Basic circuitry help? [not yet resolved] Answered
(I wasn't sure if this should be a comment on the Instructable or not, as it is a bit long, and I have some pictures..)
I am following a sound-reactive LE 1.D tutorial and having a bit of trouble. The circuit consists of a SPDT switch, resistor, LED, transistor, and a 3.5mm stereo jack. When I play music using this stereo jack, I get no response from the LED.
I'm trying to make something on a breadboard for the first time, so I'm thinking maybe I'm missing something because of that. Here's how the machine is supposed to work:
- Positive charge flows to SPDT switch, and if it's in the correct state, continues to the 150 ohm resistor
- Anode of LED is connected to the resistor, and the cathode is connected to the "emitter" lead of a TIP31 transistor ("base" is wired to the power bus)
- The "collector" lead of the transistor is attached to one of the outputs on the stereo jack
- The ground wire on the stereo jack returns to the common lead of the SPDT switch.
Perhaps I wired something wrong? I've included pictures if the description is not sufficient.
EDIT: I've modified the circuit a bit - maybe I can take pictures / draw a diagram tomorrow. Now, here's how it works:
- Positive charge flows from positive side of the power bus to the "base" lead of the transistor
- Collector lead of the transistor is connected to the left-channel lead of the stereo jack (also, the ground pin of the stereo jack is connected to the negative side of the power bus)
- Emitter lead of the transistor is connected to a 150-ohm resistor
- Resistor is connected in series with two LEDs
- The cathode lead of the second LED returns to the negative lead of the power bus
The LEDs do turn on now, but that's the problem - they are always at full brightness no matter the volume of the music. Even if no music is playing, the LEDs are fully lit. I've used a multimeter to check what's happening, and after pressing the negative lead of the multimeter to the cathode lead, and the positive lead to the anode lead, it shows a constant voltage of 1.986 V.
I don't understand how this isn't working - I've verified that the collector lead is correctly connected to the left-channel wire... maybe I should try the right channel? Or a different cable?
tl;dr: Rewired and the LEDs are always at full brightness. Transistor doesn't seem to be affecting the emitter output, for some reason..