, I am building a control panel with a good sized lexan window in it..I want to put a proximity switch inside the panel behind the lexan... so that when someone walks up to the panel, the proximity switch operates (turns on an LED internal light so the instruments inside the panel can be read without having to open the door ( its wet, dark environment).
I could use some suggestions on what type of proximity switch will work in that application. I want to power it with 24 vac or 110vac and have it energize a relay coil or pass current to the light directly. I am trying to avoid 4-20 ma and a controller set up..
Could you perhaps use one of those IR motion-sensor switches? I'm not sure how well they "see" through a Lexan window.
All the proximity switches I've seen have very short ranges and don't seem to detect people well. If you had your operator carry a magnet, you could use a reed switch -but I expect that would be too much trouble for the operator.
The power consumption of most proximity detection systems will be more than the LED - so I would be tempted to leave the light on.. However..
Passive IR is going to be problematical through a window. It works by the the sensor dividing the covered area into sectors and so generally is better for a crossing target than one directly approaching in a path that may be right up one sector.
A (non-visible) break-beam optical system may be an idea - if you have something to stick a reflector on for the person to walk between reflector and box.
Or a non-visible laser diode beam and sense the reflected radiation.
A simple amplified microphone may be an idea - get the person to cough, or say the immortal words, " Where the f*** is the light switch?"
Basically, any of these will probably work - but leaving the light on and maybe having a hinged cover over the window if the light is going to be annoying at other times, is going to be a lot cheaper and more reliable.
If you really must, I would go for the passive IR but mount it to one side of the window, peering out of the box at an angle. That way you get a better chance that the person will cut through several sectors on the way and also, it won't obscure what is central in the window.
Try a cheap and cheerful unit intended to control outside security lights - it will have the relay built in. You can always remove the electronics and repackage them to suit your box - but don't forget the plastic window, which actually does most of the work in setting up the sectors.
You can make your own sector pattern for this, presumably, very short range application by setting the sensor at an angle and sticking some narrow vertical strips of tape (like a bar code, only a bit wider) on the bit of the window it looks through - that should insure the person cuts through sensor sectors as he/she approaches. It is the change in signal as they move from clear line of sight to the sensor to behind the taped bit that will trigger the unit.
OK now we are on the same page...that would be hot. I could put up a lable that says 'light switch' right in the middle of nowhere..then the person will say 'what the f***k ...this no switch' and the light will come on.....NOW that would be totally amazing. Funny as hell.
I wanted something tricky like yer mic idea...thats superb even better than a proximity switch because the victim will go into total shock that this thing responded to his complaint.
good idea...I could mount this outside in the rain too...it wouldnt have to be inside the box.
Thanks... the mic idea is the hottest... Id need a dinky mic I could insert into a tiny recess drilled into the plexiglass...and pin hole though the remainder of the glass for sound travel.. do you have some key words I can search to get the rest of the electronics the relay or board etc?
If you take the insert from a crystal microphone (thin disk of "crystal" with a couple of metallic areas with wires solderd to them) and super-glue it to the back (inside) of the (thin) window, it will use the window as part of the microphone and be very sensitive as a sound detector. Use superglue or any other hard adhesive and not rubber-based glue or adhesive foam pads, or the glue will mechanically isolate the sensor. Works extremely well glued to any large thin sheet (metal garage doors for instance, or metal lockers).
As an alternative, you can buy child's toys "Super Snooper" - which have a small plastic box with built-in microphone and amplifier and battery and a pair of headphones. In the UK they are sold for 1GBP and sold so that "You can listen in to conversations". They provide enough output to operate an opto-triac. Why build what you can buy for 1GBP?
Why not just install an Solid State Occupancy Sensor, they're usually used to detect people in office bdlgs to shut off the lighting circuits when there's no one around or in it....probably available in watertight configurations by now as well.
If I come across a Mfgr. I'll let you know. Honeywell comes to mind, but I've seen others way more sophisticated.
The mickey mouse approach could be amusing };-) as long as it turns on the light inside your panel., whatever is clever.