Colin,

For tilt, can you use a single turn potentiometer?  If you can mount the
knob to the rotational pivot point and keep the body of it fixed, you could
get degrees from the PIC's ADC.  Just attach the wiper pin to the pic's
analog in pin and vcc and ground on the other two pins.

You may want to use a limit switch as a failsafe or even a stop signal.

I know it's moving slowly, but with position feedback you can implement a
simple position based ramping to control speed and avoid overshoot.  

The speed would be "cut down" based on the actual position compared to the
target position (aka position error). The closer the actual position is to
the target position, the more the motor speed would be slowed down.  Very
cheap components and pretty easy to implement.

Good Luck,
-Jeff

 
 

> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
> Of cdb
> Sent: Sunday, August 23, 2009 5:35 AM
> To: PICLIST@mit.edu
> Subject: [EE]Position Sensor thoughts.
> 
> I've been asked to design some electronics for a device that moves a
> tray from the horizontal position to a 45 degree position left and
> right of horizontal.
> 
> The person already has the apparatus and a standard 12v DC motor and
> operates the device manually at this moment. I'm providing other
> requirements and this has been thrown into the mix.
> 
> I'm toying with the following as cheap and not requiring too much
> after market fixing as sensors for detecting the top of the 45 deg
> swing to stop the motor via a Pic.
> 
> The motor will be moving slowly - I'm not sure how slow, but it moves
> eggs so I would think hospital lift slow!
> 
> Tilt sensors - when it reaches the correct angle the little ball
> either makes or breaks contact - I think break would be better.
> 
> Microswitch  - worried that long term positioning might be a problem.
> 
> Reed Switch - I reckon this would be the easiest to fit and cheapest.
> 
> Opto Switch - Either with cam or just blocking a LEd.
> 
> Bearing in mind that I haven't the faintest idea what the contraption
> looks like and that I won't be able to get my hands on one to play
> with, does anyone have any thoughts on my ideas?
> 
> Thanks
> 
> Colin
> --
> cdb,   23/08/2009
> 
> --
> 
> 
> 
> 
> colin@btech-online.co.uk
> 
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