Pwm circuit trouble

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lschiavo

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I built this circuit. 9V wall wart supply. Tried an extra filter cap.



It tested fine originally. Now with it hooked up to the SSR, It gets hung up on the extremes of the pot settings - not getting triggered. It works fine in the mid range and nearly to the extremes. F=0.64. I was thinking of just upping the 1k's to 4.7k. Anyone see an obvious problem here?
 

Walker

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When you say "not getting triggered" do you mean that the SSR is not being driven when you set the duty cycle very low or very high?
 

Walker

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One other question: how hard is it to disassemble this? Did you solder it all down, or are you using a solderless breadboard.

The reason I ask is because you can re-wire this and get the PWM built with out any resistors (other than the pot) and drop one of the diodes.

Having the fixed 1k resistors in there means you don't have a full range of control. There is ALWAYS some resistance on the charge and discharge path, so you won't be able to get to 0% or 100%, but it might be close enough that you can't notice.

With the resistor-less, 2-diode circuit that I use, I can get a full 0%-100% adjustment.
 
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lschiavo

lschiavo

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Walker said:
When you say "not getting triggered" do you mean that the SSR is not being driven when you set the duty cycle very low or very high?
No. The 555 circuit sticks off. I was just looking at it. It seems to be only on the Max side. If I crank it up it will time out one cycle and just stay off.
 
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lschiavo

lschiavo

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Walker said:
One other question: how hard is it to disassemble this? Did you solder it all down, or are you using a solderless breadboard.

The reason I ask is because you can re-wire this and get the PWM built with out any resistors (other than the pot) and drop one of the diodes.

Having the fixed 1k resistors in there means you don't have a full range of control. There is ALWAYS some resistance on the charge and discharge path, so you won't be able to get to 0% or 100%, but it might be close enough that you can't notice.

With the resistor-less, 2-diode circuit that I use, I can get a full 0%-100% adjustment.
Full on/off would be cool. Do you have a schematic? I will build another. Max pot I have is 100k though.
 

Walker

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I am not saying that your citcuit is responsible for the behavior you are getting, so keep that in mind. something else is going on at the high end.

anyway, here is the schematic for what I use:
 
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lschiavo

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Walker said:
I am not saying that your citcuit is responsible for the behavior you are getting, so keep that in mind. something else is going on at the high end.

anyway, here is the schematic for what I use:
Something is funny with my circuit. I am going to try to figure it out for curiosities sake.

I like your circuit much better. I will just build a new one. It will be worth it for full on/off. Thanks for the help.
 
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lschiavo

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It was a bad pot. I built your circuit anyway. It did the same thing with the old pot. I get the slightest flash when set to off. Is this normal? Maybe all my pots are just old.

Thanks again for the help Walker.
 

Walker

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It was a bad pot. I built your circuit anyway. It did the same thing with the old pot. I get the slightest flash when set to off. Is this normal? Maybe all my pots are just old.

Thanks again for the help Walker.
I *sometimes* see the light illuminate in the 0% setting, but not even enough to really light up. It has to be really dark in the garage for me to even notice it.

And it doesn't last long enough for the SSR to react to it. The switching time of the SSR is longer than that faint pulse, so no heating happens.
 
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lschiavo

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Okay. I will call it a success then. The controller is done!

This is actually for Yooper. Now I need to work on my panel because hers is better.
 

Walker

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Okay. I will call it a success then. The controller is done!

This is actually for Yooper. Now I need to work on my panel because hers is better.
Oh... if this is for Yooper, then I am going to send her a paypal invoice for my consulting fees.
 

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Walker,

Any idea on how to hook this circuit up to a dalsemi DS1805?

TIA.

EDIT: never mind. The DS1805 seems to be mostly unavailable. DigiKey has a few 10k's but that's it. Jameco & Allied don't even list them.


I am not saying that your citcuit is responsible for the behavior you are getting, so keep that in mind. something else is going on at the high end.

anyway, here is the schematic for what I use:
 
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