Radio-based Telemetry Receiver PCB

The goal of this project was a one way telemetry system for Formula Student car.

Design requirements:

• Minimal range – 100m in open field. This could’ve been achieved without LNA amplifiers, but for extra reliability, it was chosen to use them.
• Transmit power: +20dBm – maximum power allowed in Europe.
• Omnidirectional antenna, with 2dBi gain.
• Transmitter placed in front of the car with other electronic components, on standardized motherboard.
• Acquired data would be transmitted to the computer, where it would be stored and analyzed.
• Transmitter and receiver would be powered with 5V (Voltage provided by the motherboard(https://www.instructables.com/Multi-PCB-Motherboard/) for the transmitter, and by the USB port for the receiver).
• The car is made out of carbon fiber composite, with aluminum honeycomb between the carbon fiber sheets. Honeycomb and carbon fiber are electrical conductors, so the antenna needs to be mounted outside the monocoque
• The car uses 1Mbps CAN bus, so the telemetry system should be able to transmit data with speed >1Mbps.

Transmitted data:

• Accelerator pedal position o Brake systems pressures
• Speeds of all 4 wheels o GPS position
• Power, that the inverter sends to the motor
• State of charge of the low voltage battery.
• State of charge of the high voltage battery.
• Inverter temperature
• Motor temperature
• Low voltage battery temperature
• High voltage battery temperature
• Water temperature
• State of the car
• Tire temperatures

Whole project can be found here: https://github.com/PUT-Motorsport

Project supported by: jlcpcb.com/HAR

Diagram of the whole receiver-transmitter system looks like this.

Transmitter is based on STM32 microcontroller and NRF24L01 Radio IC. Transmitter is also able to log the incoming data to SD card.

Transmitter is based on STM32 microcontroller and NRF24L01 Radio IC. It is offering PC connectivity by USB C connector.

Silicon Labs calculator has been used.

4 layer PCB was used, cause of lower distances between copper layers, and simultaneously not significantly higher cost. The ground plane was poured on every layer. The 3.3V power was routed on layer 2. JLC PCB JLC04161H-7628 stackup was used:

Final layout was designed to fit on the top of already in-use motherboard: https://www.instructables.com/Multi-PCB-Motherboard/

Now that we’ve got the PCB design, it’s time to order. For that, you just have to go to jlcpcb.com, and click on the “Instant Quote” button.

You don’t have to worry about the settings here, because you can adjust everything in the new appeared tab. JLCPCB is also a sponsor of this whole project (not only this PCB, but all the PCBs in the car!). JLCPCB (Shenzhen JLC Electronics Co., Ltd.), is the largest PCB prototype enterprise in China and a high-tech manufacturer specializing in quick PCB prototype and small-batch PCB production. You can order a minimum of 5 PCBs for just $2 (2 layers), just enough to have a few test/spare ones.

To get the PCB manufactured, upload zipped Gerber files as you can see below. How to get them in KiCad 5? JLCPCB made the whole tutorial right here.

After uploading a zip file, you’ll see the top and bottom of your PCB as example shows.

After making sure your PCB looks good – by clicking Gerber viewer, you can now place the order at a reasonable price. In case of this project, there is 8$ for 5, 4-layers PCB and it’s only 6-7 days build time(the time is extended due to the chosen color). To place the order, click on the “SAVE TO CART” button. Fast and cheap, right? 

The quality is always really satisfying so we sincerely recommend JLCPCB.

The PCB’s were manufactured by JLC PCB. Their services are fast and affordable. The 4 layers PCBs are impossible to do at home, especially with so small spacing between tracks, large amount of vias and the high precision required by the RF signals routing. We’ve chosen to solder the PCBs ourselfs, but JLC PCB also offers soldering services with huge selection of available components.