Vtech Apple Part 2 – Exploration and Pitch Adjustment

circuit bendingIn Vtech Apple Part 1 I got started bending my new Apple toy by adding a kill switch and audio output. Now with those modifications in place we can really start to have fun with the circuit, today I’ll be taking you through some cursory circuit exploration and I’ll add my first bend to the circuit, a basic pitch/clock control. Before we get to far in though I’d like to go over the 2 main techniques I use to explore a circuit for possible bends :

Lick and Stick

This is something of a “wide brush” approach as it is not exact but can help to identify areas where bends will be possible. Typically the first thing I do when I open up a circuit is trigger a noise, lick one of my fingers and begin lightly pressing on different solder connections across the board. When doing this your finger will act as a connection between the points it touches (with a small amount of resistance added) and you should be able to start eliciting different reactions from the circuit. As you go mark down on a photograph or a piece of paper where you were able to get different effects from.

Probes

Once you have found some possible bend points it is time to refine and identify exactly which points you’ll be attaching wires to. To do this it is best to use a set of connected probes. If you do not have probes on hand you can make an impromptu set very easily by connecting two jewelers screw drivers with a set of alligator clips. Touch the probes to the different solder points you identified with the “lick and stick” method, To explore further options you can try placing different resistors or a potentiometer between the probes with alligator clips. Again mark down any bend points you identify on a photograph of the circuit or a piece of scrap paper.

Pitch Bend

Vtech Apple - Pitch Bend CircuitTypically the first bend I complete on a toy once I’ve explored the circuit is a basic pitch bend. On most toys the clock speed for the processor is set by a resistor placed somewhere on the board, through my exploration of the circuit I was able to identify that this was done using the resistor marked R1 on the bottom of the circuit board (highlighted above) when I bridged this resistor with my probes or with another smaller resistor the audio sped up substantially and the pitch rose.

From here I removed this resistor using my de-soldering tool and attached two lengths of wire, one from each end of where the resistor had been. Once these two wires are in place you can begin experimenting with different potentiometer values to find the one which works best. I will often also experiment with a rudimentary voltage divider by attaching the third lug on the potentiometer to ground which often gives you a wider range of pitch though I did not have success with that method on this particular toy. I ended up getting the best results using a 1M linear potentiometer. With this toy I also found whenever the potentiometer was turned to too low of a resistance the toy crashed. I was able to solve this problem by adding a 47K ohm resistor along one of the wires leading to the potentiometer to stop the resistance from ever dropping below that point.

Apple - Pitch Bend WiringOnce you’ve soldered the potentiometer and resistor in place you need only to drill a hole, fasten the pot in place and secure the wires. Close up the toy and you’re done, you’ve now got a pitch bend knob to modify the pitch and speed of your devices audio output. During my exploration I was able to identify a few more possible bend points so next time we can start getting into those and perhaps find an interesting way to fill the extra hole I made on the left side of the above picture. Until next time, Have Fun!

Vtech Apple Part 3 – Voltage Starve

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