• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Question - Can I change a switch on my transmitter with a pot?

colorex

Rotor Riot!
Mentor
#1
Can I change an on/off switch on my transmitter with a pot and expect it to give me gradual changes in the signal?

My radio is an old 72MHz JR XP652 - and I don't know enough of the internals of the radio to know if it can be easily done. I assume the switches or pots just regulate the PPM signal directly - in which case it should be a question of just replacing the switch - but if the radio knows that this channel should be a switch it might only allow on and off values.

If this can be done, what resistance value should be used for the pot?

Final objective: Use the pot for smooth flaperons, and eventually an FPV pan servo.
 
#2
Good question, I think that a radio transmitter should recognize the pot as for the resistance, check off circuit with a pot currently on your remote. Just make sure to unsolder the pot before checking the resistance to avoid the board reading.

And also make sure to use a linear pot, not a radio pot since the output might be weird...
 
Last edited:

colorex

Rotor Riot!
Mentor
#3
Good question, I think that a radio transmitter should recognize the pot as for the resistance, check off circuit with a pot currently on your remote. Just make sure to unsolder the pot before checking the resistance to avoid the board reading.

And also make sure to use a linear pot, not a radio pot since the output might be weird...
Problem is I only have 4ch control + 2 switches = 6ch total, and no pots.

What is a radio pot?
 

colorex

Rotor Riot!
Mentor
#5
logarithmic character (as the ear) - not linear.
Oh, exponential increase. I see. That would probably only make it a bit harder to use, it would have more speed on one side than on the other.

So:

- Pot must be linear.
- As for the resistance, I didn't think right before, of course I can measure the pots on my transmitter! Each stick has two pots!

I'll check it out tomorrow.
 

colorex

Rotor Riot!
Mentor
#7
A radio pot can also be erratic or contain static, which will result in peaks in the output.
Which will obviously be transferred directly through the PPM signal - which I don't want.

I have a digital multimeter, but I'm not sure how to measure the resistance across the pots - I have settings for 2000k ohm - 200k ohm - 20k ohm - 2k ohm - and 200 ohm readings. I guess I have to measure across the whole pot to find the maximum resistance?

Does the circuit need to be powered up to measure?
 
#8
Hi,

The circuit must nog be powered up to measure the resistance, and to find the resistance of a pot you must measure across the whole pot. (little tip, most pots have their value written on them).

I dont know if it will work with your radio, on the 9X the switches are read as a digital input(if I'm correct), so connecting a pot wouldn't get you a analog reading.

KoekieMonster.
 
#10
If you measure in-circuit there is a chance that you'll end up measuring the board's resistance instead of the pot.

A resistance should normally be read off-circuit... That means un-soldering the pot to measure.
 

pgerts

Old age member
Mentor
#11
The resistance is not critical.
You are using the pot as a voltage divider and there is normally very little current going through the resistor.
But some switches are on digital inputs and can not be changed to analog signals. Dont know about JR 652 but im sure the information is on the net somewhere.
 

colorex

Rotor Riot!
Mentor
#12
I did some extensive Googleing, and I found this on RCGroups:

"No, it will not work. The XP652's gear switch connects to a Digital I/O pin on the microcontroller (M38223 pin 43). It is not capable of analog operation.

RC-CAM"

So that's kind of sad... I guess for FPV I'll just hook the camera up with the rudder channel.