Hi everyone - newbie here looking for some advice.
I'm trying to build a sheep clamp - think a venus fly-trap if you like. Essentially, it will hold sheep so that treatments etc are much easier to perform. Basically like this:
My first issue (I'm sure there'll be many) is what sort of sensor to use. We must be able to move the sensor easily - as we're working with young sheep and older sheep and the catch position will change. It will obviously also need to be able to deal with a farmyard environment.
At the moment I'm thinking ultrasonic but I'm not really sure. I would be really grateful for any advice anyone can offer. I can't find any info about what sensors the existing systems use.
I've done quite a lot with ultrasonics, including some experiments with "what reflects ultrasonic well". Basically a sheep seems like the absolute most-absorbing 'surface' possible except an open window.
Infrared would work well. These units work well and are fairly water resistant:
This is a pair: One transmits a modulated IR beam, the other detects it.
Thanks Terry - looks a cost-effective starting point.
I was thinking about going for a diffuse IR sensors - simply because it would make adjustment 'in the field' easier. Is this an option? If the channel the sheep were running though was 400mm wide, would I be right to look for a 300mm sensor so I didn't get false positives?
Also, is there any real difference for my purposes between an IR emitting sensor and a red LED emitting sensor?
Sorry for all the questions. I think I probably will end up going for the 'beam break' emitter/sensor setup as you suggested but just wanted to check out the other options.
Reflective sensors or any type don't seem like a good choice for a Wool Coat. But you can do some testing with a sheepskin. The beam pair can actually be tested simply with 5v power: green to ground and red to +5 volts on both transmitter and receiver. The Transmitter LED should light all the time. The Receiver LED will light when it is NOT receiving and is blocked from the transmitter. The Receiver led will go out when the beam from the transmitter is received.
Sunlight can be a problem for any optical sensor. The IR ones have good sunlight rejection, and putting a short round tube on the receiver is know to make it even better.
Optical and ultrasound may get dirty and stop working because of that, especially on a farm. Other than that, I was thinking of break beam sensors for this application.
Or how about a pressure sensor aka a scale? Sheep look fairly heavy to me, so when one steps on a scale you can easily detect that. Won't be as precise location wise, though.
Thanks for the jokes. The primary reason for building this is so I don't have to spend as much time working with the bloody things!
I think beam break is probably the way to go for some of the sensors, however, one side of the venus fly trap will move and adjustment of the width etc is going to throw the alignment off. I might try a cheap diffuse sensor - and if it doesn't work go beam break there also.
A pressure sensor was a thought of mine but I'm not that keen on it if I'm honest. It's probably going to be easter before I start building, but I've been stuck in the house for a week so been doing some homework in the meantime.
When I was looking at the video you posted, it seems the sheep are really close to the walls of the device. A break bream sensor will work fine if placed at the correct location.
Alignment is a bit of a problem, but then think about a TV remote: those are not exactly directional, either. Make both your transmitter and receiver have a nice and wide cone, and a small change in alignment won't be an issue. The sheep are big enough to block your sensors.
If you have the problem of sheep with very different heights, you may consider using two sensors, and just react to any of the two being triggered.
