Re: Controlling an external device with elisp

[Ed L Cashin <cashin@cs.uga.edu>]

upro <upro@gmx.net> writes:

> Jonas Steverud <tvrud-usenet@spray.se> writes:
>
>> upro <upro@gmx.net> writes:
>>
>>> Now this might be a strange question, but is it possible to control an
>>> external device, through parallel or serial port, using elisp as
>>> programming language?
>>
>> It should be possible if the device has a text-based protocol and
>> supports a tcp/ip connection. Gnus, which I use right now, does that
>> to my ISP's newsserver.
>>
>> But if you mean on a lower level, if the device is stupid, like an
>> thermometer or simple motor; I do not know.
>>
>> Depends on the device, a bit.
>
> Hi Jonas, what I meant was indeed a "stupid" device, like a selfmade
> small circuit to switch on a light or somolar (as seen in the Coffee
> mini-HOWTO).
>
> Do you think this is impossible?

No, it's perfectly possible.  The thing is that you can *use* the
device from emacs but ultimately talking to hardware is a kernel
thing.  Assuming Linux, as your reference to the Coffee mini-HOWTO
would suggest, your choices are to ...

  * build the circuit to recognize codes you can send using an
    existing driver

    e.g., you could put the device on your first serial port and
    control it from emacs by writing strings like "please turn on the
    light" or numbers like 101 to /dev/ttyS0.

or

  * use IO primitives or write your own driver as suggested in the
    Coffee mini-HOWTO

The former option is probably a lot easier in software; the latter is
probably easier for you in terms of circuit design.

-- 
--Ed L Cashin     PGP public key: http://noserose.net/e/pgp/