LED or Lamp Pulser

Astonishing effect

4.5V supply

Circuit diagram

LED or Lamp Pulser-Circuit diagram


  • R1,R2 4K7 1/4W Resistors
  • R3 22K 1/4W Resistor
  • R4 2M2 1/4W Resistor (See Notes)
  • R5 10K 1/4W Resistor
  • R6 47R 1/4W Resistor (See Notes)
  • C1 1µF 63V Polyester Capacitor
  • D1 5mm. Red LED (See Notes)
  • IC1 LM358 Low Power Dual Op-amp
  • Q1 BC337 45V 800mA NPN Transistor

Circuit operation:

  • This circuit operates a LED in pulsing mode, i.e. the LED goes from off state, lights up gradually, then dims gradually, etc.
  • This operation mode is obtained by a triangular wave generator formed by two op-amps contained in a very cheap 8 pin DIL case IC. Q1 ensures current buffering, in order to obtain a better load drive.
  • R4 & C1 are the timing components: using the values shown in the parts list, the total period is about 4 seconds.


  • The most satisfying results are obtained adopting for R4 a value ranging from 220K to 4M7.
  • Adopting for R4 a value below 220K, the pulsing effect will be indistinguishable from a normal blinking effect.
  • The LED can be any type and color.
  • You can use a filament lamp instead, provided its features are comprised in the range 3.2 to 6V, 200mA max.
  • Using a lamp as a load, R6 must be omitted.
  • Voltage supply range can be 4 to 6V: 4.5V is the best compromise.
  • Don't supply the circuit with voltages exceeding 6V: it will work less good and Q1 could be damaged when a lamp was used as the load.
  • At 6V supply, increase R6 value to 100 Ohm.
author: RED Free Circuit Designs
circuit from http://www.redcircuits.com/