Re: [ATM] Making glass blanks

[martin.cibulski@t-online.de (Martin Cibulski)]

Stuart,

> . . .
> Latching the output byte from the printer port is trivial.  Converting the
> byte to an analog voltage representing the setpoint is trivial. Comparing
> the setpoint voltage to another voltage  representing the temperature from
> the thermocouple and turning the solid state relay off and on is also
> trivial.
>
> This is the control scheme suggested by Martin Cibulski.

Do you mean that the comparison between setpoint and measured temperature
is done in a controller outside the computer ?
Then I suggest a different solution.

I would do everything in the computer without an external controller.

The computer reads the temperature value and compares it to a setpoint
inside
the software (which in turn is changed slowly for the annealing process).
The temperature difference is used as input to a PID control algorithm.
The PID's output (usually scaled as 0-100%) will be translated
into a pulse width modulation which can be slow and so handled
in software even under Windows. A 5 seconds PWM cycle with 0-5
seconds on time in each cyle will be fast enough for temperature control.
The on/off signal from the PWM can be written to one BIT of the printer
port. This bit is used to switch the solid state relais.

So no external temperature controller is needed because the controller
is part of the software. Only one solid state relais must be switched
directly from one bit on the printer port.

Regards,
Martin Cibulski

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