[Coco] Plugging more stuff in to the RS-232 Pak

[RETRO Innovations]

On 12/25/2015 10:21 AM, Dave Philipsen wrote:
> I would say it's within the realm of possibility.  I suppose you could 
> somehow wire an LED to a handshake line and do it.  I once wrote some 
> code to do exactly what you talking about.  It wasn't on a CoCo but I 
> bit-banged an output bit on a 68HC11-based device to create the signal 
> for an IR LED which controlled a NTSC video printer.
>
> Dave
>
>
> On 12/25/2015 8:06 AM, K. Pruitt wrote:
>> Is it possible to power an IR LED via the RS-232 pak and successfully 
>> send a set pattern of signals to an IR-controlled device?
>>
>> In other words, can I use my RS-232 pak to turn my CoCo in to a TV 
>> Remote? I have no idea at what "baud rate" those signals are sent 
>> out. Can the CoCo match the speed? I'm guessing yes.
>>
>> Certainly someone has tried this already, if it isn't just out and 
>> out stupid. It sounds pretty simple. A resistor or two and an IR 
>> LED?  I have a bazillion remotes around here I can pull an IR LED 
>> from. Am I going to blow up my CoCo! Hehe.
>>
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>
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It is, but you should approach it a bit differently than I think you're 
considering.

Most IR receivers won't accept RS232 signals, so you'll not have much 
luck with putting the IR LED on the TXD pin.

What will work better is putting the IR LED on the RTS pin.

You can then bit bang any signal protocol of interest, as you have 
direct control of the LED

poke &HFF6A,4: REM IR LED ON
poke &HFF6A,0: REM IR LED OFF

On the DE-9, I'd not wire the LED directly to the RTS pin, as LEDs don't 
have great reverse breakdown current capacity, and RTS swings between 
+12V and -12V.  I *think* a register 1n4001 in series would work, so, 
I'd put the diode in first, put the led onto it, and then a resistor 
(assuming the LED has a forward breakdown voltage of 1.7V, and uses 
20mA, use (12-.7-1.7)/.002 = ~5K resistor) and then ground.  Since RS232 
signals are reversed, and I have not played with RTS for a bit on a 
6551, you might have to use 4 to turn the LED on and 0 to turn it off.

Of course, then you have to write some ML to bit bang the pin to create 
your protocol.  Have fun!

Jim

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