Voltage divider for FrSky
Very simple voltage divider for FrSky.
I use 3S battery, so I have maximum 12.6V while FrSky accepts only maximum 3.3V on its analog inputs.
This time without schematic because there is no need to draw two resistors and two connectors:-)
For my case 1/4 voltage divider is just enought. I made it from 1.5k and 4.7k resistors, so with 12.6V on input it will give about 3.05V which is fine for FrSky. I made is as small plug, so I could make connecting cable of any lenght and change it in future without resoldering of divider.
Pictures, pictures 🙂
Voltage divider inside
Voltage divider – ready
Just works 🙂
just to be clear: this divider isn’t designed to plug directly into FrSky receiver or battery plug! It will not work that way! It must be plugged to power harness similar to my power splitter and another plug should be used for connection with receiver.
Hi Marek, ive stumbled upon youre website looking for info on frsky telemetry. I have been struggling to understand fully how to set up voltage telemetry. Your site has helped me understand i need to make a divider to take my 3s lipo down to lower than 3.3v to go to the rx input. Im using a d4r-II. Ive heard people mention not to send a ground from the divider to the rx so to avoid ground loops, do you know if this is the case? Sorry to be so uninformed but electronics is really not my strong subject. As i understand the + and – of the 12.6v lipo are connected to one side and 3.3v + and – from the other side are connected to the rx input.
Thanks Alex
Hello Alex,
people talking about ground loops have right. It’s general design rule that there should be only one common ground point in each circuit, and this case is no exception 🙂
Observe that ground is already connected from battery via esc/bec, so redundant path could result in unnecessary current flow via receiver (which is bad).
So, safe connection could be:
battery (+) is connected to 4.7k resistor, second leg of 4.7k is connected with 1.5k resistor and analog input of receiver (A1 or A2), second leg of 1.5k resistor is connected to ground (near battery or near rx – that’s almost the same).
Direct ground connection could be necessary for measuring second separate battery (for example for powering FPV equipment), but if OSD is in use, then battery grounds could be also already connected:-)
So, everytime we should be careful about connecting grounds 😉
I think that I should extend this post/article with simple schematic and more photos, as many people hits this page from google looking for ‘frsky voltage divider’ 🙂