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This is an LED pulse effect circuit. The effect result of this circuit is that the LED goes from off state, lights up gradually, then dims gradually.
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 and C1 are the timing components: using the values shown in the parts list, the total period is about 4 seconds.
R1,R2 _________4K7 ohm R3 _________22K ohm R4 _________2M2 ohm (See Notes) R5 _________10K ohm R6 _________47R ohm (See Notes) C1 _________1µF/ 63V Polyester Capacitor D1 _________5mm. LED (See Notes) IC1 _________LM358 Low Power Dual Op-amp Q1 _________BC337 NPN Transistor
Notes:
- 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 bulb instead of the LED, provided it is rated in the range 3.2 to 6V, 200mA max.
- Using a bulb as a load, R6 must be omitted.
- Power supply range can be 4 to 6V: 4.5V is the best compromise.
- Do not supply the circuit with voltages exceeding 6V: it will work less good and Q1 could be damaged when a bulb will be used as the load.
- At 6V supply, increase R6 value to 100 Ohm.
Original page of this LED Pulse Effect circuit:
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