Mini Quad FPV Audio Mic Preamp

I currently fly FPV using a 7″ screen with a built in 5.8 GHz receiver. ie; no goggles here yet.

This screen has built in speakers, and I was curious if being able to listen to real-time audio would be helpful, or not.

The VTX has a mono audio channel and expects line level audio coming into it, so a simple single transistor microphone preamp circuit was chucked together on the breadboard so a small and inexpensive electret mic insert could be used:

_DSC4493_web

 
For a video feed on the bench, I just took a split of the STB composite out.

The first mic preamp was a fairly simple circuit, using a BC-547, as seen on the breadboard here:

_DSC4491_web

 
Levels are being monitored with the Behringer mixer, and the gain of this simple single-stage amp was inadequate.

_DSC4510_web

 
So an Op Amp based pre amp was put together on the breadboard, using this circuit:

_DSC4502_web

 
Although it has a slightly higher parts count, it has plenty of gain, and has a trimpot to adjust output level.

The TL061 has a specified maximum supply voltage of +- 18V. (ie: 36v), so it can run on 2S, 3S and 4S powered systems.

Here we see it feeding the VTX, and the ideal trimpot gain was approximately mid-way:

_DSC4498_web

 
Using a mixture of through-hole and SMD parts, what the finished preamp looks like on both sides of the Veroboard:

_DSC4506_web

 
Covered in heatshrink, and located facing rearwards in the aft of the Blackout Mini H Quad:

_DSC4514_web

 
Here is a video of the flight.

I got distracted with making sure the screen was in the video cameras frame… and you get to hear (and see!) the result of being distracted.

 
This project cost nothing, because all the parts were sitting there in the parts drawers, and was a bit of fun to do.
I estimate it would be around $10 of parts if you already had a small piece of Veroboard to begin with.

 
Is the audio useful?

 
Tool early to tell, but most FPV flying only uses 1 of the 5 human senses, so having some extra feedback on what motors are doing could be useful.

I can always turn the volume down anyway.

🙂