Simple 2 Transistor LED Flasher Circuit
Here is a blast from past as they say with a transistor astable multivibrator. While today most people use a NE555 timer IC this version is simple to build. The LEDs altering on/off cycle whose flash rate is control by the two 22uF capacitors and the two 10K resistors.
Let's assume Q1 is turned off the collector rises to Vcc on the positive plate of the 22uF capacitor. During this time no current flow through the blue LED and it's turned off. At the same time Q2 is turned on and the red LED is turned on.
The two 22uF capacitors enter an altering charge-discharge cycles creating two square waves on the collectors that are 180 degrees out of phase. The flash rate is determined by the capacitor values and the two base charge resistors.
To get the Period:
P = t1 + t2 = 0.69R1C1 + 0.69R2C2 = (10,000 * .000022) + (10,000 * .000022) * 0.69= 0.3036 Sec.
Frequency = 1 / P = 1 / 0.3036 = 3.3 Hz.
The above formula assumes C1 = C2 and the capacitor value is converted to Farads. Another formula for frequency is:
f = 1 / P = 1 / 1.38RC = 1 / 1.38 * 10,000 * .000022 = 1 / 0.3036 seconds = 3.3 Hz.
In the video I used 5V and 12V and the change in voltage I observed no change in the rate of the LEDs on/off cycle. I'm sure it has some minor effect. The two transistors are NPN types and should be the same type. I used two TIP41A.
Note the capacitor and resistor values don't have to be the same. For example one capacitor can be 22uF and another 100uF where one LED stays on longer than the other.
- LM317 Constant Current Source for Lighting LEDs
- LM2575 Simple Switching Voltage Regulators
- Simple 2 Transistor LED Flasher Circuit
- Voltage Buck-Boost Transformer Connections Tutorial
- Arduino Buck Switching Voltage Regulator Demo
- Switching Regular Configuration Review
- Generating High Voltage with an Inductor
- Gen. Electronics
- My YouTube Channel
- Raspberry Pi & Linux
- Arduino Projects
- PIC18F2550 in C++
- PIC16F628A in Assembly
- PICAXE Projects
- Microchip PIC16F84A H-Bridge Motor Control
- Microchip PIC16F628A Basic H-Bridge Motor Control
- PICAXE Operates H-Bridge Motor Controller
- PICAXE Micorcontroller Controls Motor Speed - Direction
- PICAXE Projects
- Arduino Port Registers Revisited
- Digispark ATtiny85 with MCP23016 GPIO Expander
- Safely Build Program a H-Bridge
- Build H-Bridge Motor Control Without Fireworks
- MOSFET H-Bridge for Arduino 2
- Arduino Projects Revisited Revised
- Programming ADS1115 4-Channel I2C ADC with Arduino
- Arduino uses ADS1115 with TMP37 to Measure Temperature
- Connect Arduino to I2C Liquid Crystal Display
- Arduino Reads Temperature Sensor Displays Temperature on LCD Display
- Arduino with MCP4725 12-bit Digital-to-Analog Converter Demo
- Arduino with ADS1115 4-Channel 16-bit Analog-to-Digital Converter
- Arduino with MCP4725 12-Bit DAC
- Updated-Added Dec. 2014
- Constant Current Circuits with the LM334
- LM317 Constant Current Source Circuits
- Introduction Hall Effect Switches, Sensors, and Circuits
- Using Ratiometric Hall Effect Sensors
- Pulse Width Modulation Power Control for Microcontrollers
- Introduction to PIC12F683 Programming
- Basic Transistor Driver Circuits for Micro-Controllers
- Opto-Isolated Transistor Drivers for Micro-Controllers