Friday, July 10, 2015

MMS Photo-inator Xsi Initial Prototype Worked

The next phase of the MMS Photo-inator project was to complete the prototype.  I spent the afternoon and evening of July 3 working on the prototype.

First, I had to desolder a few more 2N6045 NPN transistors from the board I found on the hack rack at the Milwaukee Makerspace.  I needed two more transistors but I removed four just to have some spares.  I broke one of the feet off by wiggling it too much.  Putting the electrical plug under the board gave me the leverage I needed to pull the transistors off the board after the solder was removed.

The trick to removing soldered components from a circuit board is to, first, use flux to better transfer the heat to the board.  The second tip is to use copper desoldering braid to remove solder from the pins.  After removing the solder, the transistors come off pretty easily with a little force.

The next step was to add some small strips of wood to the board that the buttons were mounted to so it would stand up on its own.  I found some extra strips of wood at the Makerspace and attached them to the plywood.

Now that the board is ready, I needed to wire the connections.  Since I want to be able to assemble and disassemble the prototype easily, I decided to use terminal strips.  I attached three terminal strips to the board.  One would be used for the 12v power coming from the power supply to each light.  One strip would be used mainly to complete the 12v circuit to the collector on the transistors.  I also used one connection on that strip to connect the negative wire on the PSU to common ground.  The final strip would be used to connect the switches to the Raspberry Pi -- three sets of connectors for power in, and three sets for power out when a button was pushed.  I used either u-shaped or blade connectors on the ends of the wires to make it easier to connect the wires to the strips, switches, and lights.

After all the wiring on the prototype was done, I made ten connector wires to connect the prototype board to the breadboard for the Pi.  There are four terminal blocks on the breadboard to accept the connector wires.  One block is for the wires that send 3.3v from the Pi to the buttons.  One block is for the wires that receive the 3.3v back from the buttons.  A third block connects the lights to the transistors, completing the circuit.  The final block connects the ground wire from the PSU to the ground on the Pi.  Finally, I had to wire up all of the connections from the Pi GPIO pins to the various parts on the breadboard.  Here is the schematic.  It is also on SchemeIt at this link:

The final prototype worked exactly as I hoped.  The lights lit up and were bright.  The Pi recognized that the buttons were being pushed.  And, best of all, the Pi did not get fried.

Next, I need to work on the Python code and get all of the features working.