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Needing a little help with wiring a VTX

graywoulf

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Hey guys! I'm just playing around with modding my Tinyhawk Freestyle and I need some advice on installing an upgrade VTX on it. It is a pretty much straightforward install as far as the power and video connections but this VTX, the HGLRC Forward VTX Mini, has wire labeled "RX" that I am not sure of it's purpose and my Tinyhawk FC has four connections that it's original VTX used which are the power, the video and a audio connection. Should I connect the Forward VTX "RC" wire to that connecting point? Here are the pinouts for both devices and thanks for any and all help on this.

HGLRC Forward VTX Mini Pinout.JPG Freestyle VTX Pinout.jpg
 
The RX pin is for "smart audio". I know there's a reason for that name, but it's still a stupid name for control by wire. You would connect that wire to a free UART and use it to control your VTX via software, but you don't need it. Without that wire you need to use the button on the VTX to change the channel and power settings.
 
Thanks for that information. Now all I have to do is figure out where that UART connection is on the FC. I have read that there is two UART's on the FC board and that UART 1 is not used and UART 2 is for Smart Audio. I'm still learning the labels and their meanings and now I know that the RX connection is for SA. Thanks again.
 
@graywoulf
The Audio connection/wire is not for audio, it is calling out smart audio, meaning it is the same connection as the one labeled RX on the HGLRC.

@rtkDarling
The Smart Audio conforms to a standard that actually can do both audio and the control signal together, you just need to put a small capacitor between the actual audio (microphone) and the UART/vTX.

Check out this TBS link and check the pictures.

 
The Smart Audio conforms to a standard that actually can do both audio and the control signal together, you just need to put a small capacitor between the actual audio (microphone) and the UART/vTX.
Ahh, so it's a genius idea, and a rather fitting name after all :)
 
Thanks for all of the information and education. So, tell me if I have this right. And do I need the extra ground wire for the video signal? And what kind of capacitor do I need for this?

VTX Wiring Diagram.jpg
 
That wiring is almost correct, but there are 2 things...

You do NOT have a microphone to give you sound, so you will not need a capacitor since you have no mic. You do not need to wire the GND/5v pair, they are for powering the FPV camera if the camera can run on 5v.

The biggest issue I see is that the old vTX ran on 5v, but the new vTX needs 7-26v, so you cannot run the new vTX off the old 5v wire and you will need to attach it to someplace with VCC or VBat, like directly to the battery pigtail. And you will need to run at least 2s batteries to give the vTX enough voltage to run. If there is a 9v or 12v pad somewhere on the FC, one of them should work also, but I don't know what is available on the THFS FC.
 
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It looks like his new vtx does have a mic on it. Upper right corner of the pic. Are you referring to the quad itself?
 
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It looks like his new vtx does have a mic on it. Upper right corner of the pic. Are you referring to the quad itself?
I didn't notice that, but it is on the vTX so it will not use the audio pin for actual audio. it will come straight from the vTX into the audio channel of the video stream automatically.
 
Won't run at all

Well, that is not a problem. I overlooked one major detail here. The original VTX operated on 5 volts and I should not have drawn the diagram to show the HGLRC VTX powered by the FC to begin with. I will be connecting the VTX power leads directly to the battery leads as the Tinyhawk Freestyle runs off of either two 1S batteries in series or one 2S battery. Voltage issue solved.

So, now that you know that the new VTX has a microphone on it, will I still need the capacitor and will the RX lead still connect to the Audio connection on the FC?
 
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I don't think you can add a cap because the microphone circuit is not external to the vTX, or sharing the Smart Audio circuit, it is built into the vTX and the audio should be automatically added to the video signal. I know how hard a go pro filters the sound to get something half way decent, I don't think you will like the audio you get from that thing, but maybe if you turn the volume on your goggles down you may find some use for it.

As far as "will the RX lead still connect to the Audio connection on the FC?", I think the answer is yes. The "audio" labeled pad on the FC must be a UART (port) TX pin since there is no way the FC has a pad that has anything to do with actual audio. Smart Audio can be put on the TX pin of any completely unused UART in the FC.
 
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There is a cap already attached to the battery connection on the FC. I hope that will help with the noise if I attach the VTX power leads at the same connection. I'll just have to wait and see if it does help.
 
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A cap will always help, the questions are, did you even need one to begin with, and will it be enough if you do need it. Many makes now come standard with them because they are often needed, and at the very least they help reduce voltage spikes to hopefully help make things last longer.
 
Thanks for that video link. I had found it earlier but I had forgotten about it until a few days ago. It is a very good video for the Tinyhawk Freestyle upgrades. Mine are basically done all except for mounting the VTX and putting it all back together again.
 
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