Stalker V3 Power vs. V2.3

In my testing of a Stalker V3 I’m seeing higher power consumption than on V2.3 with the same arduino sketch when my code goes into sleep_mode_PWR_DOWN using the /avr/sleep library. I have now confirmed that the V3 uses 5mA in this mode while the V2.3 uses less than 1mA. I measured the supply current by measuring the voltage across a 1 ohm resistor in series with the battery pack with a DSO Nano scope on the 10mV/div. scale.

This current level is a big problem for me as I use the stalker with an XBee radio in cyclic sleep mode. I can’t afford this much battery drain when the stalker is doing nothing in the 4 minute interval between transmissions.

With the help of my friend Dr. Broad we tracked the cause of the extra power consumption to the new switching voltage regulator for 3.3V power which is now used instead of the two analog Micrel 5205-3.3 (KB33) regulators used on the stalker V2.3 and earlier. The problem is subtle and not surprising that it was missed. This regulator draws very little current when there is no current flowing through it but, as soon as even a small load is applied it starts switching between no current and 3mA with increasing duty cycle as the load increases until at a load of ~.3mA it is on full time conducting 3mA. At higher loads it continues to draw the same 3mA making its impact less noticeable for larger loads which this regulator was designed for.

Unfortunately when I power down the stalker while my XBee radio is sleeping the board current is in ~.5mA which is where the new Stalker V3 switching regulator burns 3mA. The regulator current thus reduces my battery life by almost 6x as a result. I will continue to use V2.3 stalkers as long as I can get them or until the V3 gets a fix. If low power and long battery life are not an issue for you the switching regulator works just fine.

Thanks for your good suggestion, we have mentioned it to our engineer and those would be considered in the next version.

Best Regards