Build a FrSKY telemetry voltage sensor

by rcwingman | May 31, 2015 | (6) Posted in How To

A voltage sensor ....

measures the voltage in your RC vehicle.

This article is for RC-Guys with FrSky telemetry transmitters like Taranis, 9xr and a hacked Turnigy 9x radio who had already some soldering experience.
Its perfect if you do not have or cannot wait for a voltage sensor delivery for your FR-Sky system.

All needed parts can be purchased in electronic stores.
They are commonly salvageable from old electronic devices too.

In this tutorial I am going to show how to build your own FrSky telemetry voltage sensor from scratch.
I know they are cheap and can be had for under 3 bucks from HK. The parts you need will only cost you 50 cents and 15 minutes of your life time.

Here is a video i made for this tutorial.



It's really easy to do this. All you need is a resistor, potentiometer, soldering stuff and a FRSky receiver with telemetry like the D or X system.

You will basically need these tools:

  • a strong soldering iron
  • pliers
  • a screwdriver to calibrate the sensor or healthy long  fingernails.

I know the graphic above shows a 15K resistor and a 4,7k potentiometer and I'm talking about 20K and 5K in my Video... well..... It really doesn't matter. As long as you have a resistor ratio like 3:1, 4:1, 5:1. That simply means that the resistor has to be X-times greater than the potentiometer. Its called voltage divider. they are commonly used in electronics to measure voltages in devices. You can put a small capacitor on the positive and negative side next to your receiver to get a smoother reading but to keep it simple we just use to resistors. More about that later...

So you will need these materials:

  • 1x resistor with (lets say) 20k                                         => Price: 0,01$
  • 1x potentiometer (lets say 4 times smaller) 5k                 => Price: 0,10$
  • Some spare servo cables 1x                                           => Price: 0,20$
  • A PCB (optional) => you can solder the parts directly too  => Price: 0,20$


I you used a PCB for this. Now its a good idea to bring your stuff in place.

 Solder everything together....

Flux makes it easier for the wires. They will be stronger and more rigid too.
If you don't use flux they can become like a toilet brush and the strains can short out your electronics.

The yellow wire is positive and the brown one negative. In this example I used a D8R-II receiver.

Now connect your transmitter with 5V and the voltage sensor with a little bit larger power source and try to get a signal on your FRSKY voltage telemetry readings.

a simple adjustable, power supply makes it easy for the sensor calibration. It also shuts off automatically if the current goes over 1 amp. This "weakness" can save your RC electronics, life if you sort out your stuff. for the first try go for a voltage like 6 volts. That voltage will not blow your receiver up if you do something wrong. Except you reverse your polarity.

Now adjust the potentiometer until the value is right. Change the voltage to recheck the sensor readings.

If you cannot reach the right voltage just change the ratio in your telemetry menu of your radio. Go one step up or down and retry it.

Now you know how easy it is making a voltage sensor yourself.
You can make this real light. Even lighter than the ready made from hobbyking and safe some extra weight.

In conclusion i would always go for the own one, because you can build these sensors in no time with spare part.

Good luck and have fun.


Kurt0326 on September 18, 2015
Nice, very easy. Now can you build a individual cell voltage sensor? Bonus, how about for two 3 cell packs for a total of 6 cell? So I can monitor all 6 cells individually with out shorting it. I almost hurt my self trying this.
Log In to reply
rcwingman on September 30, 2015
as far as i know you need an extra microcontroller to do this. I dont think that you can solve this with a logic-circuit.
You have to do measurements with every cell on your lipo and connect each signal wire to an microcontroller analog-port. The microcontroller has to send the measure values to the FR-Sky telemetry receiver. This shouldnt be to complicated but it will take some days to write this code if there is no.
in the other hand I dont think there will be a huge benefit during flight except you are using batterys parallel to each other. measuring voltage is not a very accurate way to get the battery level. But its better than nothing.

Log In to reply
RedheadBarron on December 4, 2015
Why can't us spektrum folks use this technique? just curious.
Log In to reply
rcwingman on February 19, 2016
yeah this will work with every brand. Depending on the functinality of the receiver.
Log In to reply

You need to log-in to comment on articles.

Build a FrSKY telemetry voltage sensor