Shortcut Saves Time at Plant

I once worked at Eyedentify, a company that made retina scanners for biometric security. Manufacturing was starting to ramp up production, so a burning room was built to cook the scanners for reliability.

We decided to use a small paper cup with a simulated retina pattern over the binocular-like eyepiece. Pressing the sole front panel button invoked a "scan," which was a motor-driven, infrared, near-field optical radar.

They asked me to build some boxes that would simulate a key press about once every minute. The unit would then log transactions. I used a 555 timer IC to drive a small relay. After I built two boxes and was starting the third, I realized that the burn-in room could hold 10 or 15 units. I did not relish the thought of building that many widgets.

I thought about it and realized that what we were mostly trying to accomplish was to check optics. I talked to our firmware guru, Bill, and we thought the Motorola 68000 microprocessor had some room in its ROM for a hidden routine. I told Bill to call the key-pressed routine once a minute, and do a loop once an obscure key sequence was detected.

At the same company, we had several models of scanners. The sales folks had to change firmware sometimes to fit the application, which could be networked or standalone.

I had used a trick on my Icom R7000 radio where you replace the SRAM with a larger one at the add-on circuit to swizzle the upper address bits. This took my R7000 antenna from 100 channels to 3,200. Note that it is really convenient to have a PC interface -- otherwise it takes a long time to program.

I got the same EPROM 27256s and used the Data I/O to stack two-code versions in one chip. I ran the upper address line to a small switch on the rear panel. Now the sales crew could flip the switch and reboot, and the unit would work for the other model.

This entry was submitted by Steve Lindberg and edited by Rob Spiegel.

Steven Lindberg has loved electronics since got his first Weller soldering gun when he was 12. He has 35 years of experience in test, debug, and design. His personal lab is 950 sq. ft. room with 350 instruments, from femto amps to a 40V 70A Sorenson, DC to 20 Gig.

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