Management of Power Management ;)

Svetoslav Trochev sal_electronics at
Mon Aug 24 04:15:33 CEST 2009

Ben Wilson wrote:
> Svetoslav Trochev wrote:
>> Ben Wilson wrote:  
>>>>> 5. SHR suspend, GSM on: 0.08A
>>>> This one looks strange, guys measured it to be ~45mA with uSD
>>>> inserted and
>>>> ~25mA without.
>>> I measured ~45 / ~25mA most of the time but on two occasions I did see
>>> ~75mA, i couldn't reproduce it though.
>>> You do see some weird things current wise when gsm is on during
>>> suspend.
>>> Psi.
>> I think I need more accurate meter here. My old Fluke 23 is only 3 1/2
>> digits and don't have needed resolution. I believe that suspend mode is
>> failing to turn off some of the hardware in my case. I have not upgraded
>> the firmware on my GSM module. Because the SSH connection between the
>> Neo1973 and the host PC is dropped when the Neo is suspend I will need
>> to connect the serial console to see the messages. Do I need to do
>> something special to enable debug messages on the serial console or just
>> connect the debug board?
>> Thank you Psi,
>> SAL-e
> ya really need an oscilloscope to measure the current with GSM on, as
> changes too much for a normal DMM to give an accurate reading.
> I was using a scope across a resistor when i did my measurements.

Oh yes. I would love to have oscilloscope, but right now I might will
able get my self a new DMM. If I get hold of something like Fluke
289/287, or 87V. I think one of them will do the job. Especially models
28x has data logging and graphs so we can monitor the change over boot
time-line in to the addition of min/max/avg. Let me look around if I can
rent one because I believe the price is in $500+ range for these puppies.

> Problem I found was the voltage loss in the wires and resistor at peak
> current. The phone kept shutting off due to low voltage.
Yes, That is why I used my 10A range, because the internal shunt
resistor of Fluke 23 was about 0.1 Om only, if I remember correctly. And
in addition I have only 1.5% + 2 counts accuracy so using for measuring
the Neo1973's stand-by current is not appropriate at all.
> Ended up making this with some nice and thick wires.
> The contacts I used are out of an old Nokia phone (phone, not battery).
That is really cool setup you have. I am going to build my self
something like that also! :)
> Even then I sometimes had to short out the shunt resistor until it had
> booted up and suspended.
> Psi.

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