Saturday, January 31, 2009

Computer Revision 1

While I was waiting for my batteries I also finished up the first computer revision. I plan on making a more advanced version but figured I'd do a basic setup which will give just what I need to get things rolling and then later, with the car mobile, I can test and prototype to see exactly what I want.

I figured the basics I needed were to monitor the RPM signal from the motor and relay this to the tach gauge and EPS system. I also wanted to make sure I could watch the temperature of the motor and controller. I can also added an output port so I could optionally install a small LCD screen to show this information although I haven't used it yet (just using a connected laptop currently). This version uses a BASIC Stamp microprocessor. I'm using an ADC0831 to convert the signals from the LM34 temperature sensors to a digital output. This sensors will output 10 millivolt per 1 degree F. The only other IC on the board is a 5v voltage regulator.

Below is a picture of the basic circuit board after it was etched. I've done chemical etching myself but for something critical like this I wanted it done professionally. I used ExpressPCB for the job. They offer free software to download which is very easy to use. It's not very advanced compared to other PCB software but will do basic jobs like this. After you design your board you can click an option to compute the cost of the board. There are a few options. You can get everything from prototyping to full production work. Below is the prototyping board. I think it cost $50 or so and you get three boards in case you mess up something while soldering. The prototyping version requires the exact board size shown below. I think it was 2.5" x 3.2" or close to that. It goes up in price considerably for full silkscreening and solder masks for surface mounting. After I placed the order, completely through the software, I received the boards in the mail within 3 days.

I guess I didn't need the flash here. This is just a loose fitting of the components. Yep it all fits.

Here is a shot of the board with all the components and IC sockets soldered in.

Added the BASIC stamp chip and ADC IC.

Here is a project box I picked up at radio shack. Turns out it's just a little too deep to fit where my original ECM was and I need to replace it later. For now the access panel is still off and I'm going to live with that way under the car is rolling and I have time to go back and clean things up.

Here is the finished box. You can see the serial port I added so I can update the software and tweak anything later. There is an external LED to show power and an external fuse for protection.

The computer is in the car and working as expected. That's it for the computer until revision 2.

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