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Sansa E200: current drawn through USB cable.

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saratoga:

--- Quote from: peter_s_d on April 08, 2008, 02:46:39 AM ---A 12 Ohm resistor was the smallest that I could lay my hands on.  When I get to a suitable shop I'll buy 1 Ohm and a 0.1 Ohm resistors for current sensing - or maybe a decent multimeter.  Also, I thought that a largish resistor might reduce the current to the compliant range, but something is (falsely) deciding that the battery is dead.

--- End quote ---

A resistor reduces current by introducing a voltage drop.  With a 12 ohm resistor, you are only supplying about 3v at start up, which is too low for the voltage regulator to handle.  If you want to do this, remove the battery so that it can't charge.  


--- Quote from: peter_s_d on April 08, 2008, 02:46:39 AM ---Compliant devices should not draw more than 100 mA before negotiation.  USB 2.0 allows negotiation up to 500 mA.  

--- End quote ---

True, but very few people seem to pay attention to that, and in practice hardware will supply 500ma without negotiation.  

peter_s_d:
Eevan,

0.5 Amps into a 530mAh battery sounds like a lot, but I guess that is the way that Sandisk designed things.  

Saratoga,

The start up current should be less than 100 mA which gives a voltage drop of less than 1.2 Volts.  It was just an experiment.  It turned up a surprising problem with the e200 where it reports a battery problem when it has a supply Voltage problem.  I don't know whether to blame the OF or the hardware.  Either way I'll live with it.  

I expect a _host_charger_ to supply 1.5 Amps, but sadly my PC is not a host charger.  

The e200 is known to have problems with many USB ports.  

I can confirm that my e200 had problems with my computer *before* I loaded RockBox.  It would repeatedly connect and then lose the connection.  Its behaviour seems worse when the battery is flatter.  

I'm trying to work out if it is possible to make an e200 with RF more standards compliant (and reliable) than an e200 with OF.  

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