Prison Door System Built Using Only Timers and Relays

Reddit user enticingasthatmaybe was recently contracted to build a system to electronically control the door and gate system of a southern prison without the use of microprocessors; not even transistors.

The reasoning behind this is that should the system fail, the prison trustees wanted it to be a simple enough to fix that any electrician could do it. The idea of it being difficult to hack was also a factor. The designer drew an easy-to-use chart that explains which part controls which section of the system. All a technician has to do is find the faulty part, buy a new one, and slip it into the socket.


It may be a more cumbersome solution than using microprocessors, but in a place such as a prison, practicality takes precedence over miniaturization and elegance.

In case things go really wrong, asenticingasthatmaybe explains:

There is a keyed interlock override switch that will complete the interlock logic if there is a mechanical failure. They specifically spec’ed the lock to be center return so it would have to be manually turned every time. (More incentive to have it timely fixed).

It’s certainly a niche market he works in, but it’s interesting to see that devices are still made in this way.


In addition to being an online editor for MAKE Magazine, Michael Colombo works in fabrication, electronics, sound design, music production and performance (Yes. All that.) In the past he has also been a childrens' educator and entertainer, and holds a Masters degree from NYU's Interactive Telecommunications Program.

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