CMU Power & 7.2v Circuit

[Mark McLeod]

Just an interesting addendum to the camera power cycling problem - the one where if it doesn't initially power up properly then you must cycle the camera power to get it going again.
We experienced a particular variation of this problem only once in Atlanta, and that was in the pits during a systems check.

For most teams a simple cycling of the robot power fixes the problem, however, if you are using the IFI backup charging circuit as is, then when the 12v source is cut off, and the backup power is off, the 7.2v battery leaves enough of a charge via feedback through the breaker panel into the RC that power to the camera is not cutoff when you throw the main breaker.
When this happens the only way to cut off power to the camera altogether is to disconnect the 7.2v battery (or try to figure out if it's legal to add a diode to block current flow back into the 12v circuits).

P.S. I edited slightly to try correcting the impression that the RC was purposely running off backup power.

[Keith Watson]

After turning off the main 12v supply, the reset button will turn off the 7.2v supply. This is in the manual.

[Mark McLeod]

After turning off the main 12v supply, the reset button will turn off the 7.2v supply. This is in the manual.
This is beyond the manual.
You seem to be thinking of how the reset button will turn off the RC when it's powered solely by the backup battery after you've cut the main power. The Master processor will also cut backup power after about 3 seconds. That's not the issue I'm bringing up here. I'll try to state the issue I'm warning about more clearly.

It's the interaction of the camera and the IFI backup circuit in particular that complicates matters in that when the main power is off, the circuit as designed (lacking a diode) allows power from the backup battery to bleed into the main breaker panel (there is no off-switch). From there it supplies power to the RC through the 12v terminals, bypassing the normal 7.2v power input.

At such low power the RC doesn't actually run (although you do get some faintly glowing status lights), but the trickle of power extends to the I/O pins.
This isn't an issue for most sensors, however, the camera receiving power from the RC pins seems to get just enough to prevent it from fully cycling the camera power. It's not usually noticeable and doesn't affect normal camera operation. I've only experienced it once in three competitions. It's only a problem if the camera doesn't power up the first time properly and requires a full power reset.

Most teams I've seen using the camera didn't incorporate a visible camera status indicator. We use a rapidly blinking light to indicate the camera is not working/communicating that goes solid when the camera is operational, so it was easy to see when the problem occurred and easy to diagnose.

[Al Skierkiewicz]

Mark,
I thought this would be a problem that would just drain the backup. I never thought it could back feed enough current to keep the camera up. A redesign with a steering diode is definitely warranted for next year.