This circuit operates a LED in pulsing mode, i.e. the LED goes from off state, lights up gradually, then dims gradually, etc.this gives an astonishing effect with 4.5V supply.
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 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.
Voltage 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.
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