[IMSAI Guy] has an old HP 3488A switch control unit that he wants to disassemble for parts (see video below after the break). The 3488A is pretty straightforward as far as HP test equipment goes; chassis that can hold different types of relay cards and is programmable via GPIB. He notes upfront that they are plentiful and cheap on the used test equipment market.
On the back of the unit is a card cage that accepts up to five option cards
- 4×4 matrix circuit
- enable/disable SPST tripping
- connection of signals to the common bus
- VHF shutdown
- Digital input/output signal
The Teardown is an interesting look at the robust engineering of HP test equipment from the 1980s. The sample cards are well shielded and have an interesting rear panel connector that shunts signals to the screw terminals and provides strain relief. The brain of the converter was a Motorola 6809, and communication was provided by an Intel 8291A GPIB interface chip. The power supply is robust and many of its parts can be reused in other projects, such as the transformer and the 20W DC-DC converter by ST. [IMSAI Guy] also collects a bunch of latching relays from option cards that will no doubt be useful in future projects.
These types of programmable relays can be very useful when building automated test equipment. There were other solutions for this before. Metrabyte (bought by Keithley, bought by Tektronix) is a company that made a whole line of interface modules that plug into your computer’s ISA bus. Omron also offered similar products. Ever need banks of programmable relays for your projects? If yes, let us know your solution in the comments below.