Perimeter switch

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How the Perimeter Switch Works

  • A European Robomower patent contains a description of how the perimeter switch works, along with schematics and waveform diagrams.
  • Oliver Nash's Discman Powered Mower blog post tells about his experience trying to replace a broken permitter switch. He shares a Python script to generate a similar audio waveform that he attempted to play through a portable CD player to control the Robomower.

Perimeter Switch Shut Off Time

Some old perimeter switches time out too quickly. Here is one possibility for a modification from Terry on Robomower Yahoo list...

There is one way to make it stay on indefinitely. One characteristic of the switch is that when power is applied, the switch remembers its state from before it was powered down and resumes in that state (on ot off), but it resets the timeout. A characteristic of the Robomower is that it will not respond to very short outages of the switch.

I experimented with my switch and found that if you interrupt the battery power for more than about 400 ms and less than about 1 s, it will reset the timeout, but the mower will not see the dropout. You may have to experiment to determine if the times are the same for your switch. So a circuit could be made that would interrupt the battery power say, every 2 hours, and the switch would never turn off.

If anyone is so inclined to carry this further, I would recommend using a 555 timer in an astable configuration and have it drive an switching device (a relay or maybe a transistor) to interrupt the power, the circuit could be made small enough to fit in the switch. I have not tried this and do not know at what voltage the switch will begin to complain about a low battery.

AC Power Adapter

Older perimeter switches had a power jack that could be used with a wall adapter instead of batteries. When the power plug is inserted, it switches off the connection to the batteries and feeds DC from the power adapter in their place.

Some users have removed the batteries and directly soldered connections from a six volt DC wall adapter power supply.

Multiple Zones, One Perimeter Switch

A simple toggle switch can be used to switch wires from multiple zones to a single perimeter switch. There is enough room in the perimeter switch case to mount a switch if it is not too large.