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R/C Controlled Voltage Regulator for Video Transmitter

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A fellow asked me how he could create a R/C controlled voltage source for his 800mW FPV video transmitter (vTx). According to his supplier's information, the vTx's RF power could be varied by the operating voltage. He reasoned he could fly on lower power, and if the RF link became weak, he would flip a switch on his R/C Tx to increase the RF power (and turn around!). He wanted three RF power levels, Hi, Med, Low.

Creating a R/C controlled switch that supports three voltage (RF power) settings does not take much effort. As they say, there's an app for that. So let's do it!

Along with a standard 3-wire servo cable with bare leads, you'll need these two things (from my favorite supplier) :)

The triple camera switch was designed to switch video but it is perfect for this project. It will be connected to the voltage regulator (Vreg) with some resistors, but the required soldering is minimal. As you have probably realized by now, the resistor choices determine the Vreg's output voltage. Since the adjustable POT on the Vreg will be set to the highest required voltage, only two additional resistors are needed for the other two lower voltages.

In this case the Vreg's POT will be initially set to 12.0V. A 22K resistor will provide 10.5V and a 10K resistor will give 9.0V. These voltages choices are based on the published specs of the vTx being used and will give High (800mW), Medium (450mW), and Low (300mW) RF power. Other voltage combinations are possible by choosing different resistors (don't ask me what to use for your vTx, that part is up to you).

So here is how easy it is (these instructions are for a 12VDC vTx).

  1. Before any modifications, set the Vreg so that it provides 12VDC to the vTx.
  2. Solder the two resistors to a 3-wire servo cable, as seen in the photo: 10K (red wire) and 22K (white wire).
  3. Solder the black servo wire to the pad on the Vreg.
  4. Solder the two resistors to the two connected pads on the Vreg: 10K ( PCB pad A ) and 22k ( PCB pad B )
  5. Plug the servo cable into the R/C switch, EXACTLY as shown.
  6. Plug the R/C switch into your R/C receiver using a channel that is assigned on the R/C Tx as a 3-position switch.
  7. Be sure to test it out BEFORE connecting it to your vTx. Confirm the three voltages are what you need, otherwise try other resistor values.

That's it. Now you can flip the switch on the R/C Tx and control three RF power levels on the vTx.



Note: My photos still show bare wires and resistors that need better placement. This is just to show you how to wire it up. I'll leave the important construction details up to you. Also, I do NOT recommend that you sandwich the R/C switch against the Vreg since this might couple EMI/RFI into the R/C wiring. Instead, place the Vreg a few inches away from the other electronics in your FPV model.

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