Everyone needs to have the nicest, greenest garden on the block (though it all the time appears greener on the opposite aspect). However no one of their proper thoughts really needs to do all of the work wanted to make their garden look excellent. That is very true relating to mowing within the summertime. The warmth, the sweating, the dear weekend hours wasted: yuck! It’s virtually sufficient to make an individual need to want away the attractive summer season days so {that a} thick blanket of snow can cowl up their troubles.
However as of late, there may be quite a lot of assist out there to the turf lovers of the world. Robotic garden mowers, as an illustration, are coming method down in worth — and a few of them even do a reasonably respectable job. They nonetheless price significantly greater than a comparable push mower, nonetheless. However with extra of them turning up on the second-hand market as of late, there’s a good probability of scoring one at worth.
The substitute {hardware} generates a fence sign (📷: eelcogg)
GitHub person eelcogg has observed quite a lot of used Robomow RX and RT sequence robotic lawnmowers, specifically, popping up currently. These are some very succesful mowers, however the bargains do have a really important draw back — they’re steadily lacking their base stations. These base stations not solely cost the mowers, however additionally they generate a sign that determines the boundaries of your garden (and any areas that ought to be averted), in order that your neighbors’ bushes don’t get an unwelcome “trim.” With out the bottom station, the Robomow is successfully ineffective.
Shopping for a substitute from the producer is an possibility, however not a really wise one. Alternative elements for these entry-level fashions are priced surprisingly excessive. The bottom station alone may set you again half the price of a model new robotic mower. After factoring within the worth of the mower itself, what’s the level of even shopping for used at that time? But tossing these in any other case completely good mowers within the landfill appears horribly wasteful.
So eelcogg did what hackers do and began reverse engineering the system. After connecting an oscilloscope to a working system and capturing the boundary wire sign, a waveform simply above 3 kHz at round 2 volts peak-to-peak was noticed. By experimenting with resistors, it grew to become clear that the unique base station was designed to push a gradual present (roughly 150 to 200 milliamps) by the perimeter loop. That present creates the magnetic subject the mower depends on to orient itself.
As soon as the sign was understood, the following step was recreating it with cheap {hardware}. This was performed with an ESP32 microcontroller and a trusty LM386 audio amplifier. The measured waveform, saved in a byte array, is regularly fed into the ESP32’s onboard DAC. The amplifier boosts the output sign sufficient to drive the boundary wire, and similar to that, the mower fortunately follows alongside as if nothing have been lacking.
By flipping the polarity of the sign, the information wire can be used to specify keep-out zones. That is useful if it is advisable shield a flower mattress or recent grass seed.
The long-term purpose of this mission is to pair the home made base station with a charging circuit so it behaves similar to the true factor: broadcasting the boundary whereas the mower works, shutting off the sign when charging, and toggling again when it’s time to mow once more. And with that, the worst a part of summer season could possibly be taken over by reasonably priced robotic assistants.
