# Scanning power budget – useful measurement technique explanation

This is a really good explanation from David.
Here’s the trace after Scan2560m12msNoLeds.hex boots between the 12ms pulses. The meter measures 85.8mV. The scope measures 88 mV.  MGL: So it’s good that they agree

There’s 2.8072V on one side of the 10 ohm resistor and 2.7215V of the other side of the resistor, or 0.0857V. This matches with the 85.8mV measured across it. The Nordic is seeing 2.7215V.  This is where the 2.72 comes from that he uses later.
I measured the 10-ohm resistor and it was very close to 10 ohms but contact resistance (no substitute for David’s experience) is a problem, so I assume that the resistor is 10.00000000… ohms. It’s not, but close enough.
Current: I=V/R=0.088/10=8.8mA constant.
Power: 2.7215*0.0088=23.95mW
So the program is soaking up a constant 8.8mA from something.  That’s clearly a showstopper.  On my Fluke, I see a constant 13.51mA when the program is paused.  When the DW turns on, and is just waiting for a command from the Nordic, the current goes up to 21.51 – exactly 8mA!
Here’s the 12ms pulse. The solid cursor is “A” and the dotted cursor is “B”. The pulse measured in the center of the rise and fall times is 11.8ms. The height is 127mV. The increase in current is 0.127/10 = 12.7mA. The power of the pulse is V*I=2.7215*0.0127=0.03456 watts. The energy of the pulse is 0.03456W * 0.0118S = 0.4078 mW-S=1.1329e-7 W-H.
There is that little pulse at the beginning of the longer pulse. I don’t know how to calculate it. For now let’s ignore it.  That’s probably some soft-machine processor activity setting up the radio for the next listen event. More troubling then the pulse is the 8.8mA the Nordic is drawing constantly. What is turned on (or what has been turned off might be a better way to look at it).
It could easily be the case that there are parts of the Nordic that are not turned off.   I need to systematically go through the init. process and see what’s still turned on.  How can we track down stray currents so I can know where to focus my attention?
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MGL: I assume that you are just measuring the Nordic current, and nothing else?

The solid cursor is “A” and the dotted cursor is “B”. The pulse measured in the center of the rise and fall times is 11.8ms. The height is 127mV. The increase in current is 0.127/10 = 12.7mA.

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The power of the pulse is V*I=2.7215*0.0127=0.03456 watts. The energy of the pulse is 0.03456W * 0.0118S = 0.4078 mW-S=1.1329e-7 W-H.

So I want to make sure I understand your results.
• 11.8 ms pulse seems close enough to 12 for government work. Good,
• The increase in current is 0.127/10 = 12.7mA.   — divide by 10 because of the 10Ω resistor?
• The advertising pulse draws 12.7 mA for 12ms
• Watts = volts x amps so

power is 2.7215*0.0127=0.03456 watts = 35mW.

• The energy of the pulse is watts x seconds = 0.03456W * 0.0118S = 0.4078 mW-S=1.1329e-7 W-H.
• So to make it more tangible…a CR2032 is good for about 200mAh at 2.8V so that’s  0.56 Wh (assuming it is not abused)
• So it ought to be able to scan 0.200  * 2.8 / 1.1329e-7 = 4943066.46659 times – assuming it was switched off the rest of the time.
• If scan requests were issued every second, that’s 0.200  * 2.8 / 1.1329e-7 seconds in days = 57.2114174 days.