Transmitter digital pots??

S

steamer

Guest
--Have googled all over the place, but can't find an explanation
for this. I'm trying to take a "standard" Futaba FM R/C transmitter and
replace a knob-controlled third channel with an on-off or momentary-on
switch. Trouble is the knob isn't connected to an analog pot, but instead
somehow puts out a varying (depnding on position) pulse train (am I
expressing this right?). So how does one interface with the circuitry and
with what to add a switch which, in one position puts out one pulse train
but in the other position puts out a different one?
--Any help or links appreciated,

--
"Steamboat Ed" Haas : What if the whole world
Hacking the Trailing Edge! : farted at the same time?
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---
 
steamer wrote:

--Have googled all over the place, but can't find an explanation
for this. I'm trying to take a "standard" Futaba FM R/C transmitter and
replace a knob-controlled third channel with an on-off or momentary-on
switch. Trouble is the knob isn't connected to an analog pot, but instead
somehow puts out a varying (depnding on position) pulse train (am I
expressing this right?). So how does one interface with the circuitry and
with what to add a switch which, in one position puts out one pulse train
but in the other position puts out a different one?
--Any help or links appreciated,

The transmitters use pulse-width modulation. I don't remember the
Click to expand...
exact numbers, but for each channel, there's a steady pulse train,
and when you move the control one way, it increases the pulse
width, and when you move it the other, the pulse gets narrower.

So you'd have to look up or measure those pulses, and to duplicate
it, make a pulse generator with controllable pulse width. This is
called Pulse Width Modulation, PWM.

Good Luck!
Rich
 
Rich posted:
<< steamer wrote:

--Have googled all over the place, but can't find an explanation
for this. I'm trying to take a "standard" Futaba FM R/C transmitter and
replace a knob-controlled third channel with an on-off or momentary-on
switch. Trouble is the knob isn't connected to an analog pot, but instead
somehow puts out a varying (depnding on position) pulse train (am I
expressing this right?). So how does one interface with the circuitry and
with what to add a switch which, in one position puts out one pulse train
but in the other position puts out a different one?
--Any help or links appreciated,

The transmitters use pulse-width modulation. I don't remember the
Click to expand...
exact numbers, but for each channel, there's a steady pulse train,
and when you move the control one way, it increases the pulse
width, and when you move it the other, the pulse gets narrower.

So you'd have to look up or measure those pulses, and to duplicate
it, make a pulse generator with controllable pulse width. This is
called Pulse Width Modulation, PWM.
You guys may be more up-to-date on Futaba than I am, but I believe the control
knobs and switches simply vary resistance just as in the "old" days. The
conversion to PWM is done on the transmitter's circuit board. I have a 6 month
old systen (non-Futaba) that is as I describe.

The conversion should be as simple as removing the wires from the pot and
connecting them to the switch and resistor(s). To help any further, we would
need to know if the pot has two, or three wires on it, and what is the
resistance of the pot at the end of the control knob movement at each end.

Don
 
Dbowey <dbowey@aol.com> wrote:
: You guys may be more up-to-date on Futaba than I am, but I believe the control
: knobs and switches simply vary resistance just as in the "old" days. The
: conversion to PWM is done on the transmitter's circuit board. I have a 6 month
: old systen (non-Futaba) that is as I describe.

--Been there, not the case. We put a voltmeter on my xmitter last
night and there was n variation detectable in what was being put out by
the pot, regardless of position. Hopefully someone will bring an
oscilloscope to the next class and we can sort it out a bit further.
--At this stage plan B is to talk to a pal who works at Parallax,
as I've heard there may be a Basic Stamp hack that will solve the problem.

--
"Steamboat Ed" Haas : If you tune a crow
Hacking the Trailing Edge! : do you get a duck?
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---
 
--Update: a friend arrived at class last night and he brought his
oscilloscope and a voltmeter with an audible continuity tester. Turns out
when he used this and rotated the "pot" on the transmitter he got a series
of beeps. The "pot" is, in fact, a rotary switch that sends a series of
on/off signals to one or another location on the circuit, depending on
which way it's rotated. He says this can be duplicated via PIC chip and a
simple circuit in a day or so. Anyway he hopes to have a working
switch-activated remote weapon activator that we can plug into the
transmitter by class time next Monday. Woohoo!

--
"Steamboat Ed" Haas : If you tune a crow
Hacking the Trailing Edge! : do you get a duck?
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---
 
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