I'm building a BMX start gate controller. It requires a voice sample to be played ("Riders ready, watch the gate!") before playing a series of tones at very specific frequencies and intervals. After the tones are complete, a relay is triggered which drops the start gate.

I'm intending to use one of the header pins with the tone() function to output the tones, and an Adafruit AudioFX board to play the voice sample.

How do I connect both of these to an Adafruit mono amplifier (https://www.adafruit.com/product/2130) ?

Note that only one or the other will be playing at one time.

Can I use a "passive mixer" (which I think is putting a 10kΩ resistor on each input source for the amplifier?)

1 Answer 1


Yes, a passive mixer would do fine. I would recommend capacitors to remove any DC component too, before you do the mixing. 22uF should do fine.

I will draw a circuit in the morning.

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