Re: Controlling SCR firing board: PWM or potentiometers


Ignoramus28584 wrote:
On 26 Jun 2006 07:04:44 -0700, Luhan <luhanis@xxxxxxxxx> wrote:

Ignoramus28584 wrote:
On Sun, 25 Jun 2006 18:05:41 -0700, Tim Wescott <tim@xxxxxxxxxxxxxxxx> wrote:
Ignoramus8946 wrote:

I have an SCR firing board controlled with 0-5V potentiometer input
and separately a microcontroller. This microcontroller can output
0-5v.

I have a dilemma. I can either:

1) Let the pots control SCR firing board output, and let the
microcontroller simply turn it on and off

2) Let the PWM outputs (filtered to DC) control the SCR firing board.

Which is best? In the long run, 2 is more versatile and could allow me
to do fun stuff like TIG pulsing, "Lift Arc" starts without high
frequency, etc, with just some BASIC programming.

On the other hand, it is a little more dangerous if I make a mistake
in code (which sometimes happens ;).

A common sense approach would be to wire the board so that I have two
sets of outputs, PWM and pots, and connect SCR firing board to pots
first. When I get some tig welds done, etc, I could experiment further
with PWM control of the board.

What am I afraid of? That I make a mistake and programming and somehow
the welder would go very crazy.

Is what I am saying, making any sense? Any words of wisdom?

i

Have someone else, preferably someone you don't really like, test new
code for you?


That's a good idea, but no, no one else tried it.

Anyway, I got the PWM output to work. (meaning that there is output,
not that the SCR controller likes it).

My programming is basically done and so is wiring of this control
board. I will do some final testing tonight.


I'm not sure just how this may apply to your situation.

I do all the fancy control stuff with micros, and all of the safety
stuff with simple electronics or mechanics. In other words, design so
you can survive a microcontroller failure.

Yeah. I really like your approach.

What safety stuff do you mean that you do with simple electronics or
mechanics?

I definitely want to first use regular pots for voltage and current
control, until I get my first welds.


I've used microswitches to directly cut motor power at the travel
limits of servos.

Fuses or circuit breakers for maximum current cutouts. In some
instances, incandescant lamps in series with power feeds: their
resistance swings up under high current loads.

Ground Fault Interruptors feeding power to my test bench outlets.

I don't know your entire situation - just keep any safety stuff as
foolproof as possible.

Luhan

.

Relevant Pages

  • Re: Controlling SCR firing board: PWM or potentiometers
    ... and separately a microcontroller. ... Let the pots control SCR firing board output, ... Let the PWM outputs control the SCR firing board. ...
    (sci.electronics.design)
  • Re: Controlling SCR firing board: PWM or potentiometers
    ... and separately a microcontroller. ... Let the pots control SCR firing board output, ... Let the PWM outputs control the SCR firing board. ...
    (sci.electronics.design)
  • Re: Controlling SCR firing board: PWM or potentiometers
    ... and separately a microcontroller. ... Let the pots control SCR firing board output, ... Let the PWM outputs control the SCR firing board. ...
    (sci.electronics.design)
  • Re: Music Student in Need of Help
    ... I wish to replace the analog Pots in my distortion pedal with digital ... equivalents so as to control it in real-time from a computer. ... You might even be able to sale the pedals if you ...
    (sci.electronics.design)
  • Re: 59 deluxe...project
    ... Would it seem that this is normal, do I need to go back through the input, and control sections again? ... I know it was hell to get solder to stick to the back, to ground them like pots in a guitar. ... This time they started the second team, that didn't help the first team motivation, then the first team had to dig them out of a 2 touchdown hole. ... I being ne who never does anything the easy, and usually the right way, just used Hoffman Amp's layout as a reference tool. ...
    (alt.guitar.amps)