sid@lamont.ldgo.columbia.edu (sidney hellman) (01/25/91)
I was wondering if anyone can help me with the following problem.
I am currently working on a project to control pneumatic
valves via an existing computer output module. The module outputs 24
volts to open, and ground to close the valve. I also have solenoid
valves to operate my pneumatics. This systems works as expected.
The problem is that I am now building a control/manual
override board to be placed between the two units mentioned above. I
plan on having an overide switch and a bicolor status LED. The IDEAL
wiring would be:
******
input * *
---------- *
* -------------------------------------------------- output
24 v---- * |
* * _____|_____
****** | |
on-off-on toggle switch green /\ two wire bicolor LED
\/ red
|_________|
| 560 ohm
|_________/\/\/\/\/\____ 12 v
As I had FEARED might happen, when either the computer tries
to close the valve or I put the toggle to the neutral position the the
output floats to about 9 volts, which is enough to open the valve. I
guess this is what happens when one makes assumptions about what one
is buying.
Anyway, I would like a simple method to have my LED's sense
the status of the signal line with a higher input impedance. Any
ideas would be welcomed. I would like a simple idea, if available,
due to size of the project (40 valves).
I am working on this problem here, but maybe one of you could
help.
email or posting, what ever is preferred.
Sid Hellman
sid@lamont.ldgo.columbia.edu