tinyFISH FC — betaflight current sensor calibration

By | January 18, 2017

This post will show you how to calibrate the on-board current sensor on any betaflight based FC. I will do this based on the tinyFISH FC, your FC will probably need some different values. This tutorial is based on betaflight 3.1 and beteflight configurator 1.8.9.

Tools needed:

  • a flight controller of your choice with built-in current sensor
  • a lab power supply
  • a high current sink (see below)

First of all we need to find an appropriate current sink. You can use two parallel 50W halogen light bulbs for your FC running on 3-4S Lipo batteries. For the tinyFISH FC or other small 1S flight controllers you will need something different. I used five meters of 22 AWG wire, this draws around 9A at 4.0V — perfect for calibration. The wire will get warm over time so only connect it for short periods!

The best time to do this calibration is before you assemble your quad. Take your flight controller and power it with your lab supply. Set the voltage to the correct value and connect it to your FC (we use 4.0V on the tinyFISH FC, bigger FCs can use 12V). Make sure to use an appropriate wire thickness.

Fire up the betaflight gui and enter the “Configuration” tab. Scroll down to “Current Sensor”. Now briefly connect your load to the V output tabs and have a look at the screen:

Notice the current “Scale” value of 1360. You can read the calculated current value in the “Battery Current” textbox. Now check the reading on your lab supply, in my example it shows 11.3A — the calculated value is way off! In my case (bigger value shown) we will have to increase the scale value. Note: If you change the value you will have to click “Save and Reboot” before the value has an effect. I adjusted it to 2300 until i got a good match:

For the different tinyFISH boards i calibrated i needed values between 1900 and 2500 — i never though those resistors would be off that much.

Now remove the current sink and have a look at the calculated battery current. In most cases it will match the current shown on your lab supply. If there is an offset, you will have to do a real 2-point calibration. I will write a tutorial on that in the future, for now the simple 1-point calibration should be enough.

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