I am currently working on a rotor telemetry project. I plan to use an Arduino Portenta H7 mounted on the rotating part of the system to acquire data from:
9 × PT100 temperature sensors,
shunt resistor measurements (WSBS8518) read through an AMC1301 Precision ±250 mV Input Reinforced Isolated Amplifier,
DC current measurements using a Hall-effect sensor.
Since the measured data must be transmitted from the rotating part to a stationary part, my intention is to use Wi-Fi communication.
I would like to know whether it is feasible to connect three antennas to the Arduino located on the rotor, positioned 120 degrees apart around the circumference, all transmitting the same data simultaneously. The goal is for a second Arduino located on the stator to receive the signal reliably regardless of the rotor's angular position.
Do you have any recommendations regarding the feasibility of this approach, potential implementation methods, or alternative wireless solutions that would provide robust communication between the rotating and stationary parts of the system?
The antenna is mounted on the rotor, and at certain angular positions the rotor shaft may obstruct the line of sight between the transmitter and receiver.
What is the distance?
How much is the peak throughput? bytes per second raw data?
100% reliability does not exist, even over wires, so you need a protocol that is able to resend data.
Then you can probably use a dual diversity receiver like they use for drone telemetry. So rather than the transmitter having multiple antennas the receiver has two antennas.
I have no experience with diversity receivers. Could you explain how they work and where they would be located in this application? Would the diversity receiver be installed on the stator with three antennas, while the rotor still uses a single transmitter antenna?
Are there any reference designs or projects that use this approach for telemetry?
I'm also trying to understand whether a diversity receiver is a complete RF receiver system, or if it acts like an antenna extender/switch that would allow multiple antennas to be connected to my Arduino transmitter.
The receiver is on the stationary part. It has two antennas that you can place at different locations, so at least one or both antennas will pick up the transmitted signal.
I've never used one so not sure how it combines the two signals but it probably uses signal strength and or bit error rate to decide.
Another alternative might be a 433 MHz /860 MHz transceivers. These are typical used in remotes, weather stations, lora etc.
Think of them as wireless serial, easy to use.
Protocol wise, send packets like this
{ Start, seq nr, valueId, value, value, crc}
The receiver can check (crc) for packet integrity, missing packets (seqnr). Typical a packet is responded by an { Ack, seq nr} or { nack, reason}
Regarding the software side of your project, do you already have a particular software stack or library in mind for implementing the Wi-Fi communication between the two Arduino boards?
I agree with your thinking. That was my assumption as well, and I had planned for only that antenna to be used in the RF setup. Given the constraints, I don't see a reliable alternative solution either.
I was considering the 868 MHz SRD sub-band. The architecture would look something like this: MEASUREMENT ON ROTOR -> PORTENTA H7 -> 868 MHz TRANSCEIVER -> 3-WAY RF SWITCH -> (A1 A2 A3).
Though I understand that your priority right now is the hardware side, as an idea for when you get to the software stage, you can use the Mongoose Networking Library on the Portenta H7 for network communication.
Mongoose already handles the Wi-Fi/networking part, with a simple-to-use API, so you can focus mostly on your application logic and on sending the acquired data.
We have a minimal Portenta H7 example here:
This can serve as a starting point once you move on to the software implementation.
Heads up: I am part of the Mongoose development team. I hope this will help you in the future.
Certainly possible, but only if you can build the matching network to split the RF power, equally, three ways. Each single antenna likely has a 50 Ohm impedance. Your network must match those in parallel to the 50 Ohm feed point.
