Hi guys,
Correct, you need Serial.flush() before every entering into sleep mode, made me mad until I found it.
Concerning coin cell, I've made several node using them, then send data to emoncms with my dual gateway board (RFM12B + RFM69) and I'm facing the Coin Internal resistor problem.
I was hoping sending data until battery come to 2.2V (min voltage for RFM12) or 1.8V (for RFM69) but on the real life, all my nodes start loosing send packet from about 2.7V of the battery. I spend much time to figure out until I read this excellent document from TI
http://www.ti.com/lit/wp/swra349/swra349.pdfVery good reading, this mean at 2.7V peak current can be up to 12mA for RFM12B and so decrease voltage for about 0.5V, and we're at the limit of RFM12B, and it's same thing with RFM69 (more current about 30mA) even it it works until 1.8V the voltage drop is about 1V.
Of course I tried adding 100uF cap in // of the battery to see (suggested in the doc above)
I will try with RF module in sleep mode instead powering it off with mosfet, may be startup will need less peak current like this and will work longer.
Anyway this is not the ideal solution, so I need to go backward to my 1st idea, add Boost Converter and enable it only when I need juice, this is working fine also but I need to do another design.