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pretty much an optical switch will work. the IH units actually use a small board inside the housing with what looks like a few resistors and the wire connections.
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Does anyone know what optos are used in the IH optical limit switches?
Regards,
Ray L.
pretty much an optical switch will work. the IH units actually use a small board inside the housing with what looks like a few resistors and the wire connections.
Not if you want high accuracy and good repeatability. And, the IH switches use dual optos, so you can have separate limits and home switches in the same package.Originally Posted by Runner4404spd
Regards,
Ray L.
HimyKabibble, do you need to replace some ? Didnt you get a set of switchs from a guy on the forum ?
I have a large quantity of switchs but they are a little diff than what I have seen in the IH switch boxs (you can look on BoB Warfields Blog and see the IH switchs) well infact he has pics in one of his threads.
I dont think the ones I have are duel though, but they are so small two could be run side by side. It would take a slightly different trigger arm than IH uses though. The slot on there switch is horizontal to the case to where mine will be vertical.. Really now that I think about it mine could be mounted under the rod/shaft with a simple trigger hanging down off the shaft so it would move through there gap.
The ones I have are 5v with TTL output and the half way test I have done show they would be very repeatable & accurate (although my test where not that good). I could send you a couple of them to test and try if you thought they would do you any good.
Here is a link to a PDF if it helps
http://media.digikey.com/pdf/Data%20Sheets/Honeywell%20Sensing%20&%20Control%20PDFs/HOA7720-HOA7730.pdf
These the circuit boards for them is inside of the housing
Jess
Jess,
Yes, I bought two of the IH switches from someone here, but I need several more. I want open-collector outputs so I can run higher voltage to improve noise immunity, and I like the idea of a dual opto, so both home and limits can be implemented in a single switch per axis. Also, the IH ones are known to have excellent resolution and repeatability, which is largely a function of the performance of the opto itself, so rather than "reinvent the wheel", I'd like to use the same ones, if I can find out what they are. Unfortunately, they're glued in place, with no visible markings.
Regards,
Ray L.
SO Have you contacted Gene or his boys ? Wouldn't that be where ya need to be inquiring ?
Don
IH v-3 early model owner
I have done that. Of course, they may not want to say....
Regards,
Ray L.
Is the IH a dual switch ?
I really didn't realize just how many different types there are. I will have to go through my collection ( I have a Hugh amount of them but I bet dual channel is going to be thin).
Not sure but is this something like you need ? Although I cant find any that is pre wired, all would have to be put on a board for wiring.
http://www.components.omron.com/comp...SX10310305.pdf
Jess
Yup, the IH switches are dualies, which is a nice feature. I looked at that one you pointed to, but my concern is it does not have a terribly sharp cutoff (look at the current vs shutter position graph). Some others have a much sharper cutoff. This can be somewhat mitigated by proper biasing, and feeding the output through a Schmitt gate, but I have no feel for just how well it would work.
Regards,
Ray L.
Oops! I took another look, and the optos are not dualies after all. It is two singles right next to each other. I've decided to go with the Omrom OPB941. It's got a small aperture, Schmitt trigger, open collector output. $7 each from DigiKey.
Regards,
Ray L.
Shew, LOL, you went straight over my head. OK so your saying there is a big difference in how fast the sensor can react, and I guess how sharp of a switching action it can have ( thin line that defines on/off).
I guess I kinda knew this but thought that for the most part they would be repeatable even if such things are true.
I would be very interested in seeing how you put two sensors together and how these are hooked up and used with a controller. I am afraid when it comes to electronics I am starting from zero.
I remember Aaron have a test rig setup to where he had the switches setup with a micrometer mounted on a piece of aluminum. His setup worked so good that when he got on the edge of triggering he could lay the assy down and it would un trigger just from the temp change from where he was handling it. Then without moving the micrometer he could touch the assy and the thermal change would trigger the switch. I guess he knew what he was doing & how to chose the right switch (sounds like you do also).
I found a link to his article of testing the limit switches.
http://web.archive.org/web/200502110...alhobbies.com/
Just go to the left side of the page, near the bottom, and the link to the article is there.
Jess
Jess,
Optos are not like mechanical switches - always either on or off. They have a range in-between where they are neither fully off, nor fully on. A run of the mill opto may allow you to move the flag as much as 2-3 mm before it transitions from fully off to fully on. During that distance, the PC may see it switch on and off several times, due to noise pushing the level just over the threshold. If you test it 10 times, you'll find the PC sees it switch at slightly different positions each time - not good. Getting the kind of repeatability IH does depends very much on picking the *right* opto (one with a very small "aperture", and a sharp cutoff characteristic, preferably one with a Schmitt gate in it to add hysteresis), and properly biasing it (setting the optimum LED current, picking the correct phototransistor load resistance, etc.) , so that range of uncertainty is minimized. The mechanical design also has to be very robust.
On mine, one switch will serve as the home switch, and be wired directly into Mach. The other will be the limit switch, which will be wired directly to the servo controller, and cut AC power to the servo power supply if the limit is hit. This will, of course, necessitate a manual over-ride to allow the system to be powered to back it off the limits. But, in actual use, these limits should *never* be hit.
Regards,
Ray L.
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