Intermittent digital signal when PWMs are used

[EricVanWyk]

I'm betting that it is an intermittent short downstream of the DSC. The DSC's power supplies are designed to gracefully handle short circuits by shutting down their output until the short is cleared (rather than dumping large currents through it). Try wiggling each of the connected wires to see if the 5V or 6V lights blink.

[Alan Anderson]

Originally Posted by EricVanWyk

I'm betting that it is an intermittent short downstream of the DSC.

That wouldn't explain why disconnecting the PWM outputs makes it better, would it? The missing BAT light in particular hints strongly at a faulty "upstream" power connection.

[EricVanWyk]

Originally Posted by Alan Anderson

That wouldn't explain why disconnecting the PWM outputs makes it better, would it? The missing BAT light in particular hints strongly at a faulty "upstream" power connection.

Hmm... Good point. I think I misread something, and I think I agree with you.

The PWM power is powered by the 6V rail, which is independent of the 5V rail. However, the PWM signal is powered by the 5V rail... but there is enough output impedance so that hard shorting every single PWM signal to ground wouldn't be enough to short the 5V rail. I had forgotten about those resistors!


EDIT: Scratch that last theory.

This sounds like you are fantom powering the DSC from the cRIO. I (now) strongly agree with Alan that your connection to the battery is bad.

[Al Skierkiewicz]

Michael,
We haven't asked yet, but you do not have any jumpers in place on the PWM output do you?
I would attack this by getting a voltmeter and measuring the input voltage at the DSC connector. It should read about 12 volts with a good battery in place and the correct polarity. Place the robot on blocks so that the drive wheels are not touching the floor. Run the drive while you are measuring the input voltage. If it falls to anything less than eight volts, then move your meter to the PD output and try again. If the voltage at the PD remains at 12 volts then you have a high resistance connection between the PD and the DSC. Usually this is a badly made connection in the DSC connector. Use new wire and remake the connection. If the voltage at the PD is low and the Crio is not rebooting, then the connection to the WAGO on the PD is bad. Often this is due to incorrect stripping of the wire. Wires for insertion into the PD should be stripped 1/2 to 5/8 inch. If the voltage at the PD input terminals is low (Usually the Crio would be rebooting), then check for bad terminations at the 120 amp circuit breaker or the PD terminals and wiring and try replacing the breaker that is feeding the DSC. On rare occasions, the main circuit breaker is bad. Try substituting a new one and see if things improve. The final possibility is you have two bad DSCs.

[michael714]

People,
You are awesome. I goofed up big time here. We were fooled by phantom power from the cRio. The DSC had wires from the distribution panel, but the wires were attached to the 5V output. Oy!

After going back to the docs, it was obvious that the DSC was miswired. We now have 12volts going to the DSC and all 3 lights are lit. I'll let you know if this fixes our intermittent line sensor.

Thank you so much. Sorry for the sloppy mistake.

[michael714]

Yes. This did fix the intermittent signal. We probably won't repeat this mistake (too many more times). Thank you again, all.

[Al Skierkiewicz]

That's why we are here.

[Matt Krass]

Originally Posted by michael714

Thank you so much. Sorry for the sloppy mistake.

Don't worry about it, it wasn't a mistake, you just learned one way not to wire a digital sidecar!

We like to help, otherwise they put us back in our cages.