LM3915 Dot/Bar Display Driver

Vibration Meter

In this circuit, the LM3915 IC detects voltages that the piezo sensor creates when there is a vibration. Signal is measured via pin 5. The outputs that sink current drive 10 LEDs. The number of LEDs that are energized depends on the vibration intensity.

ULN2803A Darlington Transistor Arrays

The ULN2803 is useful for providing power to loads that cannot be handled directly by microcontrollers. Pins 1-8 are designed to receive low level signals. Pins 11-18 are the outputs. Put it simpy, It works exactly similar to transistor. Pin 1 drives pin 18, pin 2 drives pin 17, and so on. In this circuit, nine LEDS are interfaced with Arduino using ULN2803A IC. The digital I/O pins on the Arduino can only sink 40mA so that driving multiple LEDs is beyond its capabilities. The LEDs are powered by the 9V battery.

4060 14-Stage Ripple Carry Binary Counters

Row Of LEDs

Here, the CD4060 IC is configured to send signals to a row of LED lights. Each LED in a row is connected to the corresponding output pin of the IC. LED #1 is connected to pin 7 (Q3), LED #2 is connected to pin 5 (Q4), LED #3 is connected to pin 4 (Q5), and so on. Pin 12 (Reset) is connected to LOW for enabling the IC to function (oscillate). This demonstrates how the IC generates oscillations at its various outputs.

Keep The Output HIGH

This circuit uses the 4060 IC as a timer. Connect the pin 12 (RESET) to the positive pole of the battery and then connect to the negative terminal. The LED will illuminate after 5 seconds. The time delay period is determined by the 0.1 µF capacitor and the 1M resistor. The 1N4148 diode connects pin 7 (output) to pin 11 to block the oscillation. It keeps the output high until resetting.

4013 Dual D Flip-Flop

This circuit demonstrates the use of 4013 IC. Either the LED on pin 1 (Q) or the one on pin 2 (not-Q) lights up whenever the DATA input (pin 5) is connected either to a LOW voltage or to a HIGH voltage.The logic states of the outputs can only change when the CLOCK input (pin 3) is high at the clock edge. This follows the truth table of D flip-flop. For this purpose, the 555 timer is set-up to generate a low frequency clock signal (around 1HZ). A LED light is connected to pin 3 so that how the circuit responds to a change from LOW to HIGH can be seen easily. The set/reset inputs of the 4013 IC are connected to 0V.

4027 Dual JK Flip-Flop

Light Controlled Toggle Switch

4027 IC has four inputs (J, K, Set, Reset, and Clock) and two outputs (Q1 and not-Q). Here, a 4027 IC is designed in the toggle mode. The LED turns on or off and remain in that state whenever the resistance of the LDR changes. The 741 IC acts as a comparator. When light falls on LDR, Vin (pin 3) rises above or falls below Vref (pin 2) and the output changes polarity. The output is then sent to the clock input of the 4027 IC. According to the truth table, the output Q (pin 1) will toggle from one state to the other when both the J and K inputs are HIGH. Set (pin 7) and Reset (pin 4) are connected to the negative battery terminal. These pins are not dependent on the clock.

4047 Low Power Monostable/Astable Multivibrator

In this circuit, the IC 4047 operates on free-running mode. There are three outputs. A square-wave normal output is delivered through pin 10. Pin 11 is the inverse of pin 10. If pin 10 is high, pin 11 is low. The duty cycle will always be 50%. Output from pin 13 is twice as fast. The oscillation frequency is determined by the 39K resistor and the 1 µ F capacitor.

Arduino Development Board

This simple circuit uses an Arduino Uno clone to turn five LEDs on and off in sequence with intervals of 2 seconds - much easier than using a 4020 IC. The five LEDs are connected to the digital I/O pins (2,4,6,8, and10). The 330 ohm resistor that connects to the ground pin limits current. On the left is the code for the test program.









Knock Sensor Circuit

In the circuit above, the board is connected to a piezo sensor and a 7 segment. When the sensor detects a knock or vibration, it sends a signal to analog pin 0 of the microcontroller. Counts are displayed on the 7 segment display. When the count reaches 10, it will go back to zero. The variable hitscount in the code below stores the value. Sensitivity is set by the variable threshold.

LM358 Dual-Channel Op Amp

This shock alarm circuit is built around LM358 IC, a dual-channel operational amplifier. When pressure is applied to the piezo sensor, the stored charge is sent into the inverting terminal of the LM358. The LM358 is configured as an inverting Schmitt Trigger. Voltage thresholds are set using the 10K resistors. When the output is high, the threshold voltage is 3.33V. When the output is low, the threshold voltage is 1.66V. The output retains its value as long as the input is between the two levels. This implies a memory effect.

4017 Decade Counter

4017 IC has 11 output terminals. Pin 3 goes high when the count is zero. Pin 2 goes high when the count is 1 and so on. Unlike 4026 IC, just one of the individual outputs is HIGH at a time. This property make it useful for building a LED Sequencer. In this circuit, a number of LEDs turn on and off in sequence. The 555 astable circuit provides input clock pulses to the 4017 through pin 14. Pin 13 (disable) and pin 15 (reset) are connected to logic LOW voltage.

7404 Hex Inverter

In this circuit, a 7404 IC performs a logic invert function. A switch is connected to the pin 13 (input) of the IC and to the battery's negative side. By pushing the switch, pin 12 which is connected to pin 11 outputs a HIGH signal. Pin 10 outputs a LOW signal. LED 1 turns on and LED 2 turns off. When the switch is released, the circuit returns to its original state. In this case, LED 1 turns off and LED 2 turns on.

4020 14 Stage Binary Counter

Here, a 4020 IC is used to light up an LED light every 1 second. This IC does not have a built-in oscillator so that a 555 timer is used to generate clock pulses. In this circuit, the 555 IC generates a 1Hz signal. A 10K resistor, a 68K resistor and a 10µF capacitor are chosen for this purpose. The signal is then sent to the clock input (pin 10) of the 4020. 4020 IC has 11 outputs. In this simple project, only pin 9 is used. Reset pin (pin 11) is connected to the negative terminal of battery with a 100 nf capacitor. A high level at this pin will reset the counter.

When the LED lights are arranged like the picture below and each is connected to the corresponding pin on the 4020 IC, the LED 1 will turn on and off every 1 second. LED 2 will turn on and off every 8 seconds and so on...

7432 OR Gate

7432 is a voltage controlled device. The key parameters are Vih (HIGH Level Input Voltage), Vil (LOW Level Input Voltage), Voh (HIGH Level Output Voltage), and Vol (LOW Level Output Voltage). Vih is 2V (minimum value) and Vil is 0.8V (maximum value). An unconnected input (floating input) is considered HIGH (logical "1"). In this circuit a LED light that connects to pin 3 lights up when pin 1 and pin 3 TTL inputs are left floating. The typical supply voltage for 7432 is 5V. 7805 ic is used to turn down the voltage level from the 6V battery.

L293D Motor Driver

In this circuit, L293D IC is used for bidirectional control of two DC motors. A 9V battery amplifies the current to power the motor. Turning on one of the four switches makes one of the two motors rotates either clockwise or anti-clockwise. So not only drive the motors, the switches also control their rotation. The left motor rotates based on the input across the input pins (2 and 7). Pin 10 and pin 15 are for the right motor. Pin 1 and pin 9 (master control pin) allow you to enable the IC output pins. Both are set to logic high. This is a very simple circuit. There is no decoupling capacitor.

741 Operational Amplifier

This circuit could function as a simple alarm (light activated circuit). Without feedback, a 741 op-amp acts as a comparator. The input voltage (pin 2) is compared with a reference voltage (pin 3). You can see that there are two voltage dividers here (100K resistor + 4.7K resistor and 100K resistor and LDR). The sensitivity of the circuit is controlled by the 4.7K resistor that connects to pin 3. When light shines onto the LDR, its resistance falls. The voltage applied to pin 3 will be higher than the voltage at pin 2. The buzzer will sound. The buzzer should turn off when light is blocked.

The resistance of an LDR is high in the dark and at low light levels. In this dark activated circuit, the LED lights up when no light is present. When this occurs, the voltage at pin 3 is higher than the voltage at pin 2.

4026 Decade Counter

In this circuit, a 4026 IC used to drive a 7 segment led display (SM42056). The counting process is manually triggered by a tactile switch. What is great about 4026 16-pin CMOS is its output is suitable for direct connection to 7-segment LEDs. The simple manual trigger circuit uses a 6V power supply. A number of 330 ohm resistors are used as current limiting resistor. Pin 2 (Clock Inhibit), 8 (VSS), and 15 (Reset) are connected to the negative terminal of battery. Positive voltage is applied to pin 3 (Display Enable) and 16 (VDD). Pin 1 (Clock) is used to start the counting (1 push = 1 count). Pin 6, 7, 9, 10, 11, 12, and 13 are connected to the 7-segment.

555 Timer

In this circuit, a 555 timer IC is connected in astable mode to flash an LED on and off. The output from the 555 is a continuous pulse waveform. The output frequency is determined by the 1K resistor that connects pin 8 and 7), the 470 K resistor and the 1 microfarad capacitor. The timing capacitor charges through 1K and 470K resistors but only discharges through the 470K resistor. The rate of flashing can be slowed down easily by using a higher value resistor (i.e. 1M resistor).

HT12E HT12D Encoder Decoder Pair

HT12E and HT12D are normally used to transfer four bit data wirelessly. In this simple circuit, the medium is wire. The HT12E converts the parallel inputs (pins 10, 11,12, and 13) into serial output (pin 17). No need to connect a crystal oscillator to make it work. The data is then received by the HT12D that converts the serial input (pin 14) into parallel outputs (pins 10,11,12, and 13). Four LEDs are connected to the output pins. When a data pin in the HT12E encoder is connected to the positive terminal of the battery, the corresponding LED connected to the HT12D decoder glows. Both IC2 are capable of operating in a wide Voltage range from 2.4V to 12V.

7402 NOR Gate

7402 is a Quad 2-input NOR gate device. In this simple circuit, the 7402 NOR chip takes inputs at terminals 2 and 3. If both inputs are LOW, the output goes HIGH. The LED illuminates. If either pin 2 or 3 on the chip are connected to +5V, the LED will extinguish. Basically, a NOR gate is a combination of OR gate followed by an inverter. Pin 7 connects to ground and pin 1 connect to +5V. The 7805 IC converts 9V into 5V DC.

7805 Voltage Regulator

In this circuit, a 7805 IC is used to regulate 9V down to 5V. As you know, the voltage entering has to be at least 2V higher so that a 9V battery is used here. Two 0.1 microfarad capacitors are there to filter out any noise. Supposedly, a clean DC signal can be produced. The 5V DC voltage powers a LED light. The 200 ohm resistor limits the electric current to the LED (20mA).