RFM95W as alternative to RTL-SDR for Davis Vantage Pro 2

[John]

I have recently picked up a couple inexpensive  ESP32 / LoRa dev boards with an integrated RFM95W rf module in the 902-928 MHz range. I haven't delved into the radio capabilities outside of the LoRa modes but perusing the specs it seems like these might be a candidate for talking to the Davis Vantage Pro 2 ISS. 

A search for RFM95W in the forum was empty.  Has anyone else evaluated these i2c modules as a way to read the ISS directly with a raspberry pi ?

The ESP32 core on these dev boards has integrated Wifi and Bluetooth radios, making them a candidate for bridging the ISS directly to the lan and wan, or even to a distant LoRaWAN gateway using the RFM95W module.

https://www.digikey.com/en/datasheets/rf-solutions/rf-solutions-rfm95_96_97_98w

[rich T]

John

Right now they are using a RFM69 (don't know if they interfacing with a RPI) to interface with the Davis Vantage Pro 2 ISS, so I don't see why you can not use a RFM95W.  Did you try searching WXforums? Right now I'm receiving data from my Davis Vantage Pro 2 ISS without any issues using a SDR, but I can see many possibilities where the RFM95W can be useful. And possibilities where both the RFM95W and SDR can be used together with weewx.

Rich

[kobuki]

The radio should be capable on paper, but the RFM9x series is only used for LoRa in the wild. The main problem is that there's no suitable driver for these modules for FSK mode. The RFM69 is cheaper for FSK and there are several FSK/OOK libs to choose from, plus it already has several working implementations for the Davis radio protocol. There's nothing keeping you from writing an implementation and a driver, but I'm not sure it's worth the effort.

[John]

Thanks for the pointer to the RFM69 discussions.

Now I am thinking of a change in strategy and just putting one of the ESP32+RFM95W dev boards into the ISS and send the data out directly, alternating between moderate range LoRa <-> LoRa peers and occasionally to a distant LoRaWAN gateway.  The ESP32/LoRa module looks to have a very low power mode (ULP) suitable for battery / solar operation. I have an dead ISS that I thought was only good for parts that I may be able to bring back to life with a new cpu/radio and deploy to the ranch cabin. 

https://github.com/LilyGO/TTGO-LORA32-V2.0

[kobuki]

That's an interesting idea. You might be able to use the console connector present on every SIM board to capture the same packets that are sent out on radio - if it's only the original radio that's dead. The only issue is the power consumption of the ESP32. Whatever ULP mode it has, WiFi will always consume orders of magnitude higher than an RFM module.

[John]

I'm kinda assumed the whole ISS board was dead but I didn't really dive into it at the time. I was thinking along the lines of just hooking up each of the sensors to the esp32 and use the ULP to aggressively sleep the wifi/bt between LoRa transmissions.  The modules I have came with a SD card connector so maybe log everything to SD and occasionally wake up the WiFi via a LoRa command for a drive by download.

[kobuki]

That's also doable, but a LOT of work. Plus the T/H sensor has a proprietary protocol, so you might need to replace that sensor. Then you still need to write handlers for rain, wind, solar/UV sensors (if installed) as they're not interfaced digitally, and light sensors are analog, require a special pulsing of voltage for operation, etc. If you do it and open source it, that might be useful for others. But then again, a SIM board is $128 if you live in the US...

[John]

Maybe hook up to the console connector then.  That would upgrade both my active station and perhaps salvage the old one as well. Does the console connector provide a buffer for the data stream so that I could just have the ULP wake up the ESP32, read out the data buffer, write to the SD, transmit, and go back to sleep?

[kobuki]

That might provide a working solution, if the console port indeed dumps the data packets (I remembered it does, but right now I'm not entirely sure). If it does, it should RS422 signaling. I'm not sure if it can be used to wake up your module without losing the first few data bytes of the 10 for a packet, but if it has uA power modes where it can listen on a serial port, it might be a viable approach. The data packets are identical to the ones used by the radio protocol, and there are interpreters for that in several languages, including C++ for Arduino, python, etc. Maybe the simplest is to relay the packets to the remote station and let it process them.

[kobuki]

I need to correct myself. The cabled serial output should be available on the RJ11 connector if an ADM3483 TTL-RS422 converter chip is installed on the wireless ISS. See this thread on wxforum: http://www.wxforum.net/index.php?topic=18656 (see also: http://www.wxforum.net/index.php?topic=28530.0)

However, you only need the 3.3V serial output from the MCU on the board (no need for the converter chip), which is apparently routed to pin 4 of the converter chip pads for easy soldered access. So you can just get normal TTL serial data out of there and forward it to your decoding appliance/code/weewx driver/whatever remotely. This approach is also interesting when trying to use a SIM board not made for a certain region. A smart little hack and we have a wifi/lora transmitter... OK, there are a few assumptions since I've never tried this, and the OP in the above forum thread never left feedback on success or failure. But I think it's worth a try.