pcb design - Method for assigning unique per-board addresses

We're designing transmitter/receiver boards for an RF remote-control application. To avoid talk between mismatched pairs, we want unique per-board addresses. The address is specified to encoder/decoder chips through 8 address pins.

We'll probably assemble a small batch (about 25) by hand, but will have the PCBs professionally fabricated.

What's your favorite way to do unique per-board addresses in a situation like this? I've pondered DIP switches, jumpers, and cutting/jumpering traces. I'm leaning toward cutting traces, but I'd like to hear what more experienced people typically do.

Answer

I'm surprised nobody mentioned EEPROM. We've had to put unique numbers in products a bunch of times, and most of the time they have gone into the processor's EEPROM or sometimes reserved locations of program memory. This is usually a simple thing to do as a final step of the production test and calibration process. Once the unit is deemed working and any calibration has been performed, the production test system sends a command to the micro to give it its serial number, or uses the programming interface to write the serial number in the appropriate location directly. Sometimes the HEX files that is programming into the micro is a one-off modified from the master template HEX file with the unique serial number for that device, with checksums and possibly other information modified accordingly.

A few years ago I was working with a company that was producing 100s of thousands of little thingies a year via a contract manufacturer in China. We sent two complete test systems to the Chinese manufacturer. The test program would maintain a serial number file, and we could send them new files to configure the units for new serial number ranges. All went well enough for a while, until one day we got units with duplicate serial numbers. It turns out the Chinese did something stupid with one of the systems so that it wouldn't run anymore. Instead of telling us, which they had strict orders to do if anything went wrong, they did a complete disk copy from the working system to the other system. This of course copied the serial number files and current state too, so from then on both systems handed out the same sequence of serial numbers. That was a pain to unravel.

I got to design newer test systems, so I made sure the serial number range and current state was kept in a EEPROM in the tester hardware and didn't provide any documentation about that to the manufacturer. We had about a dozen of the tester boards made, and we carefully assigned separate serial number ranges to each. When the manufacturer needed to be updated with a new block of serial numbers, we sent them updated tester boards. So far this system has worked very well. It also makes it easy to produce the occasional unit back here or at a different manufacturing site. Each place has its own tester with its own serial number range, and only one person was the master keeper of the serial numbers and would assign new ranges to testers. You could then pick up any tester and use it to provision units without having to worry about serial numbers.