What To Do With A Dead Pro Line... - RC Groups
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Nov 05, 2012, 09:58 PM
Experienced Balsa Mangler

What To Do With A Dead Pro Line...

The attached photos show my situation, and my potential solution...

I know, the photo of the insides -- rather, the lack thereof -- is just sad. Almost sacrilege. I acquired this Pro Line Challenger 5 about 23 years ago, in a swap-out for my ACE Digital Commander 7, and IIRC, it still had the encoder board at that time. The encoder board was lost to history awhile later. Chalk that one up to a complete lack of understanding the history...

Notice in the foreground the schematic of a "new" encoder. Notice, too, the Futaba FM module on Channel 20 sitting between the "donor" and the potential recipient...

I say "new", only in the sense that I want to build a new encoder board for the Pro Line. Thing is, I want to use an older generation design. The circuit I'm considering is pulled from several Kraft and Heathkit schematics of the late '60s and very early '70s. The general idea is to feed the output of the encoder into the Futaba FM deck. This eliminates the issue of messing around with RF circuitry...

Before going deep here, I have looked at the new MS2K encoder and think it might be a good project... for later. What I'm wanting is a really retro-classic style of encoder for an old case, where the fanciest bit of operation is just getting the servos to wiggle properly.

Getting seriously technical here...

If I have read the schematic of the Futaba FM RF deck correctly, it has an internal 10K resistor pulling "up" the modulation line to Vcc, meaning I need an open-collector NPN to drive the pin. Using the Kraft/Heathkit diagrams as a starting point, they invoked a pair of PNP switches to form the monostable pulse shaper. With the second switch in the "stable-on" mode, this provided a positive-shift pulse output to the original RF deck (framing pulses were negative-transitioning). If I use this circuit, then I believe I need an NPN pulse inverter hanging off the second PNP's collector to feed the Futaba deck, thus flipping the positive-shift signal to a negative-shift signal as needed by Futaba receivers.

Diving deeper, I think I can eliminate one transistor (final driver) if I change from PNPs to NPNs in the monostable, then use the input pulses (negative-transitioning) to turn the second switch off. And, if I leave that NPN's collector open, then I achieve the same result as before.

Does anyone find a problem with this idea? Have I missed anything important? I'm very much open to suggestions, especially from anyone who's built something similar.
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Nov 06, 2012, 07:34 AM
I bail out, anywhere, anytime
Taurus Flyer's Avatar
C.P. mc Graw

Two points to think about.
First, the old encoders normally do need the use of old style servos. Reason, the centre position of the stick (pulse) often isn't 1,5 ms. The old style servos do compensate the non linearity of timing.

Second point of intereset is cmparing of the diagrams.
The inverter transistor also does create the ramps to switch off AND on the rf signal. Often this is needed to reduce the bandwidth of the output of the transmitter. See the diagrams.
In general, not knowing details!!! See also G013!

Nov 06, 2012, 09:21 AM
Experienced Balsa Mangler
Taurus Flyer,

Thanks for the reply on the pulse shaping circuit feeding that NPN final. I seem to recall from my senior-year HS electronics course (33 years ago!) something about how square pulses had lots of unwanted harmonics. It seems this project is blowing the dust off of more than just an old case...

One of the Kraft circuits used a two-transistor PNP configuration for the final, and that's what prompted my second circuit idea. Granted, those old systems were all AM, and I'm trying to go FM with this project. Not having a sillyscope at present isn't making this any easier...

I'll start exploring shaping filters for the next revision.

I do plan on using modern servos and a Futaba-style receiver with this transmitter, so I appreciate what you said about the old servos. More research...
Feb 12, 2013, 10:49 PM
Experienced Balsa Mangler
In the time since I last posted to this thread, it seems FrSky has released a DIY module for older transmitters which can interpret the output signals from any encoder (positive or negative shift) and link up with one of their own receivers. Although other projects have taken priority, I am still interested in trying this out. I'm not committed to using the "old school" encoder design, but it's still something that appeals to me. It's worth a try, at any rate...
Feb 13, 2013, 12:50 PM
Registered User
jhaywood's Avatar
Where did you see the DIY FrSky module? I have a ProLine Super Compition Six that I would like to convert.
Feb 14, 2013, 12:49 PM
Registered User
Aloft sells the DTH-U modules in the USA, he is a straight up guy.

If you really like micro computers and programming I would stick an Arduino in it with a DTH-U telemetry unit and start programming. There are some threads on here about Arduino encoders.

Could use an encoder from a 9X and interface it to a module and use the installed firmware or load the board with a version of the open source 9X firmware

Otherwise an encoder board from a JR6103 or 7202 would make a nice system and will talk to the DTH-U module.

If you need Spectrum then use the guts from the Orange Hobby King Spectrum module.
Feb 14, 2013, 02:19 PM
Registered User
jhaywood's Avatar
How do you determine what the PPM output line is on something as old as my Proline? What should I look for? If it was modern, I can just look at what others have done, but i am not too sure what I am looking at inside this old radio. No chips, no LEDS, LCDs, no buttons, notta!
Feb 16, 2013, 08:43 AM
Registered User
Can you post a picture of your encoder? Both sides would help.
Feb 16, 2013, 12:16 PM
Registered User
jhaywood's Avatar
Here are the pics. The bolt with wires is the antenna mount.
Feb 28, 2013, 08:19 PM
Registered User
richardojohnson's Avatar
Ihave a ton of old proline and ace sevens what can I do with them.I still fly one on am but were in an area that does not seem to have any interference any sugestions
Feb 28, 2013, 08:26 PM
Registered User
jhaywood's Avatar
Radio south can covert them to Futaba FASST. I wouldn't mind taking a couple off your hands, especially if you have a single stick.

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