Since it costs almost nothing to run another test while I’m in bed…
I found another Tenergy battery that had never been used as far as I could tell. It had the solder tags on the ends. I charged it up and ran another test.
The fresh battery measured at 4.2V. The battery measured 1.42V when the test finished after 14465 seconds/ranges. Towards the end of the test (around 14300) the ranges started getting progressively longer, ending up in the 1.7m region by death. But that’s just during the final 3 minutes, or almost 4 hours.
14300 decent ranges.
3575 3D location fixes.
Assuming each range is the median of four samples, then we get 894 fixes.
Thoughts from David
1) The 5V to 3.3V regulator on the EVK1000 is a TI TPS73601DRB analog regulator with a 0.075V dropout voltage. It won’t make any accommodation for battery voltage less than the operating voltage of the DW1000.
2) The lithium batteries are getting old and might have high internal resistance so when the DW1000 is ranging it might be drawing down the battery voltage a lot. But maybe not. The capacity might not be (certainly isn’t ) what it was when the batteries were new.
3) The Eval board is drawing other power, like for the display. The board probably isn’t designed for lowest power consumption.
4) The coulomb counter wasn’t counting coulombs because current wasn’t flowing through the sense resistor so the 11000 number isn’t valid. The display read less because the battery voltage was lower – so the situation is actually worse. Probably most of the 21000 coulombs is gone. But since the battery is at least partially worn out some of the coulombs that went is weren’t available to come out, because the energy was lost as heat (probably).
If we want to do a “real” power test we need the modules working with a proper switching supply powered by these supercaps I have. This is another reason to fab a PCB.
Conclusions from Mik
This clearly wasn’t a well-controlled test, in almost any respect, but it gave me a feel for the challenges we are up against using the DW. The little lithium that David bought for the TS06 has 240mAh capacity, so we are only talking 225 location fixes.
Of course, allowing the battery to recover a bit between fixes, and not needing to sample over 4 fixes could make 4x difference.
That’s not an actual show-stopper if one can choose the ranging opportunities with care. How many times in a day do we actually settle?