PWM not go to zero

Log in or register to post comments
Go To Last Post
18 posts / 0 new
Author
Message
zettaman
zettaman's picture
Level: Hangaround
Joined: Sat. Feb 21, 2009
Posts: 133 View posts
Location: Island of mediteranean sea
#1
Posted by zettaman: Sat. Feb 12, 2011 - 06:08 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hello

I'm using pwm with led.

When i put zero to OCR0A (for instance) the led don't go down : there is a few light...

Somebody have an idea?

Notice that the led is connected direct to avr (with a R).

Thanks

computer : GNU Linux / e6750
ship : Attiny 2313 / ATmega8
compiler : avr-gcc 1:4.3.2-1

Tags:

AVR Microcontrollers, megaAVR and tinyAVR
Top
Gold Markclawson
clawson's picture
Level: Moderator
Joined: Mon. Jul 18, 2005
Posts: 102097 View posts
Location: (using avr-gcc in) Finchingfield, Essex, England
Posted by clawson: Sat. Feb 12, 2011 - 06:27 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I think the usual suggestion is to use the COM bits to complement the PWM output then set OCR0A to the maximum value.

Top
zettaman
zettaman's picture
Level: Hangaround
Joined: Sat. Feb 21, 2009
Posts: 133 View posts
Location: Island of mediteranean sea
Posted by zettaman: Sat. Feb 12, 2011 - 06:50 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Oh, Clawson, still the first to answer...

Thanks, i will try this.

computer : GNU Linux / e6750
ship : Attiny 2313 / ATmega8
compiler : avr-gcc 1:4.3.2-1

Top
zettaman
zettaman's picture
Level: Hangaround
Joined: Sat. Feb 21, 2009
Posts: 133 View posts
Location: Island of mediteranean sea
Posted by zettaman: Thu. Mar 10, 2011 - 07:45 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Ok it's efficient (sorry for my english)
With ocrx=255 : no light.

But i don't understad why...

Could you explain...
This problem come with 8bit counter (counter0 of attiny2313)
No problem with the other counter...

computer : GNU Linux / e6750
ship : Attiny 2313 / ATmega8
compiler : avr-gcc 1:4.3.2-1

Top
hardwarehank
hardwarehank's picture
Level: Rookie
Joined: Sat. Feb 19, 2011
Posts: 36 View posts
Location: Maryland
Posted by hardwarehank: Thu. Mar 10, 2011 - 08:35 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Here's an example of PWM on the ATtiny85. I'm sure you could adapt it to the 2313.

Mistakes I've made

  • Not copying the .data section to hex using avr-objcopy
  • Overflowing RAM in an ATtiny2313 (128 Bytes)

Top
Bronze Marktheusch
theusch's picture
Level: 10k+ Postman
Joined: Mon. Feb 19, 2001
Posts: 40151 View posts
Location: Wisconsin USA
Posted by theusch: Thu. Mar 10, 2011 - 08:40 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Quote:

Could you explain...
This problem come with 8bit counter (counter0 of attiny2313)
No problem with the other counter...

Then you need to show us the setup for both.

If you are using the full range of the counter, the 8-bit counter will be high 1 of 256 counts--about 1/2% You get some light. On the 16-bit, 1/65536 or about 0.0015%. You can't see that light.

Quote:

But i don't understad why...

What part don't you understand? have you looked at the signals with an oscilloscope?

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Top
John_A_Brown
John_A_Brown's picture
Level: Raving Lunatic
Joined: Sat. Sep 20, 2003
Posts: 6196 View posts
Location: Underneath the Cotswolds escarpment, England.
Posted by John_A_Brown: Fri. Mar 11, 2011 - 12:41 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I'm pretty certain that the data sheet explains that OCR = 0 will actually still give a pulse of one counter clock, which, as The Usch explained, will still be visible using 8 bit PWM.

You can, of course, trap the zero condition and set the output pin for normal operation in this case.
However, Cliff's solution of inverting the sense is probably easier.

Four legs good, two legs bad, three legs stable.

Top
zettaman
zettaman's picture
Level: Hangaround
Joined: Sat. Feb 21, 2009
Posts: 133 View posts
Location: Island of mediteranean sea
Posted by zettaman: Fri. Dec 7, 2012 - 11:05 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

thanks...

computer : GNU Linux / e6750
ship : Attiny 2313 / ATmega8
compiler : avr-gcc 1:4.3.2-1

Top
Be_logic
Be_logic's picture
Level: Wannabe
Joined: Sun. Mar 4, 2018
Posts: 54 View posts
Posted by Be_logic: Mon. Oct 8, 2018 - 10:51 AM (Reply to #5)
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

could I use this principle at the and of your example for getting PWM to 0 when the AD convertion is at the lowest level in my source?

 

regards,

Bert

Top
Bronze Marktheusch
theusch's picture
Level: 10k+ Postman
Joined: Mon. Feb 19, 2001
Posts: 40151 View posts
Location: Wisconsin USA
Posted by theusch: Mon. Oct 8, 2018 - 02:33 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Be_logic wrote:
could I use this principle at the and of your example for getting PWM to 0 when the AD convertion is at the lowest level in my source?

Sigh--I see another request; I answered in that thread as well as above.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Top
Be_logic
Be_logic's picture
Level: Wannabe
Joined: Sun. Mar 4, 2018
Posts: 54 View posts
Posted by Be_logic: Tue. Oct 9, 2018 - 12:31 PM (Reply to #10)
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

sigh, I can ask questions where I like I think?

Top
Bronze Markjs
js's picture
Level: Moderator
Joined: Wed. Mar 28, 2001
Posts: 30277 View posts
Location: Sydney, Australia (Gum trees, Koalas and Kangaroos, No Edelweis, but plenty of Corona beer)
Posted by js: Tue. Oct 9, 2018 - 08:12 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I can ask questions where I like I think?

Not necessarily, if the topic is repeated the thread gets locked. Anyway your question in 9 was to a thread that has been unused for 6/7 years and unlikely to get a reply from the OP.

John Samperi

Ampertronics Pty. Ltd.

https://www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

Top
Bronze Marktheusch
theusch's picture
Level: 10k+ Postman
Joined: Mon. Feb 19, 2001
Posts: 40151 View posts
Location: Wisconsin USA
Posted by theusch: Tue. Oct 9, 2018 - 08:18 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 1

js wrote:
Anyway your question in 9 was to a thread that has been unused for 6/7 years and unlikely to get a reply from the OP.

What is interesting, John, as I mentioned it is probably the same situation.  And OP did dig out the related thread.  The "sigh" is that in both this thread and the other one the probable solution was outlined -- inverted PWM.  Yet Be_logic seems to want more. 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Top
avr-mike
avr-mike's picture
Level: Resident
Joined: Sat. Jul 21, 2018
Posts: 865 View posts
Location: U.S. Pacific
Posted by avr-mike: Tue. Oct 9, 2018 - 08:30 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 1

Well, there is the method mentioned in #7 that Arduino uses -- if you set the

"Analog" output to 0 it disables the timer pin and sets the PORT bit to 0.

 

--Mike

 

Top
Be_logic
Be_logic's picture
Level: Wannabe
Joined: Sun. Mar 4, 2018
Posts: 54 View posts
Posted by Be_logic: Wed. Oct 10, 2018 - 01:26 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi, hopefully the code snippit is enough so when I change adc = ADC_MIN; into adc=0, lowest PWM value is the same, so not zero.

Where can I find an example about #7 trapping the zero condition.

 

The trouble is that the potentiometer on de AD input has a lowest value of 60 Ohm and at that lowest position PWM should be zero.

 

Sorry I could not send the code snippit with <> because I don't know how to use it.

e.g. It's impossible to paste in the window that opens after klicking <>

 

regards,

Bert

 

Top
Bronze Marktheusch
theusch's picture
Level: 10k+ Postman
Joined: Mon. Feb 19, 2001
Posts: 40151 View posts
Location: Wisconsin USA
Posted by theusch: Wed. Oct 10, 2018 - 01:37 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

You were told in this thread and the other one how to do it -- use inverted PWM.  I'd guess it has been brought up many times.  It was also explained why it happens.  Yes, if you care to you can turn the timer/PWM off and on.  Often/usually it is simpler just to use inverted PWM if there is no hard requirement for 100% duty.

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Top
Bronze Marktheusch
theusch's picture
Level: 10k+ Postman
Joined: Mon. Feb 19, 2001
Posts: 40151 View posts
Location: Wisconsin USA
Posted by theusch: Wed. Oct 10, 2018 - 01:43 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

theusch wrote:
I'd guess it has been brought up many times.

https://www.avrfreaks.net/forum/... with a datasheet quote

https://www.avrfreaks.net/forum/... with links to prior

https://www.avrfreaks.net/forum/...

https://www.avrfreaks.net/forum/... see title -- applicable?

https://www.avrfreaks.net/forum/... good explanation in #6

...

 

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

Top
Be_logic
Be_logic's picture
Level: Wannabe
Joined: Sun. Mar 4, 2018
Posts: 54 View posts
Posted by Be_logic: Wed. Oct 10, 2018 - 03:42 PM (Reply to #17)
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Many thanks!

 

Bert

Top