Chorus RF Laptimer – 4in1 PCB (english)

I would like to introduce you to my most current project. I am very conscious to keep this article short and concise, but will of course include all important information that is required in order to re-construct.

A short preliminary remark: how I came upon this project
I had been on the search for an affordable and most important, functioning, FPV-lap timer for my friends and me. This led my attention to the Chorus RF Laptimer. This project had been brought to life by Andrey Voroshkov (Minsk). Спасибо за проект 😉 !
Every pilot is able to build his or her own timer and combine these on the field, so that multiple pilots can be tracked. I, however, wanted to build a timer for 4 pilots, which does not require stacking or to be connected modularly.
The Tracker can be controlled via Chorus App or LiveTime FPV software over Bluetooth / WiFi. Alternatively, you can also make a wired connection.

Since PCB-Design is something completely new for me, I have been spending time nearly daily for the past weeks and months learning about PCB-Design.

Now on the my 4in1 Tracker. My goal was to build a tracker that is as small and cost-efficient as possible. I finalized V3.1 (the third PCB that I designed), produced it and would like share it with you.

Facebook Community for the Chorus RF Tracker



  • PCB for 4 Nodes (4 Pilots)
  • easy extendable via JST XH cable (8 Pilots)
  • 5V stepdown for Arduinos
  • adjustable stepdown for RX Modules (use 3.5V to keep temperature low)
  • 92 x 92mm mounting holes
  • XT60 PowerIn
  • 5V USB PowerIn (if you want to use a powerbank)
  • stacked hardware – can be changed in seconds
  • Buzzer Port to connect one Buzzer per Node

What is needed

ordering PCBs

you can order the PCB from china:

  1. Go to Fusion PCB
  2. Upload gerber file (
  3. verify order settings
  • Base Material: FR-4
  • No. of Layers: 2
  • PCB Dimensions: 100mm x 100mm
  • PCB Quantity: 10 (you will get 10 identical PCBs – thats the minimum quantity)
  • No. of Different Designs: 1
  • PCB Thickness: 1.6mm
  • PCB Color: Red
  • Surface Finish: HASL
  • Minimum Solder Mask Dam: 0.4mm
  • Copper Weight: 1oz
  • Minimum Drill Hole Size: 0.3mm
  • Trace Width / Spacing: 6/6 mil
  • Blind or Buried Vias: No
  • Plated Half-holes / Castellated Holes: No
  • Impedance Control: No
  1. add to cart
  2. pay the order! Done!
  3. share unused PCBs with the community! =)


Optional accessories

Flash Arduino software

In order to flash the Arduinos, you will need the Arduino IDE and an FTDI Adapter.
Note: Always flash every Arduino when disassembled. Download the current Arduino Software from the Github Project, unzip the Package and open the “.ino” File

Connect your Arduino Pro Mini to the FTDI Adapter and then to the computer.
The FTDI Adapter and Arduino will be connected via the identically labelled connectors. Simply press the FTDI Adapter into the pin holes of the Arduino and hold them together during the flashing

5V -> 5V

Now you must select the correct COM-Port, select Arduino “ATmega328(5V 16MHz)” as the processor, and “Arduino Pro or Pro Mini” as the board.
No flash the code! ?

The final step requires you to click “Sketch” -> “Upload”. The code will be compiled and written to the Arduino.


Since only asks 5 $ for 10 pcs 10 mm × 10 mm, my goal was to fit all components onto a 10×10 board. That was not so easy in the beginning, but once all parts were made to be plug-n-play, it all became possible.


DipTrace Files / Gerber Files

I designed the PCB using the freeware 500 Pin Version from Diptrace. I found that working with the software was very convenient and effective. Unfortunately, however, the library of components is limited to standard parts meaning that I had to create nearly each and every piece myself.

Here you can download the files you need


Most of the circuit design was of course carried over from the Chorus Project. It was, however, completely redrafted and refitted for my 4in1 board. For the redundant power supply and buzzer, for example, I used several diodes.

Configure the bluetooth module

The Bluetooth module needs to be set with a Baudrate of 115200. There are several online instructions for doing this.

A rough guide is:

  1. Connect the HC05 Module via the FTDI Adapter to the computer
  2. Open the Arduino IDE, select the COM Port and open the “Serial Monitor”
  3. Enter the following command in order to edit the Baudrate: “AT+BAUD8” (the module then answers “OK115200”)

Tipp: Set a PIN Code, so that other people cannot access your Lap Timer

Less than 4 nodes?

You can use less than 4 nodes. All you have to do, is to bridge TX/RX (see silkscreen) of the unused nodes. Always use at least „Node1“ because the voltage measurement is connected to this node.

5 V power via USB

If you want to power the unit via 5 V USB, please remove stepdown marked as „Arduino“ and bridge IN and OUT of it to pass the power from the USB to the Arduios.

How to track 8 pilots and more

If you plan to track more than 4 pilots at the same time, connect just connect two or more PCBs together.

  • Please ALWAYS set the „Loopback Jumper“ to the first PCB.
  • Connect all PCBs via 6Pin JST cable
  • On the first PCB, bridge MV
  • On following PCBs please bridge GM
  • WiFi/Bluetooth Module ALWAYS connects to the last PCB.


The App

I don’t want to bore you with a lot of words to the APP, because it is pretty self-explanatory.


The biggest problem to be overcome with the lap timer is currently the limited range of the Bluetooth. The HC-05 module is only able to reach about 15-20m, if you are lucky. For safety reasons, we sit a minimum of 30-50m away from our track. I am currently investigating possible solutions for the range issue.

Alternative Bluetooth Modul (Class 1)

I obtained the Bluetooth Mate Gold from SparkFun, which is what is being used by Team KA-NICKEL and has been claimed to have been tested to a range of about 60m.
The range is much better than with the HC-05 module.

Via Cable using RS232 Protocol

Markus Dicks uses the tracker with a lower Baudrate (9600). This way he is able to cover a distance of 30m using a network cable. This solution is perhaps the easiest and also work, but unfortunately, RS232 connections are not conceived for longer distances and there’s not a guarantee that it will work for everyone.

Via Cable using RS485 Protocol

A better cabled solution is able to be utilized using the RS485 protocol. I am currently working on a full duplex link, which can simultaneously power the Bluetooth module. Using this method, a range of 100m and more could be possible. A step-up regulator can, if needed, be installed. If not, the solder bridge circuit will simply be closed. The step-up is used to compensate any loss in voltage over longer distances and bring the current back up to 5V.


Using RF: 2.4 Ghz or 433 MHz

A second possibility can be achieved using a radio frequency. This allows a range of potentially 500m. However, I have not yet successfully been able to get the radio module functioning properly (Comms work, just not with Chorus and the Bluetooth module).

  1. Connect the 2.4GHz RS232 module with the FTDI (TX/RX RX/TX GND/GND VCC/VCC)
  2. After setting the current in the 2.4GHz RS232 module, connect the CMD Pin with GND
  3. Open a serial monitor on baudrate 9600
  4. Set the ID with the following command: “AT+ID=xxxx”
  5. Set the baudrate to 115200 with the following command: “AT+BAUD=7”

Wenn dir dieser Artikel gefallen hat und du mich unterstützen möchtest, findest du hier ein paar Möglichkeiten. DANKE!
If you liked this article and would like to support me, here are a few options. THANK YOU!

12 Responses

  1. Radek sagt:

    Any news on RS485 pcb?

  2. Romanas sagt:

    Any news when will you share to seeedstudio?

  3. HC-11 and HC-12 are other options range extending in 433mhz.

  4. Andreas Mettel sagt:

    Gibts schon neuigkeiten?

  1. 2. August 2017

    […] Chorus RF Laptimer with 8in1 PCB 27. Juli 2017 […]

  2. 11. Oktober 2018

    […] Nächster Beitrag Chorus RF Laptimer – 4in1 PCB (english) […]

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