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Forum Index : Microcontroller and PC projects : PWM to +/- 10V

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Tinine
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Joined: 30/03/2016
Location: United Kingdom
Posts: 1646
Posted: 06:56am 17 May 2022
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Actual DAC signal:








Craig
 
Turbo46

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Joined: 24/12/2017
Location: Australia
Posts: 1593
Posted: 07:04am 17 May 2022
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Hi Peter,

That 100Hz is the upper 3db point, the input 0.15uF capacitor has an impedance of about 100 ohms at 10kHz so that should be insignificant.

Bill
Keep safe. Live long and prosper.
 
Tinine
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Posted: 07:06am 17 May 2022
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  PeterB said  Bill.

I think that Craig's circuit is part of a servo and would need a response down to d.c.
I may be wrong.
He hasn't tested my circuit yet after all the hours I spent wearing my slide rule down to the bone. These young blokes have no respect for we old people.

PeterB  



Au contraire :)

I value any/all contributions. Am about to hack this older prototype to try the various options  


 
PeterB
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Posted: 07:15am 17 May 2022
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How fast was it going when it hit the truck?
 
Tinine
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Posted: 07:29am 17 May 2022
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  PeterB said  How fast was it going when it hit the truck?
   

It spent a few days in an actual machine, to prove-out. Didn't trust the headers and so got carried away with the hot-glue gun.  
Edited 2022-05-17 17:32 by Tinine
 
Volhout
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Joined: 05/03/2018
Location: Netherlands
Posts: 3510
Posted: 07:39am 17 May 2022
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@Tinine,

The circuit I proposed uses -12V to bias the output to 0.
If you have a noisy -12V, you could inject noise.

If you use a picomite, do you use a linear regulator? or the noisy switcher ?
If you use a linear regulator, I could redesign the circuit to use the "clean" 3.3V to bias the output to 0.

AC coupling is also an option. That removes the need for biasing. The DC is created from the dutycycle, so AC coupling also gives DC stability of the loop. The only problem is that you have a huge "startup" artifact (that may also happen during a "reboot"). Not sure if this is worse than what you are trying to fix.

Let me know if you want me to spend time on it.

Regards,

Volhout
Edited 2022-05-17 17:45 by Volhout
PicomiteVGA PETSCII ROBOTS
 
Tinine
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Joined: 30/03/2016
Location: United Kingdom
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Posted: 08:08am 17 May 2022
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  Volhout said  @Tinine,

The circuit I proposed uses -12V to bias the output to 0.
If you have a noisy -12V, you could inject noise.

If you use a picomite, do you use a linear regulator? or the noisy switcher ?
If you use a linear regulator, I could redesign the circuit to use the "clean" 3.3V to bias the output to 0.

AC coupling is also an option. That removes the need for biasing. The DC is created from the dutycycle, so AC coupling also gives DC stability of the loop. The only problem is that you have a huge "startup" artifact (that may also happen during a "reboot"). Not sure if this is worse than what you are trying to fix.

Let me know if you want me to spend time on it.

Regards,

Volhout


Many thanks but I'm not worried at this stage.
When all is said and done, in a live closed-loop scenario, this analogue signal is all over the place because the output of the PID filter constantly fluctuates.
The signal feeds a 12-bit ADC that has filtering with the sampling and finally, at the end of the line, there is an electric motor.
I have a machine sitting-here, waiting for its new control system...and I'm building the control system. All of the motor-control is being handled by the 8-core Propeller and I have 4 Picomites handling the slower stuff.

This is a 6-axis CNC controller and it just so happens that 3 of the axes are tightly controlled/coordinated but the others...not so much.
Right now I'm thinking; 3 DACs of one design and 3 DACs of another design and let's see if one is better than the other when on a real machine.  


Craig

Edit:
  Quote  The only problem is that you have a huge "startup" artifact (that may also happen during a "reboot").


This would never be a problem because none of the high-power stuff is enabled until the controller is in a ready-state.
Edited 2022-05-17 18:13 by Tinine
 
phil99

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Joined: 11/02/2018
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Posted: 08:10am 17 May 2022
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To minimize the "startup artifact" is it practical for the Pico to get it's 3.3V from +1.65V and -1.65V rails? It might require opto-isolators on the inputs.
 
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