Apple

VTech Apple Part 5 – 555 Trigger Oscillator

Sam

circuit bending, loop trigger, 555

I have to admit for some time I have been stalled with my Vtech Alphabet Apple circuit bending project. I love the toy aesthetically and have always felt like there should be more bends available then what I was able to find. However even after hours of experimenting and dissecting this toy I was left feeling somewhat underwhelmed with the results. Over the weekend though I brought it back out determined to turn it into a more functional instrument, and to do that I needed to create a trigger oscillator.

If you want to get caught up before going forward don’t hesitate to visit my previous posts on this toy:

VTech Apple Part 1 – Kill Switch and Line Out

Vtech Apple Part 2 – Exploration and Pitch Adjustment

Vtech Apple Part 3 – Voltage Starve

Vtech Apple Part 4 – Body Contacts

Since I hadn’t had any luck finding a loop on the board I moved on to less straight forward methods. I decided what I needed was a way to send a signal at repeating intervals to one of the contacts on the button matrix to trick the Vtech Apple into thinking a button was being repeatedly pressed and trigger a repeating sound. By generating this signal independently I could manipulate its frequency and control to suit my needs.

Once I had a clear definition of what I needed to get the job done the solution seemed all to clear, what I needed was a 555 timer. By setting up an astable 555 timer as a trigger oscillator I could route the square wave signal into the button matrix to repeatedly trigger the button (or buttons) of my choosing. Further by using a potentiometer I would be able to adjust the frequency of the square wave and therefore control the time between button presses as needed.

555 astable
This is a simple mock up of the circuit I used. Note that for this to work the positive voltage must be supplied by the toy itself and the ground must be share with the toy as well. This is easily accomplished by running the power from either the positive power connection on the Apple’s circuit board or directly from the kill switch installed in Part 1 . Just ensure it is connected at or past the kill switch so that the kill switch will remove power from the oscillator as well. Similarly the ground can be connected to any ground point on the circuit.

Astable 555 circuit
After testing my plan using a breadboard I put together this small 555 timer circuit on a scrap piece of perf board I had laying around from a previous project. I did my best to keep everything as small and compact as possible as my space inside the toy is somewhat limited. I’ve seen some circuit benders using what is called the “Dead Bug Method” in these situations to further minimize the size of the circuit. When building a dead bug circuit the components and connections are soldered directly to the pins on the IC rather than onto a piece of perf board. This can be an excellent way to shrink the circuit for those really tight fits but also leaves you with a more fragile product so since I could get away with using a board in this toy I did in order to get more stability and durability from the circuit. I will revisit dead bug circuits in a future post but in the interim there are many demonstrations of the method on YouTube if you deem it necessary.

Wiring 555 Oscillator
Once I had my 555  trigger oscillator circuit built the next step was to install it in my Vtech. I started out by planning positions and drilling holes for the potentiometer, switch and LED. Once these were in place I began the process of wiring the leads I had left on the 555 trigger oscillator circuit to their respective locations on the toy. On the diagram below I have marked the approximate paths of each wire upon installation. In planning this mod I did my best to limit the number of wires crossing between the back and front sections of the toy as these wires tend to get put under a lot of stress when the toy is being opened and closed. To achieve this I pulled power from my kill switch and sent ground directly to the negative terminal on the battery box. Since the switch and pot are mounted on the back portion this means only the pulse out wires have to cross over to the front half of the apple.

Wiring Vtech Apple

You may also notice that there are two pulse out wires leading from the switch to the button matrix. I used a 3 position on-off-on switch for this bend which allowed me to send the pulse to two locations based on the switch position (as well as nowhere in the off position) By connecting the opposing sides of the switch to different positions on the key matrix I am able to choose between two different buttons when running the oscillator. If you were so inclined and had the space to work with you could take this even further using a rotary switch or patch bay to allow you to select where the pulse was being sent. If there is a specific key you are after which you are not finding by touching the pulse to the solder points on the matrix try using your probe to connect sets of two points on the matrix together. If you find that this is necessary to get the input you desire this can be done by bridging the two points with a transistor and feeding the pulse into the base (more on that in a future article).

Finished Vtech Apple Loop
Once everything was wired I secured the 555 circuit and LED with hot glue, taped down all the loose wires and closed up the toy. I have to say after playing with it a bit I am really enjoying this modification. I’ve been able to produce a host of strange noises and effects and without having to use a hand to continually press the buttons I feel like I’m finally able to take full advantage of the other bends on this device. I’ve been having particular fun using the power starve to produce glitches in conjunction with the continuous oscillating noise produced by raising the rate of the 555 to high frequencies.

That’s all for today but I hope you guys have fun. Happy soldering!

Vtech Apple Part 2 – Exploration and Pitch Adjustment

Sam

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