On 6/4/06, Darren Gibbs <tsquank@yahoo.com> wrote:

> When I hook up a scope to the +5V lead at the far end of the cable,
> it looks beautifully flat when nothing is connected.  When I connect
> a Sharp sensor, I start seeing 1V dips every 1ms.  Same thing when
> two are connected.  I also see ~1V pulses on the signal output every
> 1ms.  The data sheet says the Sharp parts update every 32ms, maybe
> they're sampling every ms and averaging?  I thought maybe the 1ms
> illumination pulses were pulling down the supply, but if the IR
> shines continuously that doesn't make sense.
>

I do not think the IR will shine continuously. Normally for photoelectric
sensors the emitter (normally visible red LED or infrared) is pulsed with
high current to get better sensing distance.

Clearly you want to have some local buffer for the power supply. Could
you power up the sensors with its own supply? At least put a big capacitor
near the sensor. Normally we put a relatively big low ESR capacitor
across the emitter circuits to buffer the peak pulsing current.

As for Mutual Interference (MI), that depends on the sensor. Some
sensors have good MI immunity, some don't. Most well-designed
photoelectric sensor should have good immunity against ambient
50Hz/60Hz light. HF light (modulated energy saving lamp) could
cause problems for many sensors.

Regards,
Xiaofan
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