How to configure receiver's PWM output to NOT be a servo

[Farhad]

Hi. I just got a Taranis Tx with FrSky R8 Pro receiver. It has 8 PWM outputs. I'm flying a fixed wing airplane. I have everything configure and working. I have one special need, that is the output of CH 6 is a light, not a servo.

I want to configure CH 6 to output a constant HIGH or a LOW, but not pulse PWM between 1000us - 2000us. That is, the output is not a servo. It's a light. I want to manually turn this light on or off with a switch.

How do I define the output of this channel to a continuous high or low? (It is not connected to a servo)
thanks.

 

[Konrad]

Sounds like a job for a transistor.

Why would you have problem with a 22ms pulse?

The output of the RX (signal) is not to be used as a voltage source. Now it can be used to drive a transistor and the transistor would switch the Vss to turn on your light. As the RX is putting output a pulse you might want a resister capacitor (RC) circuit to bias the transistor.

Or better yet get a cheap amp from a $2 servo and use it to drive your light.

 

[Kilrah]

That's not how it works, you need an external RC switch that takes the PWM output and switches a transistor/relay based on the value.

 

[Haoyang Wang]

On internet, search for:
1. "pwm switch" or "rc switch"
2. "pwm relay" or "rc relay"
3. "rc engine ignition kill switch"
4. "brushed esc"
5. "rc led controller"

 

[Farhad]

Attached the PWM pin of the receiver to an oscilloscope and it showed the 1000us, 1500us, and 2000us when changing the 3 position switch. PWM is at 50Hz, 3.3V. I had thought I could have it always stay high and connect it to the base of a transistor then I would be done

If I don't program my own micro-controller to read how long the signal stays high, a PWM switch is $13 on Amazon (Canadian). Thanks for the clarification, I get it now.

 

[Farhad]

Sounds like a job for a transistor.

Why would you have problem with a 22ms pulse?

The output of the RX (signal) is not to be used as a voltage source. Now it can be used to drive a transistor and the transistor would switch the Vss to turn on your light. As the RX is putting output a pulse you might want a resister capacitor (RC) circuit to bias the transistor.

Or better yet get a cheap amp from a $2 servo and use it to drive your light.

I wonder if an RC circuit with an op-amp comparator is possible for controlling the transistor. t < 1300us, 1350 < t < 1700, t > 1750us. For me the most obvious and easiest way of doing it would be to program a microcontroller.

 

[HENNY]

The best way to achieve a switch type function is one of the servo / channel control switch. They are low cost and work perfectly. They can be purchase for under $10.