Hi,
I've built this circuit:
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On a breadboard and I'm struggling to get it functioning correctly. The LED just stays on..
How can you tell if the 555 timer chip is working?
- posted
13 years ago
Fading LED circuit with 555 timer.. LED stays on..
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- posted
13 years ago
led.html
Did you tie pin 4 to pin 8?
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13 years ago
g-led.html
Actually, I think pin 4 (TTL) will float high if unterminated. It's a good idea to connect it high if not used, but should float high if unterminated.
-Bill
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- posted
13 years ago
The fault may be the circuit design. If the BC547 has low gain then the circuit will never charge the cap to the required 2/3 supply voltage to make it change state. Try changing the 220 ohm resistor to 1k - 2.2k. Also in the original circuit substituting for the white LED with anything other than a blue will affect performance. With 2.2k it won't matter