photomicro sensor, ~$25. Will this work for home switch?

[spoiledbrat]

I found this in the MSC book O' goodies, and I was wondering if it would function as a home and limit switch with mach 2.
Link: http://www1.mscdirect.com/CGI/NNSRIT...PMPXNO=1943178

just in case, it is item # 54048061

It seems to me I could place this on the undercarriage of my small gantry machine, with a small tab that would interupt the light when I am about 1" from the mechanical limits of my machine. I do have a 5v/12v power supply, but I am a blatant fool when it comes to this electrickery stuff.

Would this switch give me better repeatability (as a home switch) than the standard mechanical microswitch?

Thank you
Rob

[CNCgr]

I think so. At least I'm going to try it because you can make it coolant-proof. If you enclose it in a watertight enclosure and have a rod sticking out (sealed with an O-ring) with a tab on the other side I think it would work better than a microswitch.

[ViperTX]

The problem is that this will require some additional circuitry before you can sense whether it's on or off. The other problem is that the lens for the photodiode can become dirty if you're cutting anything that produces a bunch of dust....stick with a microswitch.

[Al_The_Man]

At $22.00 that's damned expensive for a slotted photo detector, you can get Sharp and others for $1.50 (Digi-Key etc), you may have to add a 2n7000 to switch a relay etc, but if it is just TTL input and you you don't need indicator light etc, its a cheaper way to go.
Al

[spoiledbrat]

Thank you for your responses. I thought I was black listed for a week or two there...

Maybe this info adresses the concerns brought up:


Excerpt from MSC: Transmissive sensing heads in standard, L-shaped, T-shaped and close-mounting configurations match most applications. Wide 5-24 VDC operating voltage range makes these photomicrosensors compatible with TTLs, relays and programmable controllers. Wire selectable Light-ON/Dark-ON output operation. Operation indicator for easy monitoring. Output Specifications: 100 mA load with 0.8 V residual voltage; 40 mA load with 0.4 V residual voltage when driving TTL. Response frequency: 1kHz (3 kHz typical).



Al, does this answer the concerns raised over this particular model?
I bought a power supply from A. Duncan that puts out 5V to power the switch, can I then send the output of this sensor directly into my DB25 board?

The design of my gantry router will keep the dust out of these well. Also, if it does get dusty, it will be wired so that the gantry stays on the machine (Dark-on).

PS: 1. What kind of repeatability is everyone getting from their switches?
e.g. 0.1", 0.01", 0.001", etc
2. What kind of switch is it?
3. What is the basic cost of that setup?

[Al_The_Man]

It has a few built in features over a discrete opto-slot sensor, but these features could be added quite cheaply, the unit shown has some conditioning circuitry that probabally squares the signal up and has either TTL direct in or will operate a relay if required and has an indicator. The same could be put together for under $5.00
(2) It is a infra-red transmitter/photo-sensor type detection switch.
Al

[CRFultz]

have you considered using a prox switch? They don't care about contaminents (unless your cutting metal) and they are available with a very narrow sensing window that makes them very accurate. I have 9 of them on my machine and they work great.
Chuck

[drk]

Chuck

Just wanted to know what was the connection diagram for the prox. switches.
Most I found were tooo large in size, expensive( $20) and work on 12V or more, while the cnc softwares used by hobbyist usually require a simple operation at 5V

[pmurray]

I too think these are kind of expensive.

Here's a link to a page full of choices of tabbed/untabbed, wide/narrow slot and a wide range of current draws - most are under $1.00.

http://www.jameco.com/webapp/wcs/sto...egoryId=151050

plm

[spoiledbrat]

"have you considered using a prox switch? They don't care about contaminents (unless your cutting metal) and they are available with a very narrow sensing window that makes them very accurate. I have 9 of them on my machine and they work great.
Chuck"

How accurate/repeatable will these be? I would like to think it is possible to set my machine up such that it will "home" at a specific location, plus or minus 0.001" or less. Am I dreaming out loud on this?

[miljnor]

I am using a 2-$5 microswitch and it zeros to within .0003-.0004 each time. Although for microswitches i think the wear/out factor is more of an issue. and if you want it sealed you have to make your own box. The optical switches or the prox switch are probably as good as the micro.


The microswitch is definitely the cheaper rout. but backlash is my limiting factor.

[bkukowski]

is there already a schematic for using a prox switch or a photosensor posted somewhere?