David Tayler Posted March 17, 2017 Share Posted March 17, 2017 I am trying to interface a TOY-MTX module for flying an EAchine E010 to a Futaba FF9 transmitter. The module works perfectly with my Taranis. The pin out for the Futaba is 1 ppm out 2 V+ 3 RF detect 4 GND 5 RF out. Taranis is 1 ppm out 2 UART 3 V+ 4GND 5 Sport.. With an oscilloscope between pins 1 and 4 on Futaba the signal is only a few mV and highly differentiated. Can anyone explain or help ,Please. Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted March 17, 2017 Share Posted March 17, 2017 "Highly differentiated" - sounds like a poor connection somewhere, and you are just getting capacitive coupling. I'm not familiar with the Futaba pinouts - are you sure you have the pins correctly identified? -- Pete Quote Link to comment Share on other sites More sharing options...
David Tayler Posted March 17, 2017 Author Share Posted March 17, 2017 I have checked the pin out. I agree it looks as though all I am seeing is a capacitivly coupled PPM signal but the 'scope probe was connected directly to the pin ,just via an 0.1 inch socket.I used two different sockets just to check. Got the same result both times. Quote Link to comment Share on other sites More sharing options...
Chris Bott - Moderator Posted March 17, 2017 Share Posted March 17, 2017 Could you possibly need a pull up or pull down resistor David? Are you sure you have the right pinout? Here's one I randomly found on t'internet Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted March 17, 2017 Share Posted March 17, 2017 OK, but what about the ground pin? Does what you see on the 'scope change if you remove the ground connection? -- Pete Quote Link to comment Share on other sites More sharing options...
David Tayler Posted March 17, 2017 Author Share Posted March 17, 2017 Chris, It is not the buddy box connector that I an using but the five pins in line ,which are used for RF modules that plug into the back of the transmitter,Thanks for looking on the net though. Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted March 17, 2017 Share Posted March 17, 2017 Surely David, the complete package, ie correct Amplitude, is at the final stage, from the antenna Is the socket not just a "shortcut" to the board output Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted March 17, 2017 Share Posted March 17, 2017 David - have you checked the ground connection? What you are describing would also be cause by no or a poor ground between the 'scope and Tx. -- Pete Quote Link to comment Share on other sites More sharing options...
David Tayler Posted March 17, 2017 Author Share Posted March 17, 2017 Dear Pete, I presume the ground is OK as the module is being supplied with the full battery voltage when measured on the module board.However I will check with an ohmmeter when I get my hands on the transmitter again. Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted March 17, 2017 Share Posted March 17, 2017 David, you are missing my point somewhat! On the face of it - and assuming you are connecting your 'scope straight across the transmitter pins - this looks like a fault in the transmitter. However, that is fairly unlikely, and before ripping the transmitter open, you really want to be sure you are not being misled by a poor connection between the 'scope and Tx. A faulty connection between the 'scope probe ground and the transmitter would also give the symptoms you describe, and would not be shown by the 'scopes test / calibration point. Hence my question, does the trace change when you remove the ground? (Switchable X1 X10 'scope probes are notorious for this!) If there is no change, then the 'scope connection is faulty. The final check is does the Tx work OK with its own module? If so, then the Tx is not at fault. Some modules are very fussy about what you feed them. The Taranis is switchable between +ve and -ve going PPM. I have a feeling it defaults to negative, but its been a while since I changed mine! I think Futaba is positive going (I rarely see Futaba transmitters, and don't have one to check.) Some modules are also fussy about the width of the pulses supplied, but these are very much in a minority. They do still work, but the neutrals shift a bit! Before you start trying to fix the transmitter, make *really* sure that's where the fault lies! -- Pete Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted March 17, 2017 Share Posted March 17, 2017 FF7/8 and 9 sometimes suffered from poor connections in the module bay, the pins usually just needed the soldered joint to their PCB refreshing. IIRC it was more common if modules had been swapped a lot. I learnt this when I was using FrSky modules in these transmitters. Quote Link to comment Share on other sites More sharing options...
GONZO Posted March 17, 2017 Share Posted March 17, 2017 This any use? Note comment about resister between pins 1 and 2. Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted March 18, 2017 Share Posted March 18, 2017 Good find, Gonzo! A "pull-up" resistor from the PPM output to Vcc may well be needed for this module. I'm still puzzled by the "differentiated" appearance of the pulses, according to the OP. Without a pull-up resistor, you usually see very tiny, but correctly shaped pulses, whereas he is describing spikes where the edges should be. Also some modules (early FrSky hack modules, for example) could be damaged by having a pull-up, and actually required the opposite - a diode in the line to prevent the voltage rising above the internal (regulated) voltage of the module. Bob's point about the pins suffering from weak soldering is also very true - especially if a lot of module-swapping has taken place. But opening up a transmitter can be quite fraught - lots of wires between the front and rear case, switches holding things together, etc - which is why I don't recommend it unless you are *really* convinced that that is where the fault lies! Check everything else first! -- Pete Quote Link to comment Share on other sites More sharing options...
GONZO Posted March 18, 2017 Share Posted March 18, 2017 Not a problem with the FF9, just unplug battery and remove before unscrewing and removing back plate. The module pins and the trainer socket are mounted on a sub board that's left with the main body. IIRC there may be a few wires(battery charge socket) but no problems with switches etc. Quote Link to comment Share on other sites More sharing options...
David Tayler Posted March 18, 2017 Author Share Posted March 18, 2017 Dear Peter, Thank you for your further explanation of what you ment by checking the scope to ground connection.I understand now exactly what you meant. As the transmitter works with a FrSky module and is not mine anyway,I wont be opening it in a hurry! I think a pull up resistor will be my first shot this morning.10k for starters.Many thanks to all for their inputs. David Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted March 18, 2017 Share Posted March 18, 2017 Keep us posted as to how you get on! Good luck! -- Pete Quote Link to comment Share on other sites More sharing options...
David Tayler Posted March 18, 2017 Author Share Posted March 18, 2017 Dear All ,a 10k pull up resistor is the amswer,I now have a lovely pulse waveform of 9volts amplitude.Many thanks for all the comments and expertise. What a very useful forum this is. David Quote Link to comment Share on other sites More sharing options...
Chris Bott - Moderator Posted March 18, 2017 Share Posted March 18, 2017 I wish I'd mentioned that earlier, haha. Good news, well done David. Quote Link to comment Share on other sites More sharing options...
Peter Christy Posted March 18, 2017 Share Posted March 18, 2017 Excellent! The old FM modules tended to have the pull-up in the module, as it formed part of the modulating circuitry. So do many of the 2.4 GHz plug in modules, so that they can work with 35 MHz transmitters. Looks as if your module didn't do this! Anyway , good result, and well done to Gonzo too for spotting it! -- Pete Quote Link to comment Share on other sites More sharing options...
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