Analog Voltage sensor for FrSky X8R Receivers

Quick Overview

The FrSKY X8R receiver is a great unit but it is lacking an easy external voltage sensor. This interface allows you to easily monitor an external voltage source like the motor battery for an electric powered aircraft.
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Please note that this is a neat little product brought about by FrSky users, and is not a FrSky manufactured product.

This device can be used to report voltages via telemetry with the X8R receiver and the FrSky Taranis transmitter. It utilizes a small 8 pin microprocessor to sense a voltage via an analog to digital converter and a voltage divider circuit. This board has its own 3v3 power supply and is fully self contained. There is a blue power indicating LED that will light when connected to the s.port interface on the X8R receiver.


Voltage Range:


0.0 - 18.2v (will support higher voltage, but will only report the ranges listed e.g. will report 18.2v until battery voltage drops below 18.2)
NOTE: DO NOT exceed 25v or you will damage the microprocessor.


Hi-Resolution jumper: Selects the resolution that the X8R2Analog uses to report voltage.

Jumper installed: Improves accuracy (useful for 3S and smaller batteries)
Jumper not installed: Normal accuracy
Note: Make sure you enter the correct MAX voltage in the Taranis telemetry setup so the scaling of the values are correct.

X8R Connection:

Use a standard servo extension cable to connect to the s.port connection on the X8R (not the s.bus connection). This device must be the only or last device in the s.port chain as it does not support pass through. Please verify the pinout prior to connection with specific interest on matching the positive and negative wires. Serial to S)ignal, positive to +, negative to -


Connect to the voltage source being monitored. Please maintain the correct polarity. One of the terminals is labeled Analog-In, this is where the + or positive terminal of the battery you are monitoring attaches. The other terminal is labeled GND, this is where the ground of the battery you are monitoring attaches... See the diagrams and notes below.
Note: if you are using the FBVS-01, you can connect that to the Ground and Voltage In connections. You will also need to remove the left most through hole resistor, the one closest to the microprocessor, and replace it with a jumper wire.


  • These do not provide pass-through of the s.port connections.
  • If you are using an FBVS-01 external voltage divider, you will need to remove and jumper the resistor highlighted above. Just clip it's leads and pull heat the pin and pull them out and replace it with a wire jumper. This resistor is a 15k 1/6watt resistor if you need to replace it in the future.

Installation Instructions:

  • Connect a servo extension cable between the s.port on the X8R and the s.port connector on the X8R2Analog board. Be sure and maintain the proper connections. Serial to S)ignal, positive to +, negative to -.
  • If you will be using this to monitor the voltage of a 3S or smaller LIPO battery, you may jumper the high resolution jumper to gain a little more accuracy in the voltage readings. Be sure you adhere to the Voltage Range warning if applicable. For 4S batteries up to the max voltage limit, you may leave this jumper off.
  • Connect the voltage source that is to be monitor to the Analog-in pin location. If you use multiple ESC's or BEC's and your X8R receiver shares a common ground with them, you do not need to connect the ground on the analog-in pins. Only connect the analog-in connection to the positive lead on your LIPO battery. If your X8R receiver is powered from a separate battery or does not share a single point ground with the LIPO battery being monitored, there is a 47 ohm resistor that should be installed in series with the ground of the battery you are monitoring. This will act as a fuse in case your primary ground fails and will protect your receiver and the X8R2Analog interface.

Common single point shared ground setup

RX with separate battery or no shared ground


Questions? Need some help? Please visit the creators blog on RC Groups at this link. (Click Here)

UPDATE: Having issue with your sensor not powering up with your new X8R? FrSky recently upgraded the firmware on the X8R, as a result, you will need to update the firmware on this sensor too. Please see this thread for further details: (Click Here)

UPDATE 4/16/2014: Sensors come with the upgraded firmware to work with current FrSky X series receivers. 

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Works as advertised. Review by David
Connected to the Smart Port of a FrSky X8R to monitor a 3s Lipo it worked perfectly out of the box. No re-flashing or other drama. (Posted on 5/17/14)
Good Product Review by DanFlys2Hi
How great is this voltage sensor! I have 2 of the older style and 2 of the newer one, and one of each has the High Resolution jumper on and they all work perfectly with 2S and 3S and without the jumper 4s works great. Works with common ground (analog in only) or wired with a separate common. Each way you wire it though (I.E. with or without jumper, and with or without common ground) all have different ranges on your A2 channel, but once range set, seems to work accurately up and down the voltage scale. Thanks. (Posted on 4/30/14)
Good product Review by Roland
Soldered pins, connected to s_port, connected battery source, and set up a2 in transmitter. Voila works like a charm. (Posted on 4/24/14)
Don't buy this unless you are ready and willing to reprogram it Review by John
First let me say , if and when you get it working , it's great! now for the bad.. if you have a newer X8R , this will not work until you reflash it.
to do this you will need to research , dig through countless pages in forums, buy more parts, and sharpen your soldering skills.

if you like to tinker and read forums till whee hours of the night , this product is for you.

if you expect it to work when you get it.. you will be disappointed.

I rated this product 1 star... not really for the product itself but for the overall experience it takes to get this working as intended (Posted on 3/28/14)
Battery voltage the easy way! Review by Dave
The device works perfectly and doesn't require fine tuning like the frsky divider!

It can be reprogrammed by you or many others to keep up with frsky changes and it now works with the x6r, too!

(Posted on 2/17/14)

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