I’m not getting the battery life I expected from the Nordic FOB.
The battery only seems to last for 400 or 500 button pushes, which is about 1 day in my application. Batteries cost $5 each, so I think I think it’s worth making sure there isn’t some “low hanging fruit” for getting more out of each battery.
Is the expected battery life?
Has anyone done an analysis on how much energy is used each time a FOB button is pushed?
Thanks,
Dave Thomas
I’ve used a nordic FOB for 6 months now, albeit not extensively but I’d say at least a few thousand presses minimum and never changed the battery yet. I can give it some finger bashing tonight and see what the cell voltage is to see if it is at all near its end, but I can’t see it being drained.
It’s pretty simple to work out though, you have an ATTiny on board which you can get the datasheet for and see the operating amps, as well as the nordic 24L01+ datasheet for transmission amps, and then the full program to work out how long it is turned on for and what it is doing so you should be able to accurately calculate the life time.
I’d say you possibly have an old batch of cell batteries that are close to their expiry date and the leakage current has almost drained them already.
Yup, I think I know how to do the analysis. But, I thought I’d ask first if it had been done before asking.
Power consumption is probably dominated by the 24L01, so it’s probably just a matter of knowing its power dissipation during transmission and figuring out how long it’s transmitting given the message size. But, I’ll check the processor power too, just to make sure its neglible.
Definitely not old batteries. Brand new and replacing in the actual application daily (they last about 1.5 days) Four batteries so far.
Same FOB though. I have three total, so I’ll see if current drain is different among the three.
I originally thought the buttons might be sticking sometimes and keepinng the FOB out of the sleep state. But, after reviewing the applicaiton code, I’m sure that would have been easily reconizable in my application.
Thanks,
Dave Thomas
Dave, can you hook up a lab supply at 1.5V with a 10 ohm resistor and measure the voltage across it at an oscilloscope?
I have an oscope, but it’s not digital (or a storage scope).
So, I don’t have a way to do a one shot measurement.
That would be ideal, however…
Dave Thomas
Analog scope + dark room + digital camera with long shutter time on tripod = storage scope 
But first you could check the dc quiescent current with a DMM, it should be in the few uA range.
I believe the amount of time (thus power) that the transceiver is ON depends on e.g. interference and signal strength since the transmitter keeps retrying for a certain period until it gets the message across.
Interesting idea to use a digital camera and analog scope. I’ll give it a try this weekend.
I don’t think there is any acknowledgement, based on what I see in the FOB source. At least it looks like auto-retransmit and auto-acknowledge are turned off.
The FOB is sending a four byte payload, but I’m only using one byte. So maybe I could get better life by changing the FOB code to send a one byte payload?
Also, the FOB code keeps the transmitter enabled for 3 milliseconds. Maybe I can reduce this time with a smaller payload to save power?
Thanks,
Dave Thomas