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Simplicity is beauty: Teardown of an old garage door remote

Posted: 04 Aug 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Telectron? garage door? remote control? RF? teardown?

These days, sophisticated home-automation systems with smartphone-enabled, Internet-connected functions such as garage door control are regarded as "routine." Of course, it wasn't always so, but smart engineers worked some design magic with far fewer options, yet still did clever work.

This became clear to me when I came across an old garage-door remote control by Telectron, also called a clicker.

It has no date markings, but I estimate it is 30-40 years old, based on the design and asking some questions of family members. There's no indication of frequency, but due to the "Model No. T80-RF 230" designation on the back, and some similar units I found on the web, I assume it's a 230MHz unit. The package is 10cm x 5.5cm x 2.5cm thick and has only one user control, a large square push-button which actives a small switch on the PCB. It's the genuine embodiment of simplicity of operation, that's for sure.

Garage door remote

Garage-door opener is a model of simplicity in design and use; it has just one user button, with a large arrow moulded into it.

Compared to today's RF units that operate from 900MHz for a basic dedicated unit to 2.4GHz and higher for a smartphone connection, it is both easy and tempting to dismiss the design of this RF unit as trivial. However, the available parts were larger, design and layout tools were non-existent, and units like these had to be very, very inexpensive.

The design uses a simple one-transistor LC-resonant tank to set the frequency (no crystal); this can be adjusted as needed since the capacitor is a variable trimming type consisting of five interdigitated metal semicircles each about 8mm in diameter, and 6mm long overall. I didn't see a separate inductor, so I think the large wire loop serves the dual purpose of being the LC inductor and the antenna, a nice touch.

Garage door remote

The design and layout are typical of mass-market low-end consumer RF circuits of several decades ago, with few active and passives and a wide-open layout and PC board tracks, using through-hole components on a single-sided board.

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