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Sunday, June 27, 2010

CD controlled lawn mower - Hack a Day

CD controlled lawn mower

posted Jun 26th 2010 11:00am by Mike Szczys
filed under: digital audio hacks, repair hacks

[Oliver Nash] was enlisted by his parents to fix their robotic lawn mower. They owned a Robomow which happily navigated their yard to keep the grass at a nice level. These robots rely on a perimeter wire with a special signal running through it to ensure they are inside of the mowing area. Confronted by a dead perimeter module, [Oliver] ordered a new unit and disassembled the old module to study the components. He also measured the signal generated by the replacement unit. In the end he was able to produce a replica of the signal using audio software, burn it to a CD, and playback the recording using the perimeter wire. It’s a bit of a zany idea but it worked.

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A robotic lawn-mower


A few years ago my father bought one of Friendly Robotics‘s Robomows. The Robomow is a battery-powered robotic lawn-mower that will happily mow your lawn for you; all you have to do is charge up its battery and ask nicely. My father’s model is the RL550 and not only does it do an excellent job of cutting the grass but it emits a satisfyingly deep humming sound as it proceeds merrily about its work. Watching it work, one gets the feeling this is a mower that really enjoys its work.

The perimeter wire

Clever though the Robomow may be, it does need a bit of help figuring out exactly what it is that you would like mowed. To Robomow you are just as you are likely to want your prized Blue Bell Tunicate’s cut down to size as your are keen to have your grass cut.

Partial success

Let me begin by telling the story of a successful attempt to get Robomow to obey my discman.

I gathered my amplifier circuit, discman, signal CD etc. and went round to my parents’ house. There I set up my equipment, pressed play on my discman and turned up the volume till my oscilloscope (which I had also connected up to the perimeter wire) indicated appropriate signal strength. I then turned on Robomow and asked it to mow. To my absolute delight it complied! It began mowing, reached the perimeter cable at the edge of the lawn, turned correctly and continued mowing. After another pass across the lawn, it reached another edge and turned for a second time. At this point I asked my brother who was present to press pause on the discman. Instantly Robomow stopped and complained that the signal had disappeared. This was all great news. My python script’s CD track was controlling the mower. Success!

A calibration problem?

Although I was able to get Robomow to obey my signal, unfortunately I was not able to get it to do so reliably, at all. For the vast majority of my attempts, Robomow indicated my signal was present on its signal strength indicator but when asked to mow would think about it for a long time before eventually refusing. Unfortunately without taking apart Robomow (which I don’t want to do) very little information is obtained on each attempt. Not having Robomow obey my perimeter signal reliably is a little disappointing and I dare say I could overcome this final hurdle but having already spent a lot more time than I ever wanted to on this project, I decided it was time to write up and stop. My partial success was still fairly satisfying!


Pretty cool deal... the mower and the way he figured out how to control it in another way:) His Page is very detailed on how he did it too...


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