Power budget
The dAISy has arrived. A quick comparison with the RTL-SDR and the RF sensitivity is about the same. (geography is my main limiting factor)I am powering the dAISy via 3.3v header on the PCB rather than USB, and receiving AIS sentences via the hardware TX pin. The dAISy utility seems to ignore me setting the onboard serial data rate to 9600baud, and continues to spit out at 38400, but the Teensy can handle this fine.
The remote unit periodically spits out its voltage over the LoRa link, whereby the Raspberry Pi logs this to the cloud to see battery performance over time
I am logging the voltage of the battery to thingspeak, which are plotted below. Values below are raw ADC values (12 bit input. 4.2V battery voltage scaled to 1.2V to match the Teensy 3.1 internal Vref ), and averaged over the last 10 readings
.
Readings are currently send from the remote device every 20 seconds, but at present the Raspberry Pi receiver crashes about once a day when a corrupt packet is received.
I am uploading to marinetraffic.com which gives some (delayed)
statistics on AIS message rate to give me some idea of the number of AIS
sentences I am likely to transmit
Current draw from the battery is 90mA @ 4.1v (0.37Watts) idle, rising to about 120mA (0.5W) on LoRa transmit, but not measured very precisely. Most of this is the dAISy
When the battery voltage drops below about 3.6V, I have the Teensy turn off the dAISy receiver and put the HopeRF into sleep, before itself sleeping for 20 seconds.
Every 20 seconds it wakes to measure the battery voltage, then sleeps again if needed.
Sleeping current is around 200uA, which can be improved with some effort
, but should not be significant
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