I picked up a cheap See ‘N Say toy at a thrift store a while back. I decided I would so something fun with it, which will hopefully make it into its own post after finishing it. At first I wondered about doing something with the audio clips that were stored on the toy. Of course, after opening it up there’s a big blob of black epoxy over the microcontroller. This makes reverse engineering it to dump the stored audio bits too much of a challenge.
Rather than give up, I decided I would put together a solution that’s good enough. I used a simple voltage divider with a potentiometer on one side to make adjustments to the audio output signal. I hooked the output of the speakers up to one end of the voltage divider and on the other end is a TRRS 3.5mm headphone jack breakout. The + from the speaker output is hooked up to the microphone ring on the jack and the – is hooked up to the ground.
For people wanting to follow along at home, there is no schematic for all situations. Each toy could have a different level of amplification or voltage output. Likewise each microphone input could have different expectations for voltage input level. I ended up using a 512K potentiometer and a 10K resistor. It’s very important to measure the voltage output to the speakers to determine how much resistance is needed to drop the voltage to a level suitable for a microphone input. You could end up damaging sensitive microphone electronics if you fed too high of a voltage into it.
I adjusted the potentiometer to adjust the signal to well below 1 volt peak to peak (1 volt is line level input) and measured it with my oscilloscope prior to plugging it into a computer. Once all hooked up, I started audio recordings on the computer and played the individual sounds from the toy by pressing each button. It’s a bit of a hack solution but was good enough to get quality audio out of the toy.