NP25 Current Consumption / ucurrent

[Harald]

(10-11-2015 03:14 PM)TomC Wrote:  To those interested:

I've been 'using' one of the fine NP25 units from Jim Johnson.
[Thanks Jim Johnson / Chris Chung]

I've done some preliminary measurements using a 3V power supply and the uCurrent from Dave Jones.
[Thanks Dave Jones]

Current consumption is very close to 1.2mA - regardless of P/R mode or slow/fast mode.

Here are some of the modes:

1. 0.00 in display (wakeup).
2. Program running.
3. Full display (-8.88888888-88).

The ucurrent module makes these measurements most easy - including being able to view the transient nature of the current on an oscilloscope. I am using a ucurrent Gold which has bandwidth of 300kHz; it sufficiently shows much of the transient nature of the current draw. I will have to study the display/keyboard strobing to better understand the timing. I may work on a higher bandwidth current measurement too.

All for now,
TomC
From lovely/autumn Detroit, Michigan, USA, 3rd Stone.

1.2mA seems far to low. The problem with the hardware design is that there is no propper current limiting for the LEDs. The limiting factor is usually the CR2032. But that results in significant battery drain.
With the power supply it is probably the shift register that limits current.