[GreenKeys] 60mA current loop

[Bill Horne]

Bill Horne wrote:
>
>>    2. If you choose to roll your own, the technical work has already
>>       been done for you, since the a member of the Morse Telegraph Club
>>       long ago designed an interface that connects RS-232 devices (e.g.,
>>       modems) to local Morse sounder circuits. Since Morse sounders are
>>       solenoids just like your machine's selector magnets, there's no
>>       need to reinvent that particular wheel. I'll provide details on
>>       request.
>>     
>
>     I'd like to see that.  

One version is at 
http://home.comcast.net/~morsekob/techdocs/loopinterface.pdf

>> If you _can't_ get your serial port to go that slow, then the plot 
>> thickens: you'll need to use ASCII characters which will translate 
>> multiple bits into a single bit position of the Baudot code. For 
>> example, you could clock out an entire ten-bit ASCII character in 22 ms 
>> by setting the UART serial clock to 454 bps, and that means that every 
>> ASCII character you sent would occupy _one_ Baudot bit position at 45 
>> baud. Assuming your serial port can be set to _not_ send parity, you 
>> could then send ten ASCII characters in place of a single Baudot 
>> character, i.e., the ASCII sequence 
>> NUL-DEL-NUL-DEL-NUL-DEL-DEL-DEL-DEL-DEL would be equivalent to a Baudot 
>> "Y" if sent at 454 baud. I know that's confusing, but it does work.
>>     
>
>     You'll still have a 4ms SPACE period at the end of each ASCII
> character, for the ASCII stop bits, so you won't be sending the
> correct waveform.  Look at the output with a scope.  It might
> work, but I wouldn't count on it.
>   
Yes, each "bit" of Baudot would be contaminated by the stop bits in the 
ASCII character - _if_ that bit is supposed to be spacing (sour grapes).

You'd have to set the range finder to favor the starting edge of the 
pulse (he said, knowledgeably). ;-)

73,

Bill W1AC

-- 
E. William Horne
William Warren Consulting
Computer & Network Installations, Security, and Service
http://william-warren.com
781-784-7287