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external battery "OFF" read in robotC 
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Joined: Sat Oct 25, 2008 12:18 am
Posts: 19
Post external battery "OFF" read in robotC
We are having some serious 'external battery "OFF" problems. We've done a lot of work to debug, including limiting NxT cable lengths to motor controllers. To do this we had to put two controllers on one sensor port on the NxT and two controllers on port 2 of the NxT. We also use a sensor MUX with two sensors and 3 - 90cm cables (one to the MUX and one to each sesnor), which is legit according FTC forums, however Hitechnic (makers of the motor controllers) support thinks it is still one of our problems. Unfortunately, we are still getting an occasional error even with the the SMUX unplugged. A

Anyway, here's our request...we want to know how to read the external battery voltage on different sensor ports, BECAUSE sometimes when we get the external battery "off" symptom we get the message (when it occurs on the motor controller attached to sensor port 1 (S1)), but when it occurs on one of the other motor controllers (?or maybe on the SMUX?) we get no message, but the motor controllers on that side are unresponsive. We've found a command to read the external battery voltage in RobotC, but it appears to only read a controller attached to the S1 port. Is there a way that we can read the external battery voltage on S2, S3, S4??

BTW - Hitechnic support thinks that having motor controller ports whose NxT cable daisy chain length approaches 90 cm is a PROBLEM! There is NO amplification in the motor controllers, it is just an NxT cable splice, essentially.

thanks, Chuck


Tue Feb 12, 2013 1:02 am
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Joined: Tue Feb 19, 2013 4:11 pm
Posts: 8
Post Re: external battery "OFF" read in robotC
The SMUX and the motor controllers are both run off seperate external power sources, 1 for the motor controllers (separate battery + wiring), 1 for SMUX (comes attached to the SMUX). None of these are powered by the NXT battery so changing how many ports you use on the NXT has no effect.

Since the SMUX has it's own power source I have no idea what your problem there is.
The HTSMUXreadPowerStatus function returns a boolean if your SMUX power is on or off.

However, I think your problem motor controller lies in the fact that you made your power circuit in series rather than parallel, which would cut down the voltage to each consecutive motor controller until it gets none at all (depending on power usage in the earlier ones)


Wed Feb 20, 2013 5:37 pm
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