Futaba "Challenger" PPM Output

[aesmith]

Hi,

I have an old Futaba Challenger 5 channel transmitter. It's retired from active service as I had some reliability problems and also because I've moved onto a newer "computer" set. I was thinking of converting the Challenger into a dedicated simulator controller, but it does not have a trainer socket. I was wondering if anyone knew where to pick up the PPM output and appropriate signal ground. It might be handy also to know how to disable the RF transmission, but in fact I think removing the crystal will do that.

Ta in advance, Tony S

[RCModelReviews]

Removing the crystal will stop the transmitter from transmitting.

One place there's almost always a PPM signal on an FM transmitter is on one side of the crystal. However, whether the voltage of that signal is going to do the job is another question -- but you could try it. Just put a 10K ohm resistor in series with it in case the voltage is too high for whatever you're going to plug it into.

[aesmith]

Cheers, I'll check that out. The crystal is on a daughterboard inside the case, connected to the main board by a 5 pin connector. I'm thinking that the daughterboard is the RF section (to suit making the transmitter in 35/40/72MHz versions) and if that's the case I guess there's a good chance that the PPM signal may be on one of those pins.

It will connect to the Mic input on the PC sound board, so I'll need to put something in as you suggest to protect both sides.

[Rex]

OK, the solution is easy. I've done a mod to mine and used it with the FMS software. Here's what to do:
If you look at the smaller circuit board (LHS looking at the Tx with the case back removed) you will see a white 5 pin Molex connector down at the bottom RH corner (the connector joins the two boards). To the left of this connection is a wire strap between pins 2 and 5 - this is the 'earth' contact. Further to the left you will see a vacant pcb hole between two resistors; a pos connection is soldered to the pcb here. The 'earth' wire goes to the outside contact of a jack socket (I used a 2.5mm jack mounted on the RH case panel corresponding to the LH panel for the channel 5 switch) and the 'pos' wire goes to the centre contact. Plug your lead to the sound card 'line-in' socket in to the new jack. That's it !
If I could post pictures here it would all be so much clearer to follow but hopefully the above description will make sense to you.
Good luck !

[aesmith]

Thanks for that. I don't have the transmitter in front of me but that description sounds completely clear. Did you put any protection or limitation on the signal to FMS? Like a resistor in series or series/parallel to drop the voltage? I'll have a little measure I think.

[Rex]

The position in the circuit at which the ppm signal is accessed gives adequate protection. I've used this mod for an FMS link for a year or two as well as using the Tx for flying. No problems at all.
It's probably best to remove the xtal when in simulator mode but it doesn't seem to be absolutely necessary.
I've just made the jump to 2.4GHz so looks like the Challenger 5 (actually now modded to 7) will be taking a back seat.