I appear to be getting 7mA current draw when the MCU is in sleep mode. This is not good. Even if left in sleep mode the battery would die in about a week. This is obviously where my power loss issues lie with the wireless sensor nodes. It should be microamps and not milliamps when in sleep mode.
I have a suspicion it is something to do with the Lowpowerlab sleep functions. Maybe they are not optimised for use with an ATMega328p.
I just wish I had an oscilloscope so I could measure the current correctly. I’m using just a cheap multimeter at the moment which isn’t great.
What I will try next is to use the Lowpowerlab library for control of my radio, as the Jeelib library hasn’t got great support for the RFM69CW as it is optimised to use with the RF12B radios, and the Jeelib library for the sleep functions. I will see how that effects the power loss.
On suggestion from Andrew Lindsey on Twitter I’ve switched to the sleep functions on the LLAPSerial library from Ciseco. I’ve got it running with 2 second read/transmits again so I can compare it to the power loss using the previous library. Let’s see how this goes.
Initial tests look promising. After running for 12 hours I have measured a power loss of just 0.01v. This compares with about 0.12v with the Lowpowerlab library.
OK I spoke too soon. I’m getting a similar power loss over a longer period so no real difference. I can’t figure out why. Im leaking current somewhere and it has something to do with either the sensor or the radio. I only have a basic multimeter so can’t do any real current over time tests. I need a storage oscilloscope for that but can’t afford one. If I run the chip on its own then the current drops down to micro-amps in sleep mode. When they are connected it is 7mA. It’s really weird and I spent hours yesterday trying to figure it out to no avail. More investigations are needed.