Operation without battery (GTA02)

Andy Green andy at openmoko.com
Thu Jul 24 00:51:51 CEST 2008

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Somebody in the thread at some point said:

| I also tried 2) and can confirm this. It sounds like it tries to power on,
| but does not have enough power. I think it is not so strange, since the
| charger cannot provide enough current. Remember that the PSU tries
| to power on everything at once, so you basically get the spikes from
| all the components at once.
| I think this was mentioned before. IIRC, the problem is that it is not
| possible to tell the PSU not to power on everything at the same time.

That's right, to start Freerunner needs a battery in and the battery
needs some decent charge left in it, for the reason briefly during
startup it needs to eat more current that it is allowed via USB.  It
causes a "brownout" at that time since the USB current limit does its
job well, it chokes and restarts repeatedly.

The source of that clicking noise is pretty amusing.  I spent days
trying to figure out where it came from.  I removed the mic and the
other transducers.  It's actually the ceramic caps we use, the ones that
get a high change in current during these events flex because the stuff
they are made of is piezoelectric.  If you press certain caps gently
with a probe the noise gets louder as it conducts the twitch to the PCB
better then.

- -Andy
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