I was looking for a circuit to fade an LED on and off using no microcontrollers, and found this nice circuit:
it seems like exactly what I was looking for, so I went ahead and used it with a few changes:
- I used a 2n2222 as the npn transistor instead of the BC547
- I used a 12V source instead of 9 volts because I'm using LEDs with from a 12V led strip (led + resistors all built into the strip).
- I used a 556 instead of a 555 because I had them on hand (and
I built the circuit as above (with the pinout changed accordingly for the 556), and it didn't work. I was a bit surprised, and double-checked all of the connections -- but they were all correct.
Would any of the changes altered how the circuit functions?
- I'm a bit concerned that changing the source to 12V might have effects, since that changes the threshold and trigger voltages -- could that be why the circuit isn't working?
- Should the leds and resistors be attached to the collector instead of the emitter of the 2n2222? I remember reading that LED driver circuits should be designed this way (something about V_be, IIRC).
- Any other ways that changing the circuit may have prevented it from functioning?