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PICList Thread
'RC Transmitter'
1998\05\05@142130 by Andres j Ogayar

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Hi there!

   I'm working on a hobby R/C transmitter and receiver for controlling a
blimp. While there are some possibilities for both, I'll be using an
standard receiver/decoder (LM1872) because it is light and easy, but I'd
like using a PIC (16X84) for the transmitting logic.

   The idea is having 'something' (read a 555) reading a potentiometer
position and generating 1 to 2 ms pulses depending on its position -1,5 ms
will be on the center-.

   There will be four to six of these devices attached to PIC entries, and
one output will generate the full wave, combining all input channels and
the sync pulses.

   The question is: has anybody made some coding remotely similar to this
using PICs?

   If so, would you share your code?

   I know that doing myself things will enhance my overall knowledge, but
as I work as full time IT support for a big enterprise, this is just a
hobby, and I have very little time, so your help will be greatly
appreciated.

   Thanks in advance,

   Andres j. Ogayar

1998\05\05@185421 by Bill Cornutt

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----------
{Quote hidden}

Andres,

Scott Edwards http://www.seetron.com/ makes a Pic unit
that controls up to eight servos via serial data input.

---- End of useful Pic information -----

Andres,

If the last part of your post about having little time
was for my benefit, there is no need to worry about what
I may say.  I am just a big bag of wind.  I am not out to
change the world or anybody in it.  But when I see someone
who may need a little push to get on a better path, I will
tell them so.  I try not to embarrass them nor intimidate.
I also try to add some humor.  I do not do it to criticize.
When I go too far I am sure others will tell me about it.

Have fun with your blimp.

Bill C.   spam_OUTbillTakeThisOuTspamcornutt.com

1998\05\05@194620 by 'Grif' w. keith griffith

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At 19:15 5/5/98 +0200, you wrote:
>Hi there!
>
>    I'm working on a hobby R/C transmitter and receiver for controlling a
>blimp.
>    The idea is having 'something' (read a 555) reading a potentiometer
>position and generating 1 to 2 ms pulses depending on its position -1,5 ms
>will be on the center-.

Why not a/d the pots, and be able to do your channel mixing/trim stuff
digital instead of analoge?  The old Ace MicroPro 8000 used 8 bit a/d, the
new commercial rigs use 12 bits or something.  A hand full of the two
channel a/d 12 bit chips, serial out would give you all the data you
needed, and all the modifications you'll need to make could be done as
firmware/download instead of wire and solder.
>
>    There will be four to six of these devices attached to PIC entries, and
>one output will generate the full wave, combining all input channels and
>the sync pulses.

Might as well use 8 channels, that way, lazy folks would have the chance to
buy an off the shelf rx and servo set, and use all the channels from some
of the after market rx's. The new hitec am micro rx, batteries, and two
servos seems like it runs under 3 oz. FMA direct has several good rx's, am
and fm.  And you could spread your development over time and get a
functional unit in the air with out having the full tx/rx/servo designed
and built.  Not counting the commerical rx's are surface mount and really
light weight.  (yes, I know that's the same as cheating!!!)

>
>    The question is: has anybody made some coding remotely similar to this
>using PICs?

I think the Ace MicroPro was a 68x11 or one of those, several are still in
use around here, and have sold for about the same as a new modern tx if in
good shape.  I've lost a bunch of sleep thinking about the logic flow of
the design, but nothing on paper.  I'd be nice to do the remote mixture
control for carburated engines with an adjustable mixture curve, maby with
10 or 12 points,,, the list of fun stuff goes on and on.

Keep me posted,,, I'm really interested in following your project


>    Thanks in advance,
>
>    Andres j. Ogayar
>
>



'Grif' N7IVS

1998\05\06@180406 by Russ Steinbach

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A couple of years ago Circuit Cellar magazine had a nice article on using a
PIC to control model airplane servos.  I don't remember which issue.  Check
out there web site and see if you can get more info there.

Best regards,
Russ

{Quote hidden}

1998\05\06@201100 by paulb

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Andres j Ogayar wrote:

> The idea is having 'something' (read a 555) reading a potentiometer
> position and generating 1 to 2 ms pulses depending on its position
> -1,5 ms will be on the center-.

 Can I suggest you forget the 555s and simplify the thing completely?

 Just connect the joysticks (with a series resistor) to eight PIC
inputs with a parallel capacitor on each.  See the Stamp instructions
for plausible values.  Each capacitor is charged via an output "1" for
the two steps prior to measurement, then the pin is changed to an input
and times the next output pulse until it runs down past the logic "0"
threshold.

 A single-chip PIC implementation of a single-chip R/C encoder, using
the standard sequence.  Just what PICs are for!

 Cheers,
       Paul B.

1998\05\07@014729 by Mike Keitz

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On Thu, 7 May 1998 09:00:45 +1000 "Paul B. Webster VK2BZC"
<.....paulbKILLspamspam@spam@midcoast.com.au> writes:
>Andres j Ogayar wrote:
>
>> The idea is having 'something' (read a 555) reading a potentiometer
>> position and generating 1 to 2 ms pulses depending on its position
>> -1,5 ms will be on the center-.
>
>  Can I suggest you forget the 555s and simplify the thing completely?
>

Use one measuring circuit (such as a 555 or gate-logic RC timer) and
multiplex all the potentiometers into it with an analog switch IC or two.
If you use the pulses generated directly over the air, the digital logic
is extremely simple.  But you probably want to store the potentiometer
positions in RAM and do some calculations on them before sending to the
radio.

During the frame sync pulse, which is much longer than a servo pulse, the
transmitter software can measure all the controls since it doesn't have
to do anything with the output.  Using a PIC with a capture timer should
allow a 1 ms pulse to be timed to 12-bit precision.  This type of ADC
isn't good for general instrumentation use, but for this project it
doesn't matter if the end points drift around some.  You just want lots
of steps for smooth control and the possibility to scale, "mix" and
non-linearize the readings later.  After measuring is complete, the timer
would then operate in the compare mode to generate the output pulses.

I'd use a commercial hobby-type RC radio since it is much more powerful
than the LM1890-type stuff.  The National chips are intended for
short-range toy applications.  Using real RC radios it is generally
possible to control the model from as far away as you can see it.  Also
it is difficult to build radio equipment (that works well) from the
ground up.  But you can build your own encoder and/or decoder sections to
get the custom features you want, removing the radio section from a
bottom of the line 2-channel RC set.

Many 2-channel RC transmitters contain the Signetic chip (NE5040??) which
is actually a 7-channel encoder.  You just need to connect additional
pots to the unused pins.  Such a modified transmitter would still be
"dumb," so including a PIC for digital processing makes a lot of sense.

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1998\05\07@041135 by Andres j Ogayar

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-----Mensaje original-----
De: Mike Keitz <mkeitzspamKILLspamJUNO.COM>
Para: .....PICLISTKILLspamspam.....MITVMA.MIT.EDU <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Fecha: jueves 7 de mayo de 1998 7:47
Asunto: Re: RC Transmitter

>Many 2-channel RC transmitters contain the Signetic chip (NE5040??) which
>is actually a 7-channel encoder.  You just need to connect additional
>pots to the unused pins.  Such a modified transmitter would still be
>"dumb," so including a PIC for digital processing makes a lot of sense.
>
Mike,

   Thank you for the ideas! I realyy have to rethink on all of them, and
also have a look on the Signetics chip.

   The National chip will be used in a first prototype, since it has
everything included, but -on draft- there is a much more sophisticated
receiver with a double conversion, two intermediate frecuencies, etc, but
for a much larger design.

   The first blimp to be built will be -more or less- one meter length and
will lift only 300 grams, and will only be usable indoor.

   When something more solid than the ideas on paper will come, I'll
publish something to this list. Please think that i will be giving two to
four hours per Week! to this project.

   Thanks again,

    Andres.

1998\05\07@061729 by Zoltan Perhacs

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>>  Can I suggest you forget the 555s and simplify the thing completely?
>Use one measuring circuit (such as a 555 or gate-logic RC timer) and
I'm also want to build a R/C transmitter.
The hard part for me is the RF stage. Can someone help me in this (40MHz).
But, if you plan to use a PIC in your design why not use a PIC with A/D
converter ? Much sipmlier design and programming needed.

1998\05\07@083127 by Goeran Stigler

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Zoltan Perhacs wrote:

>The hard part for me is the RF stage. Can someone help me in this (40MHz).

Try buying a complete RF stage as a spare part. I had no problem buying one
when I thought my Hitec transmitter was broken.

Also, stay away from airplane frequencies unless you really know what
you're doing: a 2 kg plane doing 100 km/h can do _a lot_ of damage if
jammed out of control!

Cheers,


Goeran Stigler      <http://www.pe.chalmers.se/people/ghost/>

1998\05\07@092559 by Andres j Ogayar

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-----Mensaje original-----
De: Goeran Stigler <ghostspamspam_OUTPE.CHALMERS.SE>
Para: @spam@PICLISTKILLspamspamMITVMA.MIT.EDU <KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU>
Fecha: jueves 7 de mayo de 1998 14:31
Asunto: Re: RC Transmitter


>Zoltan Perhacs wrote:
>
>>The hard part for me is the RF stage. Can someone help me in this (40MHz).
>
   Well, you can do it as complicated as you want... PLL for frequency
sintesys, FM modulation,  various mixers, etc, or you can just build a
quartz controlled oscillator and a single amplifier stage using an VMOS will
provide as much power as 0,5W, which in 40 Mhz makes a pretty long path (a
couple of kilometres, if the receiver is stable and well designed).

   For the receiver you can use a FET input stage with either an NE602 or
SO42P mixer -quartz controlled, also-, along with a ZN414 for intermediate
frequency amplification and detection, along with a OP-AMP for audio
amplification. With these devices you can get 0,5 to 1 microvolt
sensibility, a good signal/noise (provided by the FET input stage), and also
a very little size and low power.


>Try buying a complete RF stage as a spare part. I had no problem buying one
>when I thought my Hitec transmitter was broken.
>

   Of course!


>Also, stay away from airplane frequencies unless you really know what

   Well, 40 Mhz is RC band, so there should be used. You could also use 27
MHz (very noisy, so you'll need much more transmitting power), or 72 Mhz
(pretty unstable regarding coils, and hence you'll need silver-mica
capacitors and a good RF shielding.

   Regards,

   Andres j. Ogayar

1998\05\07@102229 by Alvaro Deibe Diaz

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>Many 2-channel RC transmitters contain the Signetic chip (NE5040??) which
>is actually a 7-channel encoder.  You just need to connect additional
>pots to the unused pins.  Such a modified transmitter would still be
>"dumb," so including a PIC for digital processing makes a lot of sense.

For a simple data transmission of 7 termocouples in a electric motor (from
the rotor) I used the Signetics NE5044 (rx) and NE5045 (tx) couple. The
design was extremely easy following the data sheets, and there was no
problem with the "hard" environment. But there are little possibilities
beyond the specifications of this design. Perhaps is more convenient for
you a totally digital measure and computation of the channels... all in a
single PIC IC.

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