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Jul 02, 2004, 07:46 AM
Registered User

Make a pc joystick out of an old transmitter??

Hi everybody!

I was just wondering if its possible to build a joystick for my computer out of an old unused 4 channel transmitter.
My motivation: I dont want to spent money on an interfacecable for my Tx to train on a sim like fms.
My thoughts so far:
Cut of the cable of an unused joystick with gameport-connector.
Connect the wires of the cable with the potentiometers of the transmitter. Voila! Ready to fly.
I have to remark i am a noob in electronics so please dont laugh if it is a stupid question.

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Jul 02, 2004, 08:57 AM
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plane_spotter's Avatar

have a go

I am sure it is possible, but seems like a lot of work. It would be more practical, if the tx works to i/f via the buddy box port. You only need a piece of cable, a resisitor tansistor and suitable connector to connect via serial or parallel. Goto FMS homepage and look at the links. There are pages which should answer all your questions.

Hope this helps.
Jul 02, 2004, 09:25 AM
Registered User
I would prefer my method if it works. It would be very comfortable for me when i have a joystick looking like a "real" transmitter permanent connected to my computer. During weekdays i live in a small flat near a university where i am studying civil engineer and where my computer is. I dont want to take the transmitter with me after the weekend. So thats why i would prefer my method. I am trying to build something like this:

I opened my (unused) old joystick. The wires of the cable are directly connected to the potentiometers. And the cable goes straight into the gameport of the computer. If i rebuild this on my unused transmitter (with the potentiometers of the transmitter) it should work or? There is nothing else to do than soldering the wires to the potentiometer? Just to be sure ...

Jul 02, 2004, 10:32 AM
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JWags's Avatar
I've tried this, and not had much success. The game ports on PCs sense the current going through the pots, instead of using them as a voltage divider.

PC joystick pots seem to need to be around 100kΩ to work properly, and the few transmitters I've taken apart all have 5 or 10kΩ pots. I've tried this with quite a few ('70s Cannon, '90s Futaba, new Hitecs), and never gotten satisfactory results.

I even bought a joystick-to-USB port, thinking it would be more forgiving, but I had no luck.

I used a Dremel to shape a 100kΩ pot shaft to work in an old Futaba TX, and got fairly far, but then a two-stick analog USB hand controller appeared at a local electronics store for US$10, so I bought that and gave up (I do that a lot ).

It was fun to experiment with. I found quite a few helpful links on the internet, but they're on my computer at home. Here's a familiar one I found on Google searching for "PC Joystick Schematics"
Jul 02, 2004, 11:06 AM
Registered User
If your old transmitter works (to some degree), and you can get at the pulse signal (either through a buddy port, or scoping it to find the right pin), you could just interface with it directly.

SmartPropo is a pretty cheap interface to build, a cable from a pair of headphones, and a resistor is all you need. You could probably scavenge all these parts for free somewhere in the university.

Jul 02, 2004, 11:08 AM
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Mr.RC-CAM's Avatar
I dont want to spend money on an interface cable for my Tx to train on a sim like fms.
As mentioned, the Tx's stick pots will need to be swapped for 100K to 1M ohm pots. Here is one such hack:

BTW, the popular FMS Tx interface cable can be built for under $5. Even the PIC based ones can be that cheap if you have access to a PIC Chip programmer. If you have the skills to wire the pots and connectors then you probably have what it takes to build the circuit based solution. It is really the way to go.

Jul 02, 2004, 02:57 PM
Registered User
Thanks for all the info!
I will have a closer look to my Tx this weekend. So i can decide which of the suggested ways to go.
Very useful links provided here. Thanks.
I will keep you updated in the next days after i had a look into my Tx.

Jul 09, 2004, 06:37 AM
Registered User
I had a closer look into my old Tx. I measured the potentiometers. they are far away from 100 k ohm and they have to be changed to work with the gameport. but thats to much fiddling to do.
So i decided to build the interface cable described in the manual of FMS and here (if you can read german) for the parallel port. there is only a resistor and a diode needed to build this interface. and with PPJoy it will simulate a joystick. Sound easy

Aug 16, 2004, 01:25 PM
registered user
Retlaw's Avatar
If you want to convert a transmitter into a joystick be using the original potmeters ( +:- 5K Ohm ) it is possible if you are feeding the game port with a voltage and not with a current, It realy works !! I am using it with FMS and IPACS adding a few ( f.i. 3 ) push-button and you can use it as : landing gear up or down. in other simulators to shoot etc.

groeten Walter
Last edited by Retlaw; Oct 14, 2005 at 01:03 PM.
Aug 17, 2004, 08:17 PM
Registered User

This is something very new. Could you provide more details as to how this works? I did a search for info on the joystick port, but could not find any detail technical info relating to this. Only that voltage is converted to frequency pulse by a circuit. I just need to under stand this before I will hook it up to my computer. Your diragram is perfectly clear. I would have no problem wiring it up. Thanks.
Aug 18, 2004, 06:50 AM
registered user
Retlaw's Avatar
When i said feed with a voltage and not a current it is perhaps confusing, it is not "realy" voltage but a current
It is save to use this, because you are never going higher than 5V, there are only a view degrees used of the pot.meter, on the soundcard there is a resistor and a capacitor determining the pulse frequency, measured by the software . I don't know in detail how it works, but it works. I have done the first tests with a resistor ( 10KOhm) in serie with the output of the pot.meter, but then the readout is going up and down i.o.w. not fine enough to fly with a 3D plane. So finaly it ended up without a resistor in serie.
Tip : you have to turn the hole transmitter pot so that the ground is as far as possible away from the pot. middle. ( start with the potmeter in the middle and look in the joystick setup-test for the results )
Groeten Walter
Last edited by Retlaw; Aug 18, 2004 at 06:56 AM.
Aug 18, 2004, 03:23 PM
"Simplify, then add lightness"
The reason your circuit would work, is that there is an internal series resistor in the sound card of around 2k that will convert the voltage back into a current. The original joystick port on a PC had a 558 timer ic, with a capacitor to ground which was charged thru an internal 2k resistor in series with the joystick pot to 5volts. The PC discharges the capacitor, then measures the time it takes to charge up to about 2/3 of the 5volt supply. The important thing with the circuit you show is to make sure the pot is always at least 2/3 on. With the pot wired like you show, anytime the pot was turned less than 2/3 up, the cap would never charge to 2/3 of the 5volt supply. I don't know how the game ports in the current integrated chipsets work, but I have seen at least a few that still have the equivalent of a 558 timer.
Aug 19, 2004, 10:26 AM
registered user
Retlaw's Avatar
Thanks Jeffs555
it is already a long time ago i have made the TX conversion, and its coming back in my brains , you must arive above the trigger voltage
groeten Walter
Last edited by Retlaw; Sep 11, 2004 at 01:13 PM.
Mar 01, 2006, 03:11 PM
Just call me crash.

Hacking a BCX TX for a sim?

Sorry for dragging up such an old thread but did a search and found nothing that answered the question. I tried this in the microheli forum with no satisfaction.

Is the information in this article still valid, and can it be applied to the BCX TX for a flight sim controller? From what I hear, the E-Flite TX is a restickered Futaba.

Of course, knowing that the TX will no longer **be** a TX.
Mar 01, 2006, 04:37 PM
Registered User
If you wanted a USB interface, the following are appropriate:

Interesting detail - these implement a USB device without using a USB specific microcontroller.

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