I’ve been having great success with the uBlox NEO-M9N units on some robots here on the east coast. Your boards and the libraries make it really easy to interface over I2C. I’m now in the planning stages to shift over to the ZED-F9P units to craft some semiautonomous units. Should be fun. Base station and multiple rovers. My issue is radio experience. I have lots with packet radios and secure message transmission in noisy environments, etc. But I have no experience with telemetry radios. I assume they just take in a bit stream and send it out as is. My NRF and RHM units need commands and have buffer limits that the RTCM messages will overflow. Net net, they aren’t usable without another microcontroller doing the buffering work. Too much complexity. So I need some help.
I bought a pair of Holybro 433mhz units to play around with, and they’re fine, but paired only. Doesn’t appear they will handle one to many multicasting. Based on what I’ve read though it appears they will take in the RTK data and send it over to the receiving unit quite nicely as long as I get the baud rate right. Am I correct?
What recommendations does anyone have on a radio setup that will multicast?
The ESP32 series supports a protocol called ESP-NOW which is pretty cool, and support multiport over the 2.4GHz frequency. We implement it on the RTK Product line (so you can peak at our code but it’s a big code base: https://github.com/sparkfun/SparkFun_RT … ESPNOW.ino)
Connect to a caster - Your base needs one connection to the caster (WiFi, cellular hot spot, etc), then multiple rovers can connect to the caster. No need for radio multi-cast.
Thanks. The environment I’m operating in limits what I can do with Wi-Fi connections. And cellular is spotty. I’m familiar with the ESP32 and have several home IOT systems in place with them. But they are overhead heavy and other than acting as a radio transmitter/receiver I have no need for their CPU capacity in the robots.
I will check out the LoRa Serial product. Always happy to buy the Sparkfun hardware. I’m thinking I could also use a medium or long range XBee unit. These have been off my radar for years now, but they can send a serial stream and have 500m+ range. They don’t make 433 mhz units anymore so I’d have to use the 2.4ghz units or change out my current 915mhz systems. Has anyone tried the XBee with the RTK stream?
My review of your suggested Lora setup came up positive. I’ll take your word that 480 chars/sec over the air will handle the RTK stream from the uBlox units. That’s one of the datapoints I have been unable to confirm… just how much data/sec is transmitted to make RTK solutions work. I see the library code is up to date and handles base stations or rovers. All looks good. 915mhz it is. Swapping out the RFM69HW’s is easy. One line of code to change.
Oh, one question… how much amperage does one of the Lora units pull. Need to spec a battery pack.
As background, I had good success with the RFD900x telemetry radios from RFDesign with my SparkFun RTK units. They have a similar power output rating (1w) as the SparkFun LoRaSerial radios. However I frequently work at the limits of the radio range, and the LED indicators on the RFD900x units are hard to see and don’t give a lot of information. And I had to purchase enclosures from a third party.
I’ve purchased a pair of the SparkFun LoRaSerial radios as they come with an enclosure and there are more LED indicators to provide more info on the status of the radio link. I plan to test them next weekend.
The RFD900x radios claimed to support mesh and repeating modes, but I could not get a repeater to work reliably. The ability to put a repeater radio on a hilltop between my base and my rover would be a game changer for me. Land surveyors sometimes use repeaters to extend their RTK radio links in hilly terrain.