Re: LM324N op amp and toolchanger sensors

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Lance Hopper"
<snaggletto@c...> wrote:

> Hello,
> On an existing lathe and sensor circuit board I have 4x, forked,
> optical sensors and an LM324N op amp. This circuit is used to

sense

> the position of my tool turret. There are 6 output wires, 2 are
> power wires, and the other 4 are for each sensor.
>
> On my PMDX 120 breakout board, wiring to the inputs requires two
> wires, one into the input and the other into the common return.

With

> the optical sensors and LM324N, I will only have one wire for each
> sensor, no common return. How can I wire this to my PMDX 120
> breakout board to get the sensor input without a common return wire
> to complete the circuit?
>
> Is it possible that the - supply wire going into the sensor
> circuit board could be used as the common return for all 4 sensors??
>
> Any help would be appreciated.

Most likely the LM324 (single supply op amp) is used as a Schmidt
trigger (cleans up the signals from the opto's). Since an LM324
references everything to Gnd the signals will swing from gnd to the
supply voltage. If the PMDX card has an isolated ground on the
inputs you will either have to tie it to the supply ground (and loose
any isolation) or run the opto card from an auxillary supply with
it's ground referenced to the PMDX input ground. I was under the
impression that the PMDX card does not have an isolated input so you
should be able to just interface the 4 outputs back using the power
supply ground provided it is a 5V supply. IF the card runs on 12 V
then you you have a problem. You can't pump 12V directly back to the
parallel port. You will have to build an interface circuit. You can
use 4 NPN small transistors and run the collector supply from +5 or
use an open collector buffer IC to do the level translation.

The inputs on a Campbell card are opto isolated and you can use them
with 12V (or even 24) devices for postion sensing.