Soft-start for AC motor with an Attiny85?

[Zero999]

Zero crossing just means it only switches when the AC waveform is near zero. It can be used for PWM of a heater to control the temperature. Non-zero crossing can be used for phase control, which can be used to dim an incandescent lamp.

Here are a couple of waveforms showing the difference.

[Benta]

Umm... I think you should point out the different timebases on your plots. Otherwise they are highly confusing.
A tip: don't combine two plots in this way.

[Chriss]

I understood that zero crossing thing.
Thank you.

Im thinking about software part and uC.
To built this project. It is interesting for me. :-)

I will use a small 220/12v transformer for testing.
Is it advisable to detect the zero crossing moment with an uC interrupt i/o pin?
Or is it better to use a timer and check the state of the i/o pin let's say every 10uS or so?
I think there could also be noisy signals and if the signal is feed into an interrupt pin that could do very nasti things .

[Benta]

I understand your interest, but:
this motor is not suited for soft-starting.

[Chriss]

This project getting a new dimension.
I don't care anymore about the pump motor of my friend, I'm interested in learning and get new experience with this. I found this exciting to make this project alive. 😃

[Zero999]

Umm... I think you should point out the different timebases on your plots. Otherwise they are highly confusing.
A tip: don't combine two plots in this way.

How would you suggest I go about showing the difference? If I use the same scale, it's difficult to see the phase control waveform.

I understood that zero crossing thing.
Thank you.

Im thinking about software part and uC.
To built this project. It is interesting for me. :-)

I will use a small 220/12v transformer for testing.
Is it advisable to detect the zero crossing moment with an uC interrupt i/o pin?
Or is it better to use a timer and check the state of the i/o pin let's say every 10uS or so?
I think there could also be noisy signals and if the signal is feed into an interrupt pin that could do very nasti things .

If you use an opto-isolator with built-in zero crossing, then it's not needed. Ideally the microcontroller circuit should be powered of an isolated 5V supply, because it will make testing and debugging the circuit much easier and safer.

It's possible to use a capacitive power supply to power the microcontroller, then no opto-isolator is required and the MCU can do the zero crossing. This does work out cheaper, but it means the whole circuit needs to be treated with the same precautions as mains.

[Chriss]

I don't understand what you mean "if I use zero crossing opto, then I don't need.".
What is I don't have to need?

Bytw. I will everything separate, isolate from the mains so I always stay on the safe side.

With the 220/12V transformer I mean to use itduring the testin and building up the project.
This transformer will be powered through a 220/220V isolation transformer.
Just to be safe.

[Zero999]

I don't understand what you mean "if I use zero crossing opto, then I don't need.".
What is I don't have to need?

If you use a zero crossing opto-isolator, it will do the zero crossing for you, so there's no need to worry about coding it in the MCU.

Bytw. I will everything separate, isolate from the mains so I always stay on the safe side.

With the 220/12V transformer I mean to use itduring the testin and building up the project.
This transformer will be powered through a 220/220V isolation transformer.
Just to be safe.

Just for educational purposes, it's possible to power the MCU off a capacitive power supply.

Here's an example. Connect the zero label in the schematic to an IO pin. Program the MCU to trigger the MCU for 2ms just after zero has gone high or low, which is when the mains goes through the zero crossing point.

[Benta]

Umm... I think you should point out the different timebases on your plots. Otherwise they are highly confusing.
A tip: don't combine two plots in this way.

How would you suggest I go about showing the difference? If I use the same scale, it's difficult to see the phase control waveform.

How about just posting the plots as two images instead of one photoshopped image? Plus a comment for each? That would be a start.
I know that visualizing is not easy, I've been working with that most of my life. But always think about the recipient.
Even though I know about phase-angle and on/off AC control, it took me a bit of time to decode the time scales. Not everyone has a 12800 x 8000 screen.

[Benta]

Just for educational purposes, it's possible to power the MCU off a capacitive power supply.

Here's an example. Connect the zero label in the schematic to an IO pin. Program the MCU to trigger the MCU for 2ms just after zero has gone high or low, which is when the mains goes through the zero crossing point.

@Zero999, have you gone mad?
That circuit is lethal. You might a well say "stick your left and your right index fingers into a mains receptacle."

I'm out of this thread.

[Zero999]

Umm... I think you should point out the different timebases on your plots. Otherwise they are highly confusing.
A tip: don't combine two plots in this way.

How would you suggest I go about showing the difference? If I use the same scale, it's difficult to see the phase control waveform.

How about just posting the plots as two images instead of one photoshopped image? Plus a comment for each? That would be a start.
I know that visualizing is not easy, I've been working with that most of my life. But always think about the recipient.
Even though I know about phase-angle and on/off AC control, it took me a bit of time to decode the time scales. Not everyone has a 12800 x 8000 screen.

Okay, next time I'll post them as two images. I only have a standard HD display by the way.

Just for educational purposes, it's possible to power the MCU off a capacitive power supply.

Here's an example. Connect the zero label in the schematic to an IO pin. Program the MCU to trigger the MCU for 2ms just after zero has gone high or low, which is when the mains goes through the zero crossing point.

@Zero999, have you gone mad?
That circuit is lethal. You might a well say "stick your left and your right index fingers into a mains receptacle."

I'm out of this thread.

No, the circuit is perfectly safe, when properly constructed in accordance with the regulations. Treat the entire circuit, along with everything connected to it, with the same precautions as the mains and all will be be well.

[pcprogrammer]

As long as the other electronics like the mcu are connected to the 5V and ground of this circuit

[Zero999]

As long as the other electronics like the mcu are connected to the 5V and ground of this circuit

Yes, the MCU should be connected between +5V and ground. Obviously the ground symbol on my schematic is just the common for the MCU circuit, not actual safety ground/earth.

I don't know why people panic when they see this sort of circuit. It's fair enough to point out the hazards, but it's perfectly safe if build properly. The original poster is already talking about using an isolation transformer, which is a good thing.

If the polarity of the mains is known, then +5V should be connected to the mains neutral, rather than phase. Obviously this should still be treated the same as live, because broken neutrals aren't unheard of, but it will make it slightly safer.

[Chriss]

Thank you guys for so much valuable infos, I really appreciate it and you helped me really.

I would go back to the post #14 to the this video from YT :
https://youtu.be/HzSlUDdiTSc

I have two questions:
1. The owner of the video put two resistors in parallel R1 and R2, for what is this any good there?
I mean, one resistor is enough to limit the current for the LED.

2. In the video, he is talking about the "firing angle", ok, that is the triac G signal.
If I understand correctly how it is working:
Practically the half wave in 50Hz is 10ms long.
The G signal starts for the 10th ms and is counting backward and is triggering the G in this way:
1. trigger in 10th ms
2. trigger in 9th ms
3. trigger ins 8 ms ... etc. to 1st. ms
and the cycle is starting again.

If this is as I understand, how long could be the High time of triggering signal,
which is represented on the oscilloscope on "Chanel C" ?

Thank you.