I am using a sound board from Adafruit (this one) to play a small sound file.
What I would like to do is to close a transistor while the sound is playing, which will then close the circuit on a few LEDs. This will cause the LEDs to light while the sound is playing, and then turn off.
After finally finding the pin-out explanation there, I see that it has an
ACT[ivity] pin which signals when audio is playing. While the board is on, the pin normally sits at roughly 3.35V, and then when the sound plays, the voltage drops by around 2 - 2.5 V. I see no change in amperage across the pin while the sound is playing.
As I understand it though, transistors switch when a positive voltage is applied to the base/gate. So I'm not sure what to do here. Is there a way to switch the transistor in such a way that when the
ACT pin is sitting at 3.35V the transistor is open, and then closes when the applied voltage drops?
I tried to google on this, but all the articles and pages coming up have to do with the voltage drop across the transistor, nothing about switching the transistor based upon a voltage drop.
Below is the segment of my circuit I am trying to figure out at this point...
Originally, I was planning on using the second speaker output on the board to switch my transistor, but that seems to have a constant voltage and amperage whether it's playing or not. Then I found the board's pin-out and the
ACT pin, so I'm trying to make this work off of that now.