Beta Board Part 1

These directions apply only to the BETA Cupcade units. Most users can refer to the simplified final design on the “Interface Board” page.
It’s a tight squeeze, but everything just fits on a 1/4 size Perma-Proto board!

The Perma-Proto circuit is neatly divided into two sections. The left side is a basic audio amplifier for the speaker. The right side interfaces the analog joystick to the Raspberry Pi’s digital-only GPIO. The line down the middle connects the two ground rails across the board.

This diagram shows a rectangular Pi Cobbler; we’ll actually be using a “T” cobbler. Same functionality, same pins, just a different shape than shown here.
The Perma-Proto is turned around, with the labels upside-down. It’s fine, this orientation just makes our circuit easier to lay out.

Cut a wire a little over 2 inches long and strip the ends. Run this along row 9 between the two ground (blue) traces.

Aside from joining the ground traces, this provides a nice visual separation of the two unrelated parts of the circuit. It’s okay if this wire is a little longer and doesn’t lie flat; strictly a visual thing.

Make certain you’re connecting the ground (blue) traces, not one or both of the positive (red) traces.
Install five 10K resistors (brown-black-orange) in the positions shown, immediately to the left and right of the ground wire. Two go on the left (audio) side, three on the right (joystick) side.

The two resistors at the top connect to the positive (red) trace, while the two at the bottom connect to ground (blue). The final resistor bridges the center gap on the right side.

Bend the resistor legs so they’re parallel like staples, insert them into the Perma-Proto board so they’re sitting flush and then bend the legs on the back outward to hold them in place for soldering.

After soldering, the legs can be trimmed close to the board. Save these trimmings for the next step — they make handy jumpers!
Eight short jumpers are now installed in the positions shown in pink. Most of these are very small, joining adjacent pads. We can use the un-insulated clippings from the prior step because no other conductive traces are crossed.

Install these similarly to the resistors: bend each jumper into a small "staple" shape, insert it through the correct holes (triple-check!) and bend the legs outward to hold for soldering.
Six more jumpers are now installed as shown in pink (prior steps are gray). Because these jumpers cross other traces, they should be cut from insulated wire, do not use the resistor clippings for this step!
This diagram shows where the TS922 amplifier and LM339 comparator ICs will be installed later. In their place for now we’ll install sockets, then add the chips after everything else is complete.

Make sure you get the 8-pin socket in the correct position — it’s inset by one row, not right at the edge of the board.

Note that the chips will be installed “back to back,” with pin 1 facing opposite edges of the board; they’re not oriented the same way.

When soldering sockets, use only enough solder to make a good connection between the pins and vias. Don't keep adding solder…you'll fill the socket holes and won't be able to insert a chip!
Three more jumpers are installed, cut from insulated wire.

These wires cross over the IC sockets. Do not follow a straight shot as depicted in the diagram — that’s just to make the connection points more clear. The wires should actually be a little longer and will get bent around the sockets, so a chip can still be inserted.
Install the 100 µF capacitor in the position shown.

In the photo, notice the wires now bent around the sockets. Don’t add the chips yet, we’ll do that later, after the rest of the soldering.
This is a good time to pause and double-check your work.
  • Do your wires and components match the layout precisely as shown? Count the number of wires and components and the spaces between them.
  • Are there any cold solder joints or shorted pads on the back of the board? Now’s the time to repair them.
  • Are all the wire ends trimmed?
If something is installed wrong, at best the circuit won’t work as expected. At worst, the Raspberry Pi won’t boot or could even become permanently damaged!

The circuit is 5 Volts but connects to the Raspberry Pi’s 3.3V GPIO pins. Won’t this fry the board?

The LM339 comparator outputs are open drain. When active, they connect to ground (0V). When inactive, they “float” (aren’t connected to anything) and the Pi’s own pull-up resistors register this as a 3.3V “high” signal. The unregulated 5 Volts (which we really need for the amplifier) never gets back to the Pi…assuming it’s all assembled correctly, so please double-check everything!
Last updated on 2015-05-04 at 04.27.56 PM Published on 2014-04-04 at 11.56.13 AM