Was it Elbert Smit who wrote on Wednesday 30 October 2002 16:33:
> Hello members,
>
> I'm trying to understand a specification, but it is not completely clear to
> me. Maybe someone can help me out. I have a current loop-a-like interface
> with optocouplers. This interfaces are not true 20mA current loop interface
> as familiar in the industry, but rather a current sensitive serial link.
I didn't make too much sense of this. Are you trying to use an optocoupler in
'analogue' mode, or pulsing it? If the former, forget it quickly. The only
way to use those things is as digital switches
>
> It specifies a maximum input current while in "inactive" state of some
> uAmperes. Is this figure based on the leak current of the used PNP
> transistor or is it based on other parameters?
Maximum current of WHAT? Remember the only conventional way of turning on an
opto transistor is through the diode. The transistor may leak (nA or pA) and
the first bit of diode current may have no effect; I expect the latter is
your uA figure
>
> For the transmitter on our side we use an optocoupler. Opto's do have a
> dark current of a few nanoamps. Do I specify such a small inactive current
> for our transmitter? Or do I miss something?
I certainly did ;-)
>
> Below a rather simple drawing of the receiver (distance is maximum a few
> meters). Transmitter on our side is a optocoupler transistor output.
> Pull-up resistor on the other side (receiver) with an CMOS gate (series
> resistor before the input).
--
Regards,
Declan Moriarty
Applied Researches - Ireland's Foremost Electronic Hardware Genius
A Slightly Serious(TM) Company
Without the optimist, the pessimist wouldn't know how happy he isn't
--
Author: Declan Moriarty
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