. This output can continue to sweep input of the oscillator is controlled by voltage.

A frequency generator from the circuit (And frequency synchronization output) increases every time the control voltage increases. This makes the voltage and frequency increased almost as exponential required.

When applying Uo from the oscillator controlled by voltage into Vin of this circuit. The resistor R9 the t input of IC2 must change to direct connect. Thus no logarithmic voltage at Uo, But it is only the output of IC2.

The circuit connecting
The circuit will connect two sections in together with adjusting as follows. To connects the reset wire to connect temporarily reset to IC4020, across reset pin to a positive voltage. Then, adjust the frequency at pin 11 of XR2206 take output is 80Hz.

Next, Disconnect the reset wires from the positive to ground instead. Then, adjust start bottom to “connected” the sweep frequency (the clock frequency of IC1) will start at lowest frequency (80 Hz) and long times about 1 Second. After that, the IC1 will increase the frequency in step by step until you reach 20 KHz.

The speed of sweeping can increase is 2 times, by connected to resistors R1 to R8. In the sweeping circuit, Q6 to Q13 replace output Q7 to Q14 and If move to Q5 – Q12 instead will can get speed up to 2 times. The speed of the basic clock can multiply with 8 by connecting output Q4 to Q11.


I always try to make Electronics Learning Easy.

Apichet Garaipoom

I love the electronic circuits. I will collect a lot of circuit electronics to teach my son and are useful for everyone.
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