Direct output connections.

h3rk · 07-07-2008, 05:07 PM

There are three different output applications I am planning to implement, and they are all a little different. In each of them I am looking to pull a line low on a PCB, using a Brain's switched low side of a digital output.
Ignore the periods.

1. +5V-----10K----|-----10K-----IC
..........................|
..........................+----Low pin on FB Digital output
..........................|
.........................SW
..........................|
........................GND

and I figure since .5mA is <<< 200mA this will work.

2. GND----SW-----0 ohm-----BCM(IC)
.....................|
.....................|
.....................+-----Low pin on FB Digital output

I haven't torn apart the BCM in question, but I'm pretty sure the output current is low (the pin is spec'd at 5V/0V in the service manual)

3. This one's tough for ASCII, so I will refer to a drawing that I have up already.

I want to tie the collector of TR752 or pin 1 of comparator IC3 to ground with the low pin on FB Digital output.

10V /500 = 2mA

I think the max current per output is like 200A so I think that it is safe, but I put it out there for feedback, and as a potential example of things that you can do with the outputs, not requiring the use of relays.

h3rk · 07-08-2008, 01:37 PM

I guess the question is; will that darlington array bias correctly with something other than 12V on the collectors? If not, I suppose I will have to bias another transistor in my custom interface with 12V so that it (new transistor) turns on when ground from the output is switched, baised properly for sinking the 5V or 10V to ground.

Am I making sense?

greenman100 · 07-08-2008, 06:39 PM

At first glance, your approach would be fine.

h3rk · 07-08-2008, 06:55 PM

Cool, thanks for looking at it for me.
I'll get a chance to try it out in the next few days, I'll report back here on how it goes. I don't see much potential for overcurrent or any other bad events by trying it. I'm thinking worst case, they just dont work.

h3rk · 07-30-2008, 03:21 PM

Can I take the switched side of an output to ground, regardless of the state of the output, without hurting anything? + side is not used in this case (see above). Just making sure.