While experimenting with various alternate power sources for a JeeNode, I was curious as to just how low it could go in terms of voltage and still function as a simple wireless transmit node.
Made the following mods to push things a bit more than usual:
- adjusted the fuses to set the brownout level to 1.8V iso 2.7V (efuse: 0×06)
- changed the RFM12B’s low-battery level to 2.2V iso 3.1V (rf12_control: 0xC040)
- removed the voltage regulator from a JeeNode, and keep just the electrolytic cap
- changed the radioBlip sketch to run at 8 MHz, i.e. 16 MHz clock % 2
This is the same setup as with the Tiny Lithium discharge setup described a few days ago, BTW.
Here’s the JeeNode-under-test (JUT?) – the cap I used here is again 100 µF:
One pair of wires is from the power supply, the other from the multimeter.
And then it’s just a matter of hooking it up to a power supply and gradually lowering the supply voltage.
And the result is … 3.0, 2.9, 2.8, 2.7, 2.6, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.85 Volt still works!
Anything lower than that and the sketch stops sending out packets once a minute – but then again, that’s probably just the brownout detector of the ATmega kicking in!
To get it back up, I re-connected the power supply at 2.1 V and the node started its blips again… lower didn’t work, my hunch is that the RFM12B’s clock circuit needs that slightly higher voltage level to start oscillating.