Hedge Court Robots

• Color Pong
• Overboard
• Philly
• Symet
• Sandwich
• Roverbot

Homemade PCB Prototype

As part of building Philly, I wanted to make a homemade Printed Circuit Board (PCB). I've never done this, so I thought I'd try a prototype first. I chose to make a relatively simple ATtiny26 development board. Its mostly a single-side board, with a few jumper wires routed to the top layer where necessary. Read on for a description and photos...

Special thanks go to two people, Tom Gootee & David Cook. I relied heavily upon their excellent websites for ideas, instructions, & techniques for homemade PCB fabrication. They turned a hugely intimidating project into a breeze.

ATtiny26 Dev Board Features

1. Power Switch
2. Battery Connector
3. LM7805 Voltage Regulator - with decoupling & bulk capacitors
4. Power-indicator LED
5. ATtiny26 microcontroller - with decoupling capacitors
   • Reset pin connected to VCC with pull-up resistor
   • Momentary push-button switch to pull reset pin low - this is configurable via a 2-pin jumper connector, it can be disconnected if PB7 (reset) is to be used for regular I/O.
   • PA7 has an LED and current-limiting resistor connected to VCC (set the PB7 low to illuminate) - this is also disconnectable via a 2-pin jumper.
   • PA6 has a momentary push-button switch that can be used to pull the pin low - this is also disconnectable via a 2-pin jumper.
   • Both Port A & Port B have a 10-pin header (8 port pins, plus VCC & GND).
6. And finally, a 6-pin header for in-system programming. I use either Atmel's STK500 or AVRISP for programming via this port.

• Schematic - plaything.sch (in ExpressSCH format) or playthingSchematic.pdf
• PCB Layout - plaything.pcb (in ExpressPCB format) or playthingPCB.gif

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Photos

My first exceedingly poor experience transferring toner onto copper with Blue Press-n-Peel...

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Another shot of the failure, including the Blue stuff...

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Then I tried Staples Photo Paper, which was outstanding, and here I am soaking to remove all of the paper. The toothbrush helped speed the process. I scrubbed as hard as I could and there was no damage to the toner...

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A close-up of some paper remaining to be removed...

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Sweet looking board with toner transferred in beautiful detail and all traces perfect with no paper remaining...

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The board descends into the murky depths of Ferric Chloride...

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After etching is complete, and with the toner still on the board. You can see at the top a circle I drew with resist ink (aka, industrial strength sharpie marker) to test out how the marker would work. At the left you can see a trace that came out crappy so I touched it up with marker.

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Final board after copper was etched and toner was removed with Acetone...

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Complete board with components & battery & Atmel AVRISP, top view...

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Complete board with soldering done, bottom view...

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Nice view of the final board...