[IMSAI Guy] has an old HP 3488A Switch Control Unit that he wants to dismantle for parts ( see video below the break ). The 3488A is pretty simple as far as HP test equipment goes — a chassis that can hold various types of relay cards and is programmable over GPIB. He notes up front that these are plentiful and inexpensive in the used test equipment market.
Around the back of the unit is a card cage that accepts up to five option cards providing
- 4×4 matrix switching
- on/off SPST switching
- switching signals to a common bus
- VHF switching
- Digital I/O signalling
The teardown is an interesting glimpse into the solid engineering design of 1980s HP test equipment. The option cards are well shielded, and have an interesting back panel connector that breaks out the signals to screw terminals and provides strain relief. The brains of switcher was a Motorola 6809 and connectivity was provided by an Intel 8291A GPIB interface chip. The power supply is solid, and many of its parts can be reused on other projects, such as the transformer and a beefy 20W DC-DC converter by ST. [IMSAI Guy] also scores a bunch of latching relays from the option cards which will no doubt come in handy on future projects.
These kinds of programmable relays can be very useful when building automated test fixtures. There were other solutions for this as well, back in the day. Metrabyte ( bought by Keithley, bought by Tektronix ) was one company that made a whole line of switching interface modules that hooked up to your PC’s ISA bus. Omron also offered similar products. Have you ever needed banks of programmable relays for your projects? If so, let us know your solution in the comments below.