Interface not working - help please - Multiplex 3030 - seems it should work.

[ehart]

Hi,

I have a Multiplex 3030, and have built the simplest parallel circuit shown in the manual. I used a 410ohm resistor because my radio has only 6 cells - nominal 7.2v - and I interpreted the instructions (correctly?) to mean that lower voltage means smaller resistor. I used a 5.1v Zener diode because the 4.7v wasn't available. Using 7 feet of coax cable.

On the transmitter side, I used MPX plug description from another website (pin 4 = signal, pins 5+3 tied together to ground). This seems to work, in that RF is disabled by 5+3, and there is a voltage on pin 4.

When it's all said and done, I get +3.8v on parport pin 10 (measured across Pin 18). So I thought I would be good to go, but the calibration in FMS shows nothing when moving the sticks, and TXINT shows no sync pulse. INTTEST fails. TXINT has a few times after running for a while generated a Win98 blue screen saying that it's attempting to use a resource that's in use, but not since I disabled just about everything else.

I don't want to make this message too long, so I won't list everything I've tried (unless asked!) but it includes disabling many devices in Device Manager (including SoundBlaster 16 PNP card), ECP and EPP parport settings, confirming port is set at LPT1/port378/IRQ7, disabling Antivirus and print drivers, and trying 16-bit and 32-bit settings in FMS.

Gosh, what's left?

-- Should I try an even smaller resistor? Or am I on the wrong track there?
-- Is there a way to measure the current on the circuit? My DVM will measure milliamps - what value am I looking for? Maybe there's not enough "oomph" here?
-- I will get a loopback to test the parport operation on the machine.

I can't think of much else to try!

Thanks for reading this!

- Eric

[ehart]

Well, I got it working.

My advice to fellow MPX 3030 owners -- buy Ken Hewitt's PIC interface. I spent almost as much in parts as he charges for his kit (as much or more if I hadn't had some parts hanging around), and the resulting interface isn't really jitter-free, and won't work with XP or 2000 when I upgrade my computer (his interface is better on both counts). Here's the link:

But that's not what I did. Based on August's success, I built the interface described here: I followed the pictures and used the exact Radio Shack part numbers for the transistor and resistor. It is just as simple to build as the zener diode/resistor plan shown in the FMS manual (same number of parts -- 2!).

I'm quite sure I built the original cable correctly, and I think based on my experience and August's comments, I don't recommend trying the zener diode/resistor plan shown in the manual. Either do what August and I did, or even better, buy Ken's kit.

- Eric

[ehart]

p.s. If you build the cable I did (rather than taking my advice and buying Ken's!), you will need this link to show the Multiplex connector:



"From the rear" means from behind the plug as it goes into the transmitter.

The "Pico" interface shown here works fine for the MPX 3030.

- Eric

[ehart]

p.s. If you build the cable I did (rather than taking my advice and buying Ken's!), you will need this link to show the Multiplex connector:



"From the rear" means from behind the plug as it goes into the transmitter.

The "Pico" interface shown here works fine for the MPX 3030.

- Eric

[uschuett]

Eric,

got the same problem with Harald Sattler´s par. interface described in the FMS manual. Didn´t work. PPM signal from my robbe terratop TX was as low as 2,0V (peak) checked by osci.

Changed the design to the transistor augmented type described in the manual for JR TX that has a low voltage ppm-signal too. Works like a charm now.

The net´s best description for construction of the par port interface with lot´s of excellent pictures is on eriq´s heliguy page:



I think it´s the same page you referred to but a slightly different url.

Many thanks to Michael and Roman for providing the great FMS program.

Ulrich

Holm- und Rippenbruch!