[Cumulus] Some Cumulus experiences

[Peter Turczak]

Hi there,

Hendrik Hoeth wrote:
>> 
>> I think partially loaded it works ok. In this case it was plain empty
>> and rejected to boot when connected to external. I have a separate 12V
>> lead battery with a self build 5V adapter. It had worked before and
>> worked fine the next day, so I think my adapter is ok.
> 
> Are you sure the N810 _charges_ on that adapter, or does it only run
> without actually charging the battery? I tried a 5V supply first, and
> while it would run and draw current, it refused to charge the battery.
> Turns out that the Nokia chargers actually supply a slightly higher
> voltage, around 5.1-5.2V if I remember correctly. So I changed my DC-DC
> converter and voila, it works.

While building my own adapter for the N810 I stumbled across the same problem. When the current of the adapter is _not_ current limited the Nokia devices will consider it a "special" cable. See http://www.herjulf.se/solar/charge-station/Nokia_2-mm_DC_Charging_Interface_Specification_v1_2_en.pdf for details. The N810 expects a source resistance of about .5 Ohms. I cracked open a cheap 3rd party charger and found a .56 Ohms/1W resistor in line with the +5 Volts ;). 
I used four parallel 2.2 Ohm resistors to have enough heat dissipation. 

Fliegergrüße,
  Peter