Pwm on other port

hobby · Joined: 12 Apr 2004 Posts: 109 Location: Brussels

Hi,

It's possible to create pwm on other port (pin) ?

Small explain for what:
I needed the dimming 18 leds, the value of dimming is same for all led, but i needed the change in real time.
Only one led is light in same time, every few second the led change.

Thanks to reply
Olivier

AdrianJ · Joined: 16 Jan 2006 Posts: 2483 Location: Queensland

Doing a search for "pwm led" on the Bascom-AVR forum produces at least 26 results for this, many of which are relevant and worth reading for ideas.

hobby · Joined: 12 Apr 2004 Posts: 109 Location: Brussels

Hi,

Thanks to reply.

Not solution for me on forum.
But i found chip for this fonction: PCA9685

I publish the example of use: http://www.mcselec.com/index2.php?option=com_forum&Itemid=59&page=viewtopic&p=51187#51187

Thanks
Olivier

hgrueneis · Joined: 04 Apr 2009 Posts: 902 Location: A-4786 Brunnenthal

There is really no need for a separate chip.
Depending on the pwm frequency select a timer with the right prescale and max. count.
On timer start set or reset all led-port-pins(depending on the connection ...polarity of the leds).
For each "led on count" you can use a variable.
Then either with CASE or IF compare to the timer and if there is a timer > var. match...turn the pin off.
At a certain max. value, depending on desired frequency, restart the timer.
Just make sure that the current thru all of the leds (on at the same time) does not exceed the max. allowed current for the chip (electrical char.) mostly 200 mA.
Done
Hubert

MWS · Joined: 22 Aug 2009 Posts: 2262

Hubert,

hobby · Joined: 12 Apr 2004 Posts: 109 Location: Brussels

Hi,

thanks for your response.

I have try this solution, but is not easy (for me, i am not king of MCU), my problem is i needed the generate wait between each led.
For this solution i needed 'big' MCU (16 Output). The price of PCA + tiny 2K, is the same and i can drive more curent with PCA.

Best Regadrs
Olivier

Luciano · Joined: 29 Nov 2004 Posts: 3149 Location: Italy

"Only one led is light in same time"

If your device is a low cost toy and your LEDs can take
a reverse voltage of 5V, all you will need is one PWM
output pin and 18 pins configured as output.

1 AVR chip.
18 LEDs.
1 resistor of 470 ohm.

The PWM output will have the 470 ohm resistor connected
to it and at the other end of the resistor will be connected
the 18 anodes (+) of the LEDs. Connect the each cathode (-)
of the LEDs to an individual pin of the AVR chip configured as
output. To turn off the LED set its output to "1". To turn on
the LED set its output to "0".

Never tested, but it should work.

Best regards,

Luciano

Ken_K · Joined: 27 Jul 2008 Posts: 7 Location: Adelaide

Idea: If only one led is on at any one time you could you could connect each of the LED anodes with its resistor to a separate output pin, all the cathodes could be joined together and attached to a single PWM output pin, when any LED anode pin is high (DC 5V) its led will light at the current determined by the pwm, all OFF leds will be reverse biased. Only one PWM output required, simply switch LEDs on and off.

Note: make certain the LEDs will stand 5 volts reverse bias, else fit diodes. It may suit better to have the PWM pin on all the anodes with resistors on the cathodes, a low on the LED cathode will turn it's LED ON.

Ken

MAK3 · Joined: 24 Sep 2010 Posts: 449 Location: Germany

Hi hobby,

why don't you use an ATXMEGA for that task ?

You can configure as many output channels as output compare register are available on the XMEGA.
For example an ATXMEGA128A1 provide 24 output compare channels or an ATXMEGA64D3 come with 18 output compare channels.

See also here: http://www.mcselec.com/index.php?option=com_content&task=view&id=306&Itemid=57

This is a one chip solution (beside the LED drivers).

MAK3

MWS · Joined: 22 Aug 2009 Posts: 2262

MAK3 · Joined: 24 Sep 2010 Posts: 449 Location: Germany

Hi MWS,

hobby is already using an ATMGEA324P in his posted example (a 44-pin Chip).
I can't see that he is using a ATTINY for that in his example.
The PCA9685 only provide 16 Channels so he nee two of this additional Chip to meet the 18 PWM's.

And my proposed ATXMEGA64D3 is a 64-Pin chip.

(I only checked at Farnell but the ATXMEGA64D3 is cheapter than ATMEGA324P there)

And single slope PWM on ATXMEGA is really easy with Bascom-AVR.
Mark have done a great job to make ATXMEGA programming that easy.

MAK3

hobby · Joined: 12 Apr 2004 Posts: 109 Location: Brussels

Hi,

The specification is change, sorry 2 LEDs in same time.

Thanks
Olivier

hobby · Joined: 12 Apr 2004 Posts: 109 Location: Brussels

Hi Mak3,

Because the ATXMEGA128A1 is not low cost.
Farnell: 8Euro/10pc

With my final solution: PCA9685 2.13/10PC + ATTINT44 1.48/10pc = 3.61 Euro.

Thanks
Olivier

hobby · Joined: 12 Apr 2004 Posts: 109 Location: Brussels

Sorry,

The specification change only 16 channels.

Thanks
Olivier

MWS · Joined: 22 Aug 2009 Posts: 2262

MAK,