RA81 spindle sensor

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Sun Jan 18 11:46:17 2004

> The sensor appears to be optical in nature - with four wires (red,
> black, yellow and white).

Yes, I beleive it's optical. Most of these sensors consist of an LED on
one side and a phototransistor on the other.

_Often_, the emitter of the phototrasistor is grounded, the collector is
pulled to +5V by a relatively high resistor (>10k) and also goes to a
gate input. The LED has a low-ish resistor (a few hundred ohms) in series
and goes across the 5V line. So either one side of the LED is grounded,
or one side goes to +5V.

Can you see 2 pairs of wires going to oposite sides of the device -- one
set for the LED, the other for the phototransistor?

See if any of the wires go to logic ground. If only one does, it's a good
bet it's the emitter of the phototransistor, and it's pair will be the
collector -- the signal you want. If 2 do, then one is the emitter of the
phototransistor, the other is the cathode of the LED. See if you can find
the LED series resistor going to one of the other wires. The missing wire
left over is then the one you want.

 
> So:
>
> 1) Anyone know the connections to the device? If so we'll stick the

See above ofr how I'd try to figure them out.

> output side on a 'scope next weekend and see if it outputs anything (of
> course we have no working unit to see what the waveform *should* look
> like, grr)

Well, you know what frequency it should be (#holes in the sensor disk *
spindle speed). Look to see if you get a good waveform, swinging hard
enough to switch whatever it feeds into, at that frequency.

>
> 2) There are a couple of unknown-status RL01 and RL02 drives in store.
> Long shot, but anyone know if they use the same sensor in any part of
> their mechanism so we can do a temporary part swap with a (hopefully
> good) unit?

I don't think they do.

-tony
Received on Sun Jan 18 2004 - 11:46:17 GMT