Hoping for some advice on circuit I am working on.
I have purchased some large gameshow type buttons, each of which lights up and plays a unique sound when pressed. My aim is to hack these in order to control them from an Arduino (via USB) and create various games.
Each button has it's own independent power supply (2xAAA battery) which I plan on leaving as is to power the internal circuit, speaker, and LED. On the small circuit board, there are 4 pads, each of which plays a different sound simply by applying a 3V pulse to the pad.
I have got to the point where I can trigger the sound using the circuit below. SOUNDTRIG is connected directly to the pad on the button. By briefly switching NANO-D3 high and low, I can successfully trigger the sound. However, the sound also triggers whenever I apply power to the Nano. This would be annoying when all 4 buttons are connected.
Is there anything I can do to prevent this happening or is there a much simpler way of achieving this? Also when I touch a multimeter probe to the base of the transistor, the sound also triggers.
Any help or suggestions would be most appreciated.
base of R2 was a typo on my part. Corrected that to base of transistor.
The external button circuit is very minimalist so I can't tell whether it has a micro or a specialised chip since it's covered by a big blob of epoxy. If I just take the button in isolation, the voltage on the pad measures 0V when unpressed. When pressed, the voltage is 3V which is all that seems to be required to trigger the sound and LED.
Would creating a simple voltage divider off D3 and switching the pin high and low be a better solution for what I'm trying to achieve?
The turn on pulse happens because the NPN transistor is biased "off" and the resistor pulls up. If you reverse things so the resistor pulls down, use a PNP transistor with the emitter connected to 3.3V, the initial state would be 0V.
To be really universal and safe, an optoisolator would be the best interface.
