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

[Dave Philipsen]

On 12/25/2015 12:09 PM, RETRO Innovations wrote:
> 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.
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>
> 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.


Exactly.  That's what i meant when I said, "wire an LED to a handshake 
line" (in message above).


>
> 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
>