Using a HopeRF loRa board (not the Adafruit RFM9x breakout) with an Arduino pro-mini, the behavior I'm seeing is this: the LoRa sends one packet and the pro-mini resets almost immediately thereafter. I measured the current draw of the HopeRF board and right at Tx it spikes at ~470mA. That seems like it explains why the pro-mini resets since the power supply cannot provide any more. But, I'm wondering if anyone else has seen this behavior?
Background:
I'm working on a LoRa sensor node that will use an Arduino pro-mini (3.3v, 8 MHz), some sensors and a LoRa transceiver. I have the pro-mini and Adafruit RFM95w breakout board combination working. A Dragino LG-01-P is acting as the receiver and it gets data packets and sends an ack.
To lower cost and reduce power (by eliminating the voltage regulator - but really, it's mostly to reduce cost), I'm trying the HopeRF board. I soldered wire directly to the HopeRF board and have a prototype built on a breadboard. The same pro-mini runs the same code correctly with the Adafruit LoRa breakout. I've looked for differences between the HopeRF board and LoRa board on the Adafruit breakout but I don't see any - both ICs are marked RF96.
The circuit is as simple as possible. There are no discrete components in either case. For both the Adafruit and HopeRF, MOSI, MISO and SCK are connected to pins 11, 12 and 13 on the pro-mini. NSS/CS --> pin 5; Reset --> pin 6; DIO0/G0 --> pin 3. All power is 3.3v from a SparkFun FTDI board that provides that from the USB with a jumper.
Your output power is set to 23 dBm - the absolute maximum for RFM95 at PA_BOOST pin. The datasheet doesn't specify cupply current at that level, but it does specify 120 mA draw at 20 dBm (see SX1278 datasheet Table 6).
I would suggest lowering the output power to something more reasonable, like 10 dBm - depending on your location, 23 dBm output may not be strictly legal for ISM band.
jgromes:
Your output power is set to 23 dBm - the absolute maximum for RFM95 at PA_BOOST pin. The datasheet doesn't specify cupply current at that level
As the datesheet says the maximum power output of the device is 20dBm, its no surprise that it does not quote the current consumption for 23dBm.
jgromes:
Your output power is set to 23 dBm - the absolute maximum for RFM95 at PA_BOOST pin. The datasheet doesn't specify cupply current at that level, but it does specify 120 mA draw at 20 dBm (see SX1278 datasheet Table 6).
I would suggest lowering the output power to something more reasonable, like 10 dBm - depending on your location, 23 dBm output may not be strictly legal for ISM band.
Yes, a quick test showed that the pro-mini did not reset after dropping the LoRa /HopeRF Tx level to 10 dB. I need to make more measurements. But there's some progress.
Well, probably not very accurately! Um, I'm just using an old digital multimeter and measuring the draw of the HopeRF board in the simplest way. That is, the meter is in series with the board.
Do you have any suggestions for measuring the current as a function of time? I do have a simple oscilloscope. (this is probably something I should google...
jhrg:
Do you have any suggestions for measuring the current as a function of time? I do have a simple oscilloscope. (this is probably something I should google...
Google 'USB Power' meter.
One of those can be used to tell you the mahr used over time.
