Modifying the Dimmer Circuit

You can get digital potentiometers these days, a digital input gives a resitance proportional to the data.
Try googling digital potentiometer. digial variable resistance, or digital programable resistor.
That would prob be simplest.
Del

Sounds good - but I'm not sure what's the highest voltage it would ever see - may need some protection(?). Also, optoisolation is a good idea. _(Hic).

I had that in mind, but was not sure if I could get digital potentiometer where I stay. I could use an R-2R laddder, but that would make the circuit bigger in space. But for now, I think using a digital potentiometer is the best option.

Nevertheless, which IC would you suggest for such a circuit? Would the AD8400 be a good option?

Dunno, ya gotta read the spec and make your own decision.
Del

This link may be useful to you

http://www.dv-fansler.com/Computer%20Lights/dimmers.htm

Dimming from a microcontroller is often done for computer controlled xmas lights and searches for things relating to that should give you good results. There are a few different ways of doing this, so you can decided which one works best for your use.

The more conventional approach when using a uControllers in dimming circuits is to provide a zero crossing signal to the uCont and have it control the gate on the thyristor directly.

I'm curious as to what type of light your wanting to control with your dimmer? On a previous thread, the OP was wanted a wiring "plan" for replacing a wall toggle switch with a wall mounted dimmer switch. It sounded simple enough until post #21 of that thread, that we got a hint that the OP was planning to use CFLs on the dimming circuits. Not saying that it wouldn't work, just that he wasn't aware of some of the draw backs of controlling CFLs with a dimmer switch. Another thing I'm curious about is, do you have the extra room in the switch box to allow for the extra components of a programmable dimmer? I don't know what your working with but I would venture to say, that your going to need either, an extra deep single gang box or a double gang box to allow for your programmable dimmer.

Not for the CFL.

Hi One & All,

1.) Microchip manual TB094 http://ww1.microchip.com/downloads/en/AppNotes/91094A.pdf has a very nice simple circuit using a PC chip that works as a Digital dimmer at 110V AC. I would add fuse of about 1.5A slow blows type on the A/C input. The other thing that might be a problem, You will have to write your own program but they give you a lot information to help you. Plus, you need to buy a programmer device. The programmer device usually comes with programming software.

2.) Use a Velleman-kit K8064 http://www.apogeekits.com/PDF_Files/Light_Dimmer_Manual.pdf. Plus, using a LM117 http://www.national.com/ds/LM/LM117.pdf as controlling voltage source.

3.) Onsemi Pub AND8011 http://www.onsemi.com/pub_link/Collateral/AND8011-D.PDF has nice circuit.

4.) Look at another simple circuit at http://www.electro-tech-online.com/attachments/electronic-projects-design-ideas-reviews/48250d1290173549-ac-dimmer-circuit-microcontroller-controlled-dimmer-parts.jpg

Let us know how the work out?

BEN

I don't know, it seems like a lot of work for reinventing the wheel and with more components to fail. I always liked the K-I-S-S approach.

Can anyone tell me if I used AD8400 instead of the variable resistor in the circuit shown above, will it work? My concern is using AD8400 with the mains (240 V, 50 Hz AC). I don't know if it will be able to handle.

Ok...
Out of the kindness of my feline heart, and the fact that I gave you a bum steer.
I googled AD8400 spec. The resistor terminal maximum voltadge is the VDD supply of the chip, (VDD being 2.7 to 5.5 volts max) therefore NO it's not suitable.
The point is, if you can't understand the spe's sheet of an IC you have almost zero chance of using it successfully.
I'm not having a pop at you. A while ago I tried to use a fancy battery charger IC... it was pants, even with the application notes it didn't work, (It was trying to fulfill too many functions at once, SMPSU chip, battery charger etc) so I gave up and made a simple 3 stage charger myself.
Some manufacturers have good app notes and chips which work (Maxim, NS) some have spec sheets and notes written by troops of marauding monkeys with typewriters.
Del

You have supplied the basic circuit BUT FORGOT and possibly with that in mind -- what you are trying to do -- that has generated a lot of messages that at the end are not usable by you because you do not explain IN DETAIL what you want to do

It seems that You want to do it digitally and if it is like that why don't you say it to assist those that want to assist you .

To accomplish such digital control you need to have a reference and that is the zero crossing of the sine wave feeding the triac circuit -- so the digital circuit receiving the reference point then the , I presume a microprocessor, will determine where the trigger pulse is generated to turn the TRIAC -- ON - remembering that the TRIAC turns OFF when the sine wave crosses a voltage level toward ZERO volts when the holding Current of the TRIAC is lower -- also remembering that the TRIAC has to have a certain minimum voltage above the generated holding current to stay ON for the rest of the half Hertz .

Detail what you want to do and you will get the proper assistance, I think !!

"Detail what you want to do and you will get the proper assistance, I think !!"

I want to change the duty cycle of the dimmer output using binary signals from 4 or 8 pins of the microcontroller (I am not using a microprocessor, I am using Atmega16).

Del the cat gave reason as to why I can't use the AD8400, so what is a good option here?

You are using a microprocessor it is the Atmega 16 which is an 8 bit unit.

You need to have the zero cross reference of the sine wave , know the sine wave 1/2 frequency and learn to pulse the Triac starting at around 170 degrees from zero crossing with a pulse at least 1 millisecond duration and increment the TRIAC time by regressing toward the zero crossing which give a PWM to the TRIAC, the maximum width in this case would be around from 10 degrees from Zero crossing to 170 degrees from zero crossing .

http://www.atmel.com/dyn/resources/prod_documents/doc2466.pdf

A wiser message would be to show what you want to do as a final product -- the AD8400 is totally unnecessary if you learn to use the microprocessor well.

Yes, but Atmega16 is a microcontroller why do you keep calling it a microprocessor?

A micro controller is a micro processor -- just semantics

See the block diagram of your ATMEGA 16 .