Hi everyone, in a nutshell I need to make a push/pull solenoid retract when a break beam sensor is broken that runs of a battery pack.
I have called Core Electronics and asked about this and the person I spoke to said they have all the components I’d need to do this but can’t help me put it all together and recommended I approach an engineering joint. I have a very limited understanding of what it will involve to make this but reckon it’s something I could do myself if someone was able to teach me.
I’d be happy to pay for the help and figured I’d put up a post on here before contacting an engineering place as if I can get this to work the way I need I’ll need a heap of them and if someone can teach me it may cost me in the short term but it’ll save me having to buy them from an engineering company ongoing.
I have kept what I need very simple and can elaborate on how this will be used if someone is keen to help.
Hi Jarrod
Welcome
Firstly does this exist or is it a new thing.
What part is battery operated, is it the solenoid, sensor or everything.
Your sentence
is delightfully vague.
What variety of solenoid are we talking about. You say “push pull”, does that mean you have to activate to go one way then reverse to go the opposite direction or has it got a spring return system where the solenoid has to be powered at all times to hold it in the operated condition.
Too many variables to start guessing. I personally have given up on that
Everything will need to operate from a battery pack.
Solenoid just needs to retract/pull back when the beam sensor is broken. Spring return is preferred.
Basically I am a trapper and am designing a new cage trap without a foot plate to release the trap door. The idea is that the solenoid pin will hold the door open. when an animal enters the cage and breaks the beam the solenoid retracts and the door drops.
Needs to run off a battery pack in the field.
I don’t have any good pics of a trap on hand to upload so these will have to do for now.
Do you have the list of components that were suggested?
I think it would look something like this:
The relay is used to convert the low power signal from the sensor to a level that will drive the solenoid. The power module is used to provide 5V for the sensor. I have assumed you will be making the case yourself.
The item that you need to confirm before starting is the solenoid - it must suit the trap you are planning to use. You can wire that up manually to make sure that part of it works before proceeding with the sensor. The second step would be to confirm that the target animal will trigger the sensor for long enough to release the solenoid (more than 1s).
Hi Jarrod.
Jeff has covered some things here to get started although suggesting a battery size at ths stage might be a bit premature I think.
Firstly the solenoid. The sizing here depend a lot on how much force is required to release the gate. If using a spring return type this might require a pretty hefty spring. Also to be considered is the current required to hold this solenoid. This is where the battery size could be a game changer. Another thing is that most solenoid do not like to be energised for extended periods. As well as depleting the battery they will get rather hot with the possibility of burn out. Spec sheets nominate a recommended duty cycle.
A better alternative would be a latching type as Jeff suggested. needs power to operate and needs power to release which is done with another pulse of reverse polarity. No battery drain from the solenoid between times. Adds up to a smaller battery but will require some electronics.
Another way which will save battery is to have your spring return solenoid but have a catch / trigger mechanism arranged so that when the solenoid operates it operates some trigger so releasing the catch and gate. The solenoid only has to operate while the gate closes. This would save the battery and the reversing electronics and while mechanically more complex electronically simpler.
Shame you can’t have it all. But there is a few things for you to think about. You are the only one that has access to the actual trap so the mechanics will be largely in your court but may not be all that difficult.
Cheers Bob
I did not suggest a latching device. The solenoid I suggested is designed to hold a door closed against a spring, or, for the OP’s use case, to hold a shutter open against gravity. When it is fired the door pops open or the shutter drops down. It does not require any reverse polarity. It is reset by closing the door or lifting the shutter to retain it behind the lock pin.
Thanks guys, so I guess the first thing I need to do is buy some solenoids and test them out to make sure they’re strong enough to retract and let the door drop?
If I buy them can I, for now, wire them to a battery with a toggle switch to test them?
The solenoid only needs to retract for a split second to let the door drop. If the animal moves, the beam is restored and the pin resets I will design the door with a smooth vertical length of metal so the door doesn’t get hung up on the pin and once closed the pin can then extend out to it’s normal position and act as a lock keeping the door closed. This is still an idea in my head that I need to make a proof of concept. Once that’s done, and it looks like a viable project, I’d then look to refine the system so that the pin retracts when the beam is broken, then stays out locking the door closed until a reset button or something is pressed. So then the solenoid isn’t being opened and closed every time the animal moves in the cage continually breaks the beam which will save battery life. Or have the system programed so that the pin retracts for a set amount of time (say 1 second) then goes back out until reset locking the door down.
Again, thanks for the help and I guess I’ll grab a solenoid and test it. I was thinking of getting this one to start with as I like the look of it and that it has mounting holes to secure it down
Yes - building it bit-by-bit will be easiest. A momentary switch would be closer to what the sensor would do, but the difference doesn’t really matter.
That feature was not considered in the above parts list, and it does complicate things somewhat. There is an electronic solution, but perhaps the preferable way to do it (because it is similar to the rest of the system) is to have a second sensor connected to another relay that detects the shutter closed and cuts off the power from the battery.
For sure! When I automated our chicken coop doors (to open and close with the sun), by far the hardest part was getting the mechanics working smoothly (but maybe that’s also because I am software first, electronics second and mechanics a distant third Fortunately, you have gravity on your side!
Given that you are not suggesting any form of remote monitoring or control, the electronics/electrics seems at least to me, the easier part. Base on the information to date, it is likely achievable using parts such as you listed plus a relay or two or a tad of electronics.
The solenoid you referenced seems like a good place to start. I like that it requires no coil current to stay locked and that you only need to active the coil for a short period and the job is done until later human intervention. When experimenting with the mechanics you can also consider things like: (1) whether you need it to lock the gate shut after it has sprung or whether gravity is sufficient (I guess it partly depends on the strength and intelligence of your target species) and (2) whether the chosen solenoid will survive the environment (weather, dust, bird poop, etc.).
Some thing to keep in mind.
Assuming the door/gate is sitting on the pin that needs to be removed, there will be a few ways to get the best result.
If you do it as a direct pull the pin, what ever device used will need enough power to overcome the friction of the weight of the door.
If you used the solenoid to “punch” a plate that pulls the pin out then the solenoid has time to build up speed (f = ma) so more acceleration = more force.
I think of this like a hammer. rest it on the nail and apply force until the nail goes into the wood and compare that to hitting the nail with the hammer…
Of course you can always at a laver setup (a long lower force movement gets transferred to a short high force movement)
Note: if your solenoid has more then enough power, no need to over complicate things… so this is just some thoughts.
My rough image
Hi Jeff
Sorry, I did misread that. I got as far as the “latch” bit and incorrectly assumed a “latching” solenoid. I did not consider a door “latch”.
And yes. If the gate is not too heavy it would only require a small protruding bit on the gate to sit on the latch to hold it up. Operating current only 0.6A also.
Cheers Bob
I have ordered a few things from core electronics including the latch solenoid, break beam sensors and snap switch.
When I get them I’ll test the latch solenoid.
If it works as I hope it will I guess the next thing I’ll need help with is assembling them to work together with whatever other components are needed (relays, power modules, battery etc?).
Again, thanks for the help and I’ll post again once I receive and test the solenoid.
There are many options available for the regulator and it is worthwhile to look through the list and select the one that best suits your requirements. Some regulators are fixed and some are adjustable, but 12V to 5V is very common so there should be plenty of choices from the fixed regulators and they are ready to go.
