Replacing existing pic

[Freman]

It would be mounted behind the screen - the back side of the screen is a flat black - haven't tested it's reflectivity.

The other alternative is to use one piece of shiny 'something' on the back of the screen at the bottom (where it doesn't bend) and use 2 detectors.

Which of these would you use?
* Phototransistor (Say: http://tinyurl.com/5bspbk for example)
* Photodiode (Say: http://tinyurl.com/58wuwp for example)
* or a full on IR Receiver (Like: http://tinyurl.com/54vqs6) and PWM the IR led(s) to the right frequency.

Edit: Oooh, just found the Sharp IS471F proximity detector... that could be nice - cept for shipping - I can pick the other options up locally...

[skimask]

Which of these would you use?
* Phototransistor (Say: http://tinyurl.com/5bspbk for example)
* Photodiode (Say: http://tinyurl.com/58wuwp for example)
* or a full on IR Receiver (Like: http://tinyurl.com/54vqs6) and PWM the IR led(s) to the right frequency.

Can't really say for sure. Phototransistor/diode would probably require a bit of 'lensing' to aim to light right, but you wouldn't need to be really accurate or anything. But...you might trip the sensor with the ambient light in the room, so you'd need to throw a bit of 'fuzzy logic' in the program, maybe a counter that say counts 10 times in a row it senses the light and kicks out whatever it is you want to kick out.
An IR TX/RX may have it's advantages...relatively easy to do, one obvious one being that you'd only be looking for the signal that you're sending out, fewer false triggers.
Either way you go, if you know when the IR is on, then you can sense if the IR is really being reflected vs. with ambient light, if you know the IR is off, and you're sensing the signal, then you know the room light is getting in the way.

[Jumper]

Hi,

Why not attach a sensor with encoder from an old PC mouse on the end of the rotating axis. Then you can count how many pulses and position your screen within mm from where it should be.

You might even have a pin on your pic to a hardware counter and then it will more or less count by itself.

/me

[skimask]

Why not attach a sensor with encoder from an old PC mouse on the end of the rotating axis. Then you can count how many pulses and position your screen within mm from where it should be.
You might even have a pin on your pic to a hardware counter and then it will more or less count by itself.

I thought about that too...but, if that count goes off by one this time, one the next time, and so on, one of those times, the motor is gonna drive too far, burn out, the screen is going to fall off, whatever. Still need some sort of end of travel sensor to reset the counter to zero (or 100 or whatever) once in awhile to keep things straight.

[Freman]

Actually the motor has it's own cut-out

When the screen is fully extended it kills the motor, and when it's fully retracted it does the same. That's built in the head end. The worse that'll happen is it'll extend to far for my use and knock something off the TV unit

I did consider it, and still haven't ruled it out (as a mouse is cheaper then my parts order - and I should have one laying around)

But I have questions like - how do I count without causing the remote to fail, or while still being able to respond on the serial port. - If I remember right
one of these timer/pwm/things/ works as a counter also - perhaps I can let it do the counting in the background and interrupt when it overflows.

I suppose it's one of those things I'd have to experiment with.

The option is open for a combination of the two.

A sensor at the top to tell it when it's fully retracted, and using the mouse sensor to count the way down.

But, just knowing absolutely whether the screen is UP or DOWN will be so much easier.

My biggest problem now comes from being completely broke and not being able to afford the parts I need to make sensors.