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Step 4Prototype - Displays & Drivers
I started by building a "self contained" Charlieplexed (read more about Charlieplexinghere) seven segment display unit with drivers and current limiting resistors. This little unit can be reused in other projects.
I decided to not waste any veroboard or labboard so I hot glued four dual-displays together and tacked on eight NPN transistors on them and then connected it all together using 0.1 mm (AWG 38) polyurethane coated wire. This wire is great to work with since you can solder right thru the insulation without stripping it first. I crank up my old Weller to 400C wrap the wire an turn or two on the component pin and the heat and apply solder. It's extremely time saving, but the solder joint looks like crap quite often due to the melted plastic.
After soldering it together and connecting it to a ten-pin header via nine current limiting resistors I manually checked it by applying VCC and GND on all pins in combinations and wrote the resulting lights on a grid I discovered that I had one bad solder joint and that I cross connected the wires to the first and last driver transistors. That was easy to fix and probably saved me hours of frustrating debugging the software for a non existing problem.
I connected the wires to a nine-pole molex header and reinforced the solder joints on it by applying hot glue to it. By putting the molex header on a cold harddrive and then applying the glue it was easy to get a nice glue-reinforcement.
I decided to not waste any veroboard or labboard so I hot glued four dual-displays together and tacked on eight NPN transistors on them and then connected it all together using 0.1 mm (AWG 38) polyurethane coated wire. This wire is great to work with since you can solder right thru the insulation without stripping it first. I crank up my old Weller to 400C wrap the wire an turn or two on the component pin and the heat and apply solder. It's extremely time saving, but the solder joint looks like crap quite often due to the melted plastic.
After soldering it together and connecting it to a ten-pin header via nine current limiting resistors I manually checked it by applying VCC and GND on all pins in combinations and wrote the resulting lights on a grid I discovered that I had one bad solder joint and that I cross connected the wires to the first and last driver transistors. That was easy to fix and probably saved me hours of frustrating debugging the software for a non existing problem.
I connected the wires to a nine-pole molex header and reinforced the solder joints on it by applying hot glue to it. By putting the molex header on a cold harddrive and then applying the glue it was easy to get a nice glue-reinforcement.
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