@Kiste (Got it ;-) )
Clever way to do it ! I guess it took some time to figure that out, and
get it running properly, specially if you further had to manage the LED
multiplexing.
Hats off !
I guess the PIC is running at a fairly high speed to be able to achieve all
that process ?
BTW: My nickname "Pinhead" is usually a term referring to a pinball freak
(which I am). Furthermore, I like horror movies, and Pinhead is the name
of one of those bad guys we love to hate (in the Hellraiser franchise).
That's why ;-)
@Rob
The resolution is not critical for dimming LED's in the way I intend: 127
steps, as in your solution, are enough. But why limit it with STEP_BRIGHT
= 2 ?
If, for example, I would like to use the ADC value of a LDR to set the
duty_cycle, I'd simply use the 8 MSB's of the ADC value, and that would
give me 8 bits resolution...
What was the requirement in your application to limit the resolution to 128
steps ?
Also, is the PWM frequency critical ? Otherwise, maybe you could get rid
of the "pwm_period = PWM_PERIOD_TIME" line, isn't it ?
All in all, those two answers are food for thoughts, and I will certainly
take your good advices. Thanks for that !
Le mercredi 21 juin 2023 à 07:59:57 UTC+2, Rob CJ a écrit :
> Hi David, Oliver,
>
> What should be the resolution of the PWM? I sometimes made it in software
> using one timer and controlling several LEDS. In the example below I
> control one LED using 128 steps (step increment of 2 (STEP_BRIGHT)) but can
> be extended with more LEDs. Would that be sufficient for your application?
>
> This was running on a 12F675 running at 4 MHz. The refresh rate was about
> 80 Hz to prevent flicker. Below this program you find some calculations.
> Normally I used Timer 2 because of the automatic reload but this PIC did
> not have that.
>
> ; Interrupt routine for timer 0, handling the PWM signal in software.
> ; This routine is called every 107 us (measured) and takes between 18-28
> us.
> procedure timer_0_interrupt() is pragma interrupt
>
> if INTCON_T0IF then
>
> ; First preset the time for the next interrupt.
> TMR0 = TIMER_0_RELOAD
> INTCON_T0IF = FALSE
>
> ; Check the if we need to start a new period.
> if (pwm_period == 0) then
> ; New period. Switch LEDs on and start a new duty cycle.
> pwm_period = PWM_PERIOD_TIME
> pwm_timer = duty_cycle
> ; Only turn LED on if it has a duty cycle to prevent flashing.
> if (pwm_timer > 0) then
> LED = LED_ON
> end if
> else
> pwm_period = pwm_period - 1
> end if
>
> ; If the timer of the LED is at the mininum brightness then time
> has passed.
> if (pwm_timer >= BRIGHT_MIN) then
> pwm_timer = pwm_timer - STEP_BRIGHT
> else
> LED = LED_OFF
> end if
>
>
> end if
>
> end procedure
>
> Some constants I used.
>
> ; Specify the values for the minimum and maximum brightness of the LEDs and
> ; the value to increase or decrease it. The minimum value is not zero since
> ; we want to know if the device is on or off so there always has to be a
> ; minium brightness when the device is switched on.
> const byte BRIGHT_MIN = 10 ; Must be >= STEP_BRIGHT.
> const byte BRIGHT_MAX = 254 ; Must be even and <= 254
> const byte STEP_BRIGHT = 2 ; This gives 254 / 2 = 127 steps.
>
> ; Timer reload value. The clock is 4 MHz so the timer clock is 1 MHz. Let's
> ; use 80 Hz as PWM frequency for the LEDs. This means that the timer has to
> ; run at 80 * 125 steps = 10.000 Hz or a period time of 100 us. With a
> prescale
> ; of 2 (minimum) the we need a timer value of 1.000.000 / 2 / 10.000 = 50.
> ; Since we use the timer overflow the reload value becomes 256 - 50 = 206.
> ; The measured value is 9.333 Hz, most like due to processing time.
> const byte TIMER_0_RELOAD = 206.
>
> ; See timer init, 10.000 Hz / 125 gives 80 Hz. Measured is 74 Hz.
> const byte PWM_PERIOD_TIME = 125
>
> Kind regards,
>
> Rob
>
> ------------------------------
> *Van:* 'Oliver Seitz' via jallib <jal...@googlegroups.com>
> *Verzonden:* woensdag 21 juni 2023 07:38
> *Aan:* jal...@googlegroups.com <jal...@googlegroups.com>
> *Onderwerp:* Re: [jallib] Software PWM
>
> Salut pinhead,
>
> If I had to extend an existing controller with PWMs, I'd use e.g.
> PIC16F18313. It has 8 pins, I2C and 4 independent PWMs at a cost of less
> than 1,50€. I cannot tell however if the MCLR pin can be used for I2C. A
> safe choice would be 12F1572 which is even cheaper and has 4x 16bit PWM.
> You can use serial_software for communication, as the PWMs run happily on
> their own.
>
> Yes, the way you're describing you could dim LEDs, but each time something
> else is happening, like new I2C-input is processed, all your LEDs would
> slightly flicker.
>
> When I did bitbang-dim 120 multiplexed LEDs, i did it binarily: If bit 7
> is set, light up the LED for 128µs. Then, if bit 6 is set, light up the LED
> for another 64µs and so on. The brightness sums up in the eye of the
> beholder. I've programmed a timer to generate an interrupt in succession
> after 128, then 64, then 32... µs. However, 4,2 and 1 µs I did without
> leaving the ISR. I did not use any "if" for that, I had an 8x8bit matrix
> with the dimming values, which I rotated by 90°, so I had a byte full of
> "bit7" of each channel, a "bit6" of each channel and so on. So, the ISR had
> nothing to do but move the "bit7"-byte to the output port right before the
> 128µs interrupt delay, the "bit6"-byte before the 64µs delay... That way I
> could dim 8 LEDs (all on e.g. PORTA) for the price of one.
>
> Oliver is my real name, but Kiste (=Carton(fr) =Doos(nl) =Box(en)) is my
> very common nickname, even in real life.
>
> Greets,
> Kiste
>
> Am Dienstag, 20. Juni 2023 um 22:10:07 MESZ hat pinhe...@gmail.com <
> pinhe...@gmail.com> Folgendes geschrieben:
>
>
> Hello Oliver,
>
> Indeed, PIC18F27J13 could be a candidate. I overlooked this one too
> quickly (I already ranted about the parametric search tool on the µchip
> site :-{ )
> I'll check for the other characteristics.
> No internal OPAMP and internal VREF are a bit annoying, but if it's the
> only missing parts, it's ok.
>
> Anyway, what about a PIC that would be programmed as a I²C generator with
> several independant channels, and I²C slave.
>
> He would have nothing else to do than generating the signals.
> Consider one channel:
> - A register contains the value of its duty cycle (from 0 to 255)
> - In the main loop, a 8-bit counter is incremented.
> - At each increment, its value is compared to the duty cycle register,
> and if needed, the corresponding output is toggled.
>
> You could generate as many PWM signals as there are IOs available.
> The I²C-slave interface would be handled by the MSSP module with
> interrupts (yes, this could cause glitches in the PWM signals if the time
> needed to process the I²C processes is greater than the time it takes to
> increment the PWM counter by one, but if it is only to dim some LED's, I
> think I could live with it)
> The frequency could be adjusted by changing the oscillator frequency
> and/or adding delays in the main loop when the main counter is incremented
>
> Just for the sake of it, I think I will give it a try.....
>
> Hoping I am not overlooking a major impediment
>
> Thanks for your suggestion, Oliver (or Kiste ?)
>
>
> Le mardi 20 juin 2023 à 20:43:01 UTC+2, Oliver Seitz a écrit :
>
> Hi!
>
> A software PWM library isn't easy. Without a timer, it blocks everything.
> With a timer, it's complicated and would only add a few channels. I've done
> software PWM for 120 LEDs independently with a 28 pin controller, but it
> couldn't do much more than that at 64MHz.
>
> Have you had a look at, say, PIC18F27J13? It has 3+7 independent ccp
> modules (with 3 TMR2-type timers).
>
> Greets,
> Kiste
>
> Am Dienstag, 20. Juni 2023 um 19:49:33 MESZ hat pinhe...@gmail.com <
> pinhe...@gmail.com> Folgendes geschrieben:
>
>
> Hi,
>
> I'm falling short of PWM outputs for a project.
> I need 6 independant outputs, and the only way to get them is to use a
> 64-pin 18fxxxx, which is a bit overkill for me, or use a second PIC, bond
> to the first (I²C or SPI) which is also overkill but could be acceptable in
> the absence of another "clean" solution.
>
> It will only be used for dimming LED's, and I don't need particular
> features like dead-band, half or full bridges, precise or stable
> frequency.....
>
> To my surprise, I didn't find a software PWM library in Jallib 1.8.....
> Or do I miss something ?
>
> Have a nice day
>
>
>
>
>
>
> --
> You received this message because you are subscribed to the Google Groups
> "jallib" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to jallib+un...@googlegroups.com.
>
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/jallib/923bd215-4855-49d9-b7e1-17e02482c219n%40googlegroups.com
>
> <https://groups.google.com/d/msgid/jallib/923bd215-4855-49d9-b7e1-17e02482c219n%40googlegroups.com?utm_medium=email&utm_source=footer>
> .
>
> --
> You received this message because you are subscribed to the Google Groups
> "jallib" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to jallib+un...@googlegroups.com.
> To view this discussion on the web visit
>
> https://groups.google.com/d/msgid/jallib/9aad71fb-a1f2-47f3-8cc4-82a1110327c2n%40googlegroups.com
>
> <https://groups.google.com/d/msgid/jallib/9aad71fb-a1f2-47f3-8cc4-82a1110327c2n%40googlegroups.com?utm_medium=email&utm_source=footer>
>
> .
>
> --
> You received this message because you are subscribed to the Google Groups
> "jallib" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to jallib+un...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/jallib/1639372286.1548147.1687325901648%40mail.yahoo.com
>
> <https://groups.google.com/d/msgid/jallib/1639372286.1548147.1687325901648%40mail.yahoo.com?utm_medium=email&utm_source=footer>
> .
>
--
You received this message because you are subscribed to the Google Groups
"jallib" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to jallib+unsubscr...@googlegroups.com.
To view this discussion on the web visit
https://groups.google.com/d/msgid/jallib/87f34955-bd10-4bca-980b-8cce7b5dac0an%40googlegroups.com.
