Problems making an universal interface

[Uitgeslapen]

Hello,

I have programmed a FMS interface, it works for my Hitec laser 4 and for a Futaba...The problem is I can't get it to work for my graupner MX-12...The signal just seem to be to weak to trigger the PIC to recognize it...does anybody have an idea how to get it in to the PIC??? Or is there a schematic out there that will work for all negative PPM transmitters?

[Malc C]

Daan,

Can you provide an image of the schematic for the circuit you are using. Also by "negative PPM" are you saying that the actual signal is from GND to -ve. My understanding of "negative" PPM signal is where the 1-2ms signals are troughs going from +ve to GND rather than peaks going from GND to +ve, which shouldn't really bother the PIC as the PIC simply triggered by the signal changing states from 0 to +ve or vice-verca, and then measuring the time before the PPm signal changes state again.

[Uitgeslapen]

Hello,

For the PPM signal...I can't get the image from my scope to the PC so took an picture..
One is from my hitec and the other from the graupner...the graupner start at a dc+ppm of 3V...the dc goes away...like on a capacitor that is decharging

I have used a lot of circuits, all work for the hitec, but can't get the graupner signal to the pic

I will post more info soon

Daan

[slipstick]

Look for any circuit designed for JR Txs. The Graupner signal is like that of all JR Txs. It is only about 3V p-p and it's not ground referenced so it just floats. You just need to tie the input signal to ground.

Steve

[Uitgeslapen]

Hello Steve,

Do you have an example of such a circuit??

These are the input circuits I have tried.. on top of the two below.. I also had one using a comparator...but no luck with the graupner tx...

I will start looking for a new solution..

THX

[Malc C]

Daan,

I use a JR X3810 for flying helicopters and for use with sims. The attached circuit works fine with FMS and my TX, so if sw follow that your MX has a signal the same (or similar) to JR TX's then hopefully this will work, or you could adapt your CCt.

The attached zip file contains the schematic and HEX code for a 12F675 PIC

The input shows a 5 pin DIN wired for use with Futaba / Hitec TX's. You will need to check out the correct pin on your MX transmitter that outputs the PPM (I think it might actually be the same as I supplied an interface at one time for someone with an MX-18 tx) - pin 2 is the PPM signal and ground the screen of the wire to the shield of the plug

[slipstick]

Daan, the second of your circuits, which basically the same as Malc's and which I've used many times, should work. One thing you might try is reversing the connections to the Tx jack plug e.g. treat tip as ground and outer as signal.

It's quite easy to code the PIC so that it doesn't matter but some of the early code I've seen still depends on the polarity of the pulses and particularly the long reset pulse. So you need to switch the connections.

Steve

[Uitgeslapen]

Hello,

I will try your idea's, I don't think it is a problem conserning the code. I have an interupt driven code, almost the same as Malc C. I indeed almost used that schematic, but I am just going to give it a go...who knows.

The only differnece is that the plug that comes out of my MX-12 is a stereo jack (3.5mm), also used for direct servo.

Further I also had a "new" idea last night using the comparator as a buffer, a pitty I was already in bed. I will keep you posted, but not today...today I build airplanes :) .

[Malc C]

Daan

According to the site http://www.mftech.de/buchsen_en.htm your TX uses a 3.5mm mono jack plug with the signal connected to the tip and GND to the shaft, which is indeed identical to JR.

[Uitgeslapen]

I am in the process of trying some new things... just builded the schematics mentioned above, I will post the results...

[Uitgeslapen]

It works!!!!!!

Thank you very much, I solved it using the input schematic of above and putting that in comparator. It think the MX-12 signal is just to small...The comparator aks as a buffer...as result I have a stable and noise free input for the pic....

You guys really helped... Thanks again

[Malc C]

Which schematic.. the one I posted or either of the ones in your post ?

Either way, glad to hear you have resolved the problem and have a working interface :)

[Uitgeslapen]

I used your input schematic, but have changed the transistor for a comparator to buffer it...now I can fly inside :) as it gets very cold outsides...

thanks again
Daan

I also switched polarity of the siganl an this has no effect

[Malc C]

LOL - I came up with that schematic as a combination of two others as I couldn't get either of them to work on their own.. one half gave good input results, the other poor, but with better voltages on the RS232 end... so I combined the best of both and it worked first time !! - Nice to see that its now been used in yet another design :)

Any chance you could post the full schematic, and share the HEX for others to try ??

Cheers

[Uitgeslapen]

I will do that, but first I want to clean up my code a bit and make a working PCB... so I know everything is OK. I redesigned the powersupply-part using a 5V regilator and some diodes. I discovered some com ports try to kill the pic.
I hope to have the pcb finished by the end of the week (if I find the time).

Best Regards
Daan

[Malc C]

Sounds good. Yes some PC's can't provide the voltages from the RS232 port, mainly laptops.

I stumbled accross this image which addresses the problem (although I've not tried it !)

http://www.qsl.net/eb4eqa/serial_booster/serial_booster.gif

Full details can be found here (http://www.qsl.net/eb4eqa/serial_booster/serial_booster.htm)

I would be inclined to use the internal +5v from the Computers PSU and fit a DB9 connector in the PC for use with the interface

[Uitgeslapen]

some pc's and laptops also can put a negative voltage on the com ports...I have blown some pics because of it...adding some diodes seemed to help. I also wanted a led that gave the state of the interface, so I needed a bit more power, so I used more lines to get the power from...

Flying FMS is fun :D (not really the same as the real thing)

[Eric Brouwer]

I hav ebeen using this circuit for the past 4 years, and it works 100% with all leading brands of transmitters.