Hey Folks,
We’re having a strange issue where we get intermittent true and false on our digital I/O port, but only when PWM cables are plugged in (to the same digital sidecar). When we unplug the PWM cables, the intermittency goes away. And we get the intermittency whether the line sensors are plugged in or not, so it’s not the line sensor causing the problem. Also, we’ve tried to different digital side cars and we get the same results.
Michael,
Most teams only use one Digital Side Car. Are you sure that you have a good connection to +12 volts on the DSC? Are all three LEDs on the DSC lit brightly? Are you plugged into the PWM outputs or the relay outputs? Are you using a premade 37 pin connector or one of your own making?
I assume all the digital sidecar power lights are a bright solid green: batt, 5v, 6v.
The battery is fully charged.
It sounds like a low power condition, possibly a short which could be on any of the connections. The addition of PWMs might just be drawing the power lower.
We’ve never used more than one sidecar, nor thought of splitting functions between them.
I agree on the power issue. Do you have a multimeter/voltmeter?
If you could measure the voltage between the +5V and GND pins on one of the digital inputs (any of them should work) while the PWMs are on and you’re seeing this intermittent problem, and while they’re off and everything is working, that may help us diagnose this problem better. Best bet would be to take multiple measurements, just to be sure we get a good one. Also, if you could measure your battery voltage while you’re at it, that info would be helpful too.
Hey Folks,
Thanks for all the replies. We are not getting all the lights to light up. On one sidecar we have no battery light. On the other side car, we have no 6 volt light. We have several batteries of various ages and several battery chargers. Does anyone have a suggestion for how to tell whether a battery is no good (apparently voltage is not a great indicator)?
Sounds like it may still be a connection issue. Just to clarify, do you have two sidecars hooked up at the same time or did you try two separate ones, but only one at a time? If both hooked up, it could be a power problem but it seems strange that it would happen with so many different batteries. If it’s one at a time I’d expect to see the same symptoms on both if it was a battery problem. I would check, check and recheck the connections, and the voltages across the +5V and GND pins still.
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.
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.
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.
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.
