The simplest Serial Interface - "One resistor" serial interface

[JGT]

This is my experiencie connecting my radio to serial port to be used with FMS:
Serial port voltage levels are: Low=-12, High=+12 V, and many radio outputs are TTL: Low=0, High=+ 5( up to 9,6) V, so, in the theory, you need an interface, like the one in the manual, to convert voltage levels and connect your radio.
But in most cases, PC serial port RECOGNIZE TTL LEVELS perfectly, so, just connect radio GND with serial port GND (pin 5) and radio output pulses (through an optional resistor), to pin 9 of the serial port ( 9 pin connector), and its done !!!
I used a 680 ohm resistor and works perfect with my Futaba Skysport 6A.
/JGT

[ohioguy]

i sent you a PM about this idea.
please email me at mattclement@hotmail.com

[solo]

to JGT,

please check your PM.

rgds.

[ohioguy]

i am pretty sure this will not work.
you would have to have a rs232/ttl converter or the serial port would be very inaccurate. the serial levels are much higher that the ttl, but more importantly they are negative where the ttl are not. without some kind of converter the ttl signal would be messed up.
just my thoughts on this method of connecting up. also i looked up pin 9 and could only find out that its the "ring indicator" whatever that is.
if anyone can make me understand, id certainly love to think this works.


(Edited by ohioguy at 8:56 am on Jan. 13, 2002)

[Steve Lewin]

And don't bother trying this idea with JR radios. The output is only about 1.2V peak to peak and floats. Nothing like TTL levels

Steve

[JGT]

Ohioguy:
I will try to answer your questions:
- 'Rig indicator' is the input that FMS uses to read pulses. This input uses RS232 levels. In the theory, with a pure RS232 standard input, this 'one resistor interface' wouldn't work. But the real world is different. Most PC RS232 inputs recognize 0 volts as a logic '0' and 5 volts or more as a logic '1'. That's the reason why it works PERFECTLY !!!
- The optional resistor is just to protect your radio against a bad connection.

I've been working with this interface for weeks
with a 2 meter cable and without problems at all (no noise, no jitter ..)

Obviously, the interface described in the manual is more robust and will work with more radio types and computers, but if your radio provides at least TTL levels (0->5 volts), I suggest you try first the simplest !!!

/JGT

[Dan Kimble]

Would This "simple" interface work with my
Futaba 6DA? and if so which pin is Radio Ground, and
which is Radio Output Pulse? I Have a 6 Pin connector on
the back of my radio. Thanks

[JGT]

Dan, probably it will work.
This is GND and PULSES in the 6 pin connector of my FUTABA Skysport 6A (outside view of the radio socket). I dont know if your radio is the same (G=GND central pin, P= PULSE)

*
P *
G
* *


/JGT

[Steve Lewin]

You may need to connect the ground to the screen (metal outer) instead of Pin 6 (centre pin). For some reason Pin 6 doesn't work on all Futaba radios though it does on quite a few.

Steve

[Dan Kimble]

I tried this connection with my Futaba 6DA
with the ground connected to the center
pin and I get nothing. Going to try connecting
to the shield instead.
The 6 pin Din connector that I used had a #2
beside the pin that was suggested, is this right?
Pin 4 is directly across from it. and Ive read about using
the #4 pin. Question- Would it hurt to try the # 4 pin or
could I cook something?
any advise would be great.
Thanks Again,

Dan

[ohioguy]

pin two is signal on futaba. but im not resposible if something happens. i will wire this up and try it once i do more research on the 16550 uart and the voltage levels. if you are correct about some ports accept as zero then this might work. ill keep you posted.
thanks
matt

[Dan Kimble]

Sorry I had some cockpit problems.

ALL IS WORKING PURFECTLY!

The original pinout worked, I just didnt

have the right IRQ for my Com 1 port.

controls are smooth and steady.

[Rick H]

[MrFlower]

to JGT
Hello
My transmiter hasn´t conector with PPM siganl but I have found PPM signal into the transmiter using osciloscope, the PPM signal is 11v amplitude, appear 3 pulses, my transmiter is two channels only. is it all rigth?

Which is the best option? 16bit-DLL or 32bit-VXD

thank you

[johnhlong]

That would be the start pulse, channel 1 and channel 2.

You should be able to build the circuit that has a zenioe diode limiting the out put voltage or the transistor isolation circuit.

A simple resistor might work but if everything is not just right it may cause transmitter failure.

What operating system are you using.

John
Seattle, WA
USA