RoboTank #3 / motor driver version 2

Here is the second version of the programmable motor driver.

It uses a L239D chip to drive two DC motors and modulate their speed individually.   The board can be controlled with only two input wires.  This is made possible through an interface program loaded in the ATMEGA238 (same as Arduino UNO) onboard chip.  The interface chip and the driver chip are running on two separate power circuits and both are in sockets and can be easily replaced or, in the case of the ATMEGA238 chip, reprogrammed.

Using the ATMEGA238 chip makes this motor driver very versatile since 10 pins (5 digital and 5 analog) are still available for inputs/outputs.  This driver can then be reprogrammed and customized rapidly.  Here is the etching pattern I made using ExpressPCB:

Finally here's the part list:

• 1x - Small copper clad laminate board
• 1x - 16 pins socket
• 1x - 28 pins socket
• 2x - 0.1uf capacitor
• 1x - 16MHz crystal
• 2x - 6 pins female headers
• 2x - PNP transistors
• 2x - Inputs Screw Terminal 3.5mm (2 pins)
• 2x - Inputs Screw Terminal 5mm (3 pins)
• 1x - L293D (or SN754410)
• 1x - ATMEGA238P-PU
• Some wires
• (optional) 1x - Heatsink for the L293D

I'll put up a Instructables ASAP with the PCB layout file.  Until then I can send it to you if you contact me directly.

RoboTank #2 / homemade PCB

This was my first attempt at making a PCB at home.  I follow this awesome tutorial explaining how to make PCB using a laser printer.  The first step was to design the board.  For this I used ExpressPCB free software.  Then I printed the design on a magazine paper.

The next step (which took me 3 tries) was to transfer the design to the copper plate using an iron.  This was a big learning experience about the necessary spacing between the traces and the amount of time to apply the iron.  In the end I got something that was good enough to go to the next step.

As suggested, I corrected the mistakes using a Sharpie pen.  After a Ferric Chloride bath here is the result:

I used a sponge to rub the surface during the etching.  Apparently the Sharpie fix is not meant to survive that kind of abuse.  This is still fixable.  The final step was to drill the through holes and do the assembly.