Go Down

Topic: Is it time to mow the grass? (Read 185 times) previous topic - next topic



I want to make a sensor & reflector use light levels to determine if grass has grown high enough to mow, based on how little light can make it back to the sensor.

- So imagine a retroreflector (hard or take/sticker) mounted low on a tree/post/whatever.
- A bright, directional light source, like a red led (example).
- A CdS sensor (light sensor).

Periodically, the sensor would kick on, and a few pulses from the laser diode would fire, and the level returned (to be differentiated from ambient) recorded. What is interesting/convenient is that the sender/sensor and reflector need not be the same height over the lawn. This makes mounting options more flexible, as the lower to the ground a μC housing and sensor are, the more prone they are to interference and other environmental nasties. 

Over time, one would figure that less light would be returned as more blades of grass got in the way. By comparing the levels with grass height, it should be possible to tell when a good time to mow would be. 

Problem solved:
Mowing too often, or not frequently enough, as rain & sun do not operate based on a calendar. "Every 2 weeks" doesn't take into account positive or negative growing conditions.

Right now, everything is easy, except for a cheap retroreflective target for the LED laser diode to point at...


P.S. For those who don't know, "Retroreflective" does not mean 80s fashion. It means that like prismatic reflectors on things like the moon, a light shone on it from any direction will be returned to that same direction. This is different from a normal mirror, where the reflective light needs to be from a specific direction. Some call this a cat's eye effect.
"A wise man can learn more from a foolish question than a fool can learn from a wise answer". ~ Bruce Lee.
"If you drop it and it breaks, it was good." ~ Mr. William Lehr, my Electronics VoTech Teacher, on testing vacuum tubes. RIP


Modulated IR (38kHz) and a 3-pin receiver seems more appropriate outdoors than a laser and LDR.
Aiming an IR LED is also much easier than a laser.
See this thread.
What sort of distance are we talking about (twice the distance for a reflector setup).


Sep 21, 2020, 02:35 am Last Edit: Sep 21, 2020, 02:39 am by JCA34F
Manufacturers who make industrial optics (like Banner), sell those (corner reflectors).



With a 50mm reflector, the grass detection near the reflector can be 50mm off.
You don't have that problem with an IR LED and 3-pin receiver at opposite ends.


With a 50mm reflector, the grass detection near the reflector can be 50mm off.
Black paint!  :smiley-lol:


How about a microphone? When the grass gets long enough for it to "tickle" the microphone, its time to mow.

-jim lee
PNW Ardiuno & Maker club
1012 9Th Street, Anacortes, WA 98221 (Around the back of building)
GITHUB -> https://github.com/leftCoast

Go Up