Parallel Interface

[hebi]

Hi Guys

I was trying to get PPJoy running on my PC, together with a Grupner MC14 control. I found that the Interface cable with the Zehner diode does not work because the RC control is not activly pulling down it's output when outputing a "Zero".

I have now replaced the Zehner circuit with a NPN transistor pulling down the IRQ line of the Parallel port and a series resistor on the Base of the transistor.

Now everything works fine. Is there any intrest in the schematics of this? Whre can I send it to be published?

Herbert

[brettbear]

Hi,

He's right... the zener/resistor method has no right to go in nearly all cases. (Discovered this @ 4am Monday morning) Always use a transistor instead. Can't post a pic anywhere on the forum that I can work out... I have one available...

The basic circuit is this...
Choose a NPN transistor with gain of 100-500. (e.g. BC548 or 2n2222 as shown elsewhere in the forum...)

The emitter of the transistor connects to GND of the TX and also PIN 18 on the para port.

The collector of the transistor connects to PIN 10 of the parra port.

Connect a 4k7 resistor to the base of the transistor.
The other end of the 4k7 resistor connects to the PPM pin of the TX.

This will result in the transistor pulling the parra port interrupt line low, registering a PPM pulse.

In my limited tests, polarity of the PPM signals seems not to matter. I also tried a PNP transistor (swapping the collector and emmiter of course) with identical results.

My Futaba t6exa loves the sim, as do I... but have to upgrade the computer now to make full use of the sim... oh well... there are worse problems...