AVR-Chat

At 11:10 PM 12/10/04 -0800, you wrote:
>thanks robert, i will try it. if IR2110 can isolate 500V then i can save 
>my optocouplers..
>i have attach my first hbridge cct without using ir2110.i only need to 
>switching Q1 or Q2 but not the both at the same time.
>
>i am using bascom AVR 1.11.7.4 with AtMega8535 chip
>i use this hbridge cct to drive a single phase motor and would like to 
>switching the mosfet at accurate timing at 50Hz.

As I said unless you are driving AC 50Hz is awfully slow.

However, you still haven't answered the question:  What do you not mean by 
not getting a square wave?  What exactly are you seeing?

And now that I've seen the circuit where are you measuring it?

Personally I wouldn't use this circuit.  In particular the drive scheme on 
the low side is going to be a potential problem source.  It's vulnerable to 
inductive kickback (you are driving a motor after all).  I'd also get rid 
of the diodes, they are doing nothing for you, particularly at 50Hz.  The 
low side drive will certainly fail at higher voltages so why use it at low 
voltages?  Since you appear to be using low voltages to test and learn (a 
good idea) you learn little if you use a totally different drive scheme for 
the two cases.

>
>(1) so what commands can i use..because now i write a simple program like 
>below;
>
>Do
>    reset pina.2
>    set pina.1
>    reset pina.2
>    waitms 10
>    reset pina.1
>    set pina.2
>    waitms10
>
>loop

Three questions:  Where are you measuring the square wave?
         What does it look like (IE what do you mean by not square)?
         Do you know what duty cycle means?


>is these commands can be used for switching the mosfets. i try this on my 
>first cct,i work fine for small LSM motor(12V <1A) but it seems weak when 
>drive larger LSM motor (15V 3A),why?

What are your rise and fall times like?
What does the power rail look like?
Have you measured the current?  If so what does that waveform look like and 
how does it compare to the ideal driving waveform?

>i need to generate 2 output for now and later will modify my cct by using 
>IR2110 and need four output from my chip but 8535chip dont have four timer 
>or PWM so how....

Why?  In fact I think generating 4 separate outputs to drive the H bridges 
is possibly the worst method.  It's certainly the most likely to result in 
timing errors.  On the upside I suppose it could allow tuning the deadband 
in SW but I don't believe you have anything fast enough to do that.

At most you should need one PWM per phase (and maybe some discrete steering 
logic).

>
>after this i need to build 3phase also which need 12 output from chip to 
>switching the mosfets...

I don't see why.

>
>(2) how can i change the duty cycle? because i may use 4 output from 
>8535chip when i use IR2110..what commands can i used??

This is a bit Socratic but I think justified (especially since this is an 
educational project).

First define duty cycle.  If you don't know what that is go and read a 
little bit on PWMs and then come back.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III