I am trying to feed a PWM signal into a welding machine to control its power and I do have a major problem: the PWM should swing between +V and -V and not from 0V to +V as in the arduino output.
Is there a (possibly simple) way to shift the output voltage so I can have it going from (say) -12V to +12V?
PWM input has only two wires so the voltage must truly reverse (i.e. a voltage divider would not work as I do not have any place where to connect the virtual ground)
thank you for your responses, as always this place is a source of many good answers
Yes you can have it at any voltage you like. The old TTY machines used +/- 75V.
plus the duty cycle increase and decrease as you expect from a PWM??
That waveform you posted did not show the duty cycle of a PWM signal. It looks like you are confusing the data signal, which will be sending an increasingly large number with increasing power, with PWM which will have a constant on / off ratio signal for any specific value.
I am trying to feed a PWM signal into a welding machine
We have had many welding projects on the forum over the years and they all suffer from EM interference to the Arduino causing it to miss-behave. I am not sure if the people making the projects ever solved that in a satisfactory manor.
well, what to say... this is a very interesting idea of that being not a PWM signal, but the screenshot in the picture was taken while the regulation was in action, so I would expect that thw square wave would open and close like that... so the question now is: how can i check if that is an RS232 signal? any way to do that?
no the controller is NOT in the machine… it is a separate external box that reads the temperature and supposedly feed in the commands to lower and rise the power… attached another screenshot of the signal out of this extarnal controller
there is a welding machine (induction heater) the heat up the part. this machine has an input to control the power applied
an external device reads the temperature with a pyrometer and apply the correct settings to the heating machine to keep temperature constant
this second device is what i am trying to replicate, as they are 30 years old and no longer available to be replaced or repaired
so far i managed to have a good reading of the temperature and i do have a PID controller that supposedly would keep the temperature constant on the part. from the second picture I posted I was convinced that was a PWM so I made an output accordingly, but applied on the machine it is NOT working. Needless to say I did not notice at first sight that it was using negative voltage as well (the machine is located in italy and i am in england) so I do not have any way to directly access the machine and measure)
being that i sent the box and it is not working i asked them to call again the guy with the oscilloscope and measure again, and the first picture i posted was the result of that
thank you Paul... i will look into that.
I have no way to tell how they set the oscilloscope, but can you please elaborate on that? what would be the difference in reading? I am more a programming guy than an electronic wizard lol