Easy PWM Dimmer

Sili · Nov 5, 2013

Hi all!

i just got my 08M2 on an AXE230 Board.

Id like to use PWM for the first time. Setup is very easy. Mechanical switch at P3, LED at P2.

If the Button is pushed, the Led should start Fading in until 100% brightness are reached, pause for a second or so and then start fading out, returning to the main tab, waiting for an input.

it might be very easy, but i didnt find a tutorial which i understood

maybe someone could help me with a snippet of code.

thanks so much!

Captain Haddock · Nov 5, 2013

This is a very simple led dimmer using a 10K pot at C.1 across 0V & 5V, works fine for me.(Can't remember why I added the +3 at line 5 though)

Code:

#picaxe 08m2
main:
setfreq m8
	readadc C.1,b0;
	let w1 = b0 * 4+3
	pwmout c.2, 255, w1
debug
goto main

nick12ab · Nov 5, 2013

To create a dimming effect using PWM, you can use a for loop. The for loop needs to contain a pwmduty command that will set the duty cycle of the pwm signal that you create at the beginning of the program by using the pwmout command.

In the for loop, there is no need to have a load of if statements to determine the duty cycle; you use the counter variable that you used for the for loop.

Example code:

Code:

#picaxe 08m2

symbol pushbutton = pinC.3
symbol led = C.2
symbol counter = b4


	pwmout led,63,0
main:
	if pushbutton = 1 then
		for counter = 0 to 254
			pwmduty led,counter
			pause 10
		next
		pause 1000
		for counter = 255 to 1 step -1
			pwmduty led,counter
			pause 10
		next
	end if
	goto main

Sili · Nov 5, 2013

Hi Haddock.

Thank you for that example. i didnt use a pot for that.

i tried this one:

Code:

init:                                                                     
            symbol Counter=b0                            

main: high 2
if input3 = 0 then dim
goto main


dim:               
           For Counter = 255 to 0 step -1          
                   PWM 2, Counter, 1
                   
           Next Counter                                        
           For Counter = 0 to 255 step 1                    
                   PWM 2, Counter, 1                      
           Next counter                                        
 
	     
           goto main                                              
           End

i used a mechanical switch (n.c, thats why its set to input3=0)
is is possible to set to brightness to which it dimms down and the speed with that it is dimming to a random amount using the random command?
the target is to get an unstable (smooth) "flicker" of light

Paix · Nov 5, 2013

Welcome to the forum Sill, do you mean a flickering flame effect, like that of a candle?

Just to clarify for others.

Sili · Nov 6, 2013

Paix said:
Welcome to the forum Sill, do you mean a flickering flame effect, like that of a candle?

Just to clarify for others.

Hey Paix,

Something like that yeah. In fact im working on a new Version of a flickering light. For some Halloween Setups i use a easy Setup with a lamp starter for fluorescent lamps within a A/C Cable. With that i get an effect like this:

But what i want is a better circuit (without the starter!) which provides a better effect bad electricity. not a full shut-down of the ligh, more like a loss of voltage on the powerline.
It should look like in horrormovies, when the young girl enters the basement and suddenly the lights start so flicker before it gets dark.. maybe you know what i mean.

i think it could be the effect of an candle just a litte bit slowed down!

eclectic · Nov 6, 2013

As a little experiment,
connect your LED/resistor to input/output 2.

Then run the following program:

Code:

#picaxe 08M2

; see Manual 2 PLAY command

Main:

play 1, 0
sertxd ("1",cr,lf)

pause 1000

play 2 ,0
sertxd ("2",cr,lf)

pause 1000

Play 3,0
sertxd ("3",cr,lf)

pause 1000

Play 4, 0
sertxd ("4",cr,lf)

Pause 1000

goto main

e

Sili · Nov 6, 2013

eclectic said:
As a little experiment,
connect your LED/resistor to input/output 2.

Then run the following program:

Code:

#picaxe 08M2 ; see Manual 2 PLAY command Main: play 1, 0 sertxd ("1",cr,lf) pause 1000 play 2 ,0 sertxd ("2",cr,lf) pause 1000 Play 3,0 sertxd ("3",cr,lf) pause 1000 Play 4, 0 sertxd ("4",cr,lf) Pause 1000 goto main

e

Is it playing Silent Night and Rudolph with an LED instead of a speaker???

eclectic · Nov 6, 2013

Yes, but

does it flicker as you want it?

e

eclectic · Nov 6, 2013

Alternatively, for a "crackly bulb",
connect a Piezo in parallel to the LED/resistor.

Code:

#picaxe 08M2

pwmout C.2, 63, 63

do
random W0

pwmduty C.2, b0

loop

e

Sili · Nov 6, 2013

eclectic said:
Yes, but

does it flicker as you want it?

e

I'm still at work. Gonna test it this afternoon when im Home.
Could be a a solution. But is it dimming the LED up and down or just turning it on and off in random sequences?

eclectic · Nov 6, 2013

Sili said:
I'm still at work. Gonna test it this afternoon when im Home.
Could be a a solution. But is it dimming the LED up and down or just turning it on and off in random sequences?

See post #10, then try both methods.

e

Sili · Nov 6, 2013

eclectic said:
See post #10, then try both methods.

e

Thats crazy.

I tried that one without the piezo:

Code:

picaxe 08M2

; see Manual 2 PLAY command

Main:

play 1, 0
sertxd ("1",cr,lf)

pause 1000

play 2 ,0
sertxd ("2",cr,lf)

pause 1000

Play 3,0
sertxd ("3",cr,lf)

pause 1000

Play 4, 0
sertxd ("4",cr,lf)

Pause 1000

goto main

thats very close to what i want, but its still very "hard" (like the fluorescent lamp starters). i miss the smooth change of brightness as achieved with the pwm code

nick12ab · Nov 6, 2013

Sili said:
i used a mechanical switch (n.c, thats why its set to input3=0)
is is possible to set to brightness to which it dimms down and the speed with that it is dimming to a random amount using the random command?
the target is to get an unstable (smooth) "flicker" of light

Yes you can use the random command so that the light dims down to a random amount or at a random speed. Here is some code that is not written very well and is uncommented but it does produce a random flicker and fade effect.

Code:

[color=Navy]#picaxe [/color][color=Black]08m2[/color]

[color=Blue]symbol [/color][color=Black]pushbutton [/color][color=DarkCyan]= [/color][color=Purple]pinC.3[/color]
[color=Blue]symbol [/color][color=Black]led [/color][color=DarkCyan]= [/color][color=Blue]C.2
symbol [/color][color=Black]random1 [/color][color=DarkCyan]= [/color][color=Purple]w0[/color]
[color=Blue]symbol [/color][color=Black]random1msb [/color][color=DarkCyan]= [/color][color=Purple]b1[/color]
[color=Blue]symbol [/color][color=Black]random2 [/color][color=DarkCyan]= [/color][color=Purple]w1[/color]
[color=Blue]symbol [/color][color=Black]random2msb [/color][color=DarkCyan]= [/color][color=Purple]b3[/color]
[color=Blue]symbol [/color][color=Black]random3 [/color][color=DarkCyan]= [/color][color=Purple]w2[/color]
[color=Blue]symbol [/color][color=Black]random3msb [/color][color=DarkCyan]= [/color][color=Purple]b5[/color]
[color=Blue]symbol [/color][color=Black]counter [/color][color=DarkCyan]= [/color][color=Purple]b6[/color]
[color=Blue]symbol [/color][color=Black]tempvar1 [/color][color=DarkCyan]= [/color][color=Purple]b7[/color]
[color=Blue]symbol [/color][color=Black]tempvar2 [/color][color=DarkCyan]= [/color][color=Purple]b8[/color]
[color=Blue]symbol [/color][color=Black]adc1 [/color][color=DarkCyan]= [/color][color=Blue]C.1
symbol [/color][color=Black]adc2 [/color][color=DarkCyan]= [/color][color=Blue]C.4

      setfreq m16
      pwmout [/color][color=Black]led,[/color][color=Navy]63[/color][color=Black],[/color][color=Navy]0
      [/color][color=Blue]readadc10 [/color][color=Black]adc1,random1              [/color][color=Green]'Seed for random command using ADC
      [/color][color=Blue]readadc10 [/color][color=Black]adc2,random2
      random3 [/color][color=DarkCyan]= [/color][color=Black]random1 [/color][color=DarkCyan]+ [/color][color=Black]random2
main:
      [/color][color=Blue]if [/color][color=Black]pushbutton [/color][color=DarkCyan]= [/color][color=Navy]1 [/color][color=Blue]then
            random [/color][color=Black]random1
            [/color][color=Blue]random [/color][color=Black]random2
            [/color][color=Blue]random [/color][color=Black]random3
            tempvar2 [/color][color=DarkCyan]= [/color][color=Black]random3msb [/color][color=DarkCyan]& [/color][color=Navy]7
            [/color][color=Blue]for [/color][color=Black]counter [/color][color=DarkCyan]= [/color][color=Black]random1msb [/color][color=Blue]to [/color][color=Black]random2msb
                  [/color][color=Blue]pwmduty [/color][color=Black]led,counter
                  [/color][color=Blue]pause [/color][color=Black]tempvar2
            [/color][color=Blue]next
            random [/color][color=Black]random1
            [/color][color=Blue]random [/color][color=Black]random2
            [/color][color=Blue]random [/color][color=Black]random3
            tempvar2 [/color][color=DarkCyan]= [/color][color=Black]random3msb [/color][color=DarkCyan]& [/color][color=Navy]7
            [/color][color=Blue]for [/color][color=Black]counter [/color][color=DarkCyan]= [/color][color=Black]random1msb [/color][color=Blue]to [/color][color=Black]random2msb [/color][color=Blue]step [/color][color=DarkCyan]-[/color][color=Navy]1
                  [/color][color=Blue]pwmduty [/color][color=Black]led,counter
                  [/color][color=Blue]pause [/color][color=Black]tempvar2
            [/color][color=Blue]next
      end if
      goto [/color][color=Black]main[/color]

eclectic · Nov 6, 2013

Another, using a parallel Piezo and LED

Code:

#picaxe 08M2

symbol centre = 128
symbol newval = b3

pwmout C.2, 63, centre

do
random W0

If b0 <= centre then
newval = centre - b0
gosub downwards

else newval = centre + b0
gosub upwards

endif

pwmduty C.2, newval

loop

upwards:
for b10 = 128 to newval
pwmduty C.2, b10
next
return

downwards:
for b10 = 128 to newval step -1
pwmduty C.2, b10
next
return

Sili · Nov 7, 2013

nick12ab said:

Yes you can use the random command so that the light dims down to a random amount or at a random speed. Here is some code that is not written very well and is uncommented but it does produce a random flicker and fade effect.

Code:

[color=Navy]#picaxe [/color][color=Black]08m2[/color]

[color=Blue]symbol [/color][color=Black]pushbutton [/color][color=DarkCyan]= [/color][color=Purple]pinC.3[/color]
[color=Blue]symbol [/color][color=Black]led [/color][color=DarkCyan]= [/color][color=Blue]C.2
symbol [/color][color=Black]random1 [/color][color=DarkCyan]= [/color][color=Purple]w0[/color]
[color=Blue]symbol [/color][color=Black]random1msb [/color][color=DarkCyan]= [/color][color=Purple]b1[/color]
[color=Blue]symbol [/color][color=Black]random2 [/color][color=DarkCyan]= [/color][color=Purple]w1[/color]
[color=Blue]symbol [/color][color=Black]random2msb [/color][color=DarkCyan]= [/color][color=Purple]b3[/color]
[color=Blue]symbol [/color][color=Black]random3 [/color][color=DarkCyan]= [/color][color=Purple]w2[/color]
[color=Blue]symbol [/color][color=Black]random3msb [/color][color=DarkCyan]= [/color][color=Purple]b5[/color]
[color=Blue]symbol [/color][color=Black]counter [/color][color=DarkCyan]= [/color][color=Purple]b6[/color]
[color=Blue]symbol [/color][color=Black]tempvar1 [/color][color=DarkCyan]= [/color][color=Purple]b7[/color]
[color=Blue]symbol [/color][color=Black]tempvar2 [/color][color=DarkCyan]= [/color][color=Purple]b8[/color]
[color=Blue]symbol [/color][color=Black]adc1 [/color][color=DarkCyan]= [/color][color=Blue]C.1
symbol [/color][color=Black]adc2 [/color][color=DarkCyan]= [/color][color=Blue]C.4

      setfreq m16
      pwmout [/color][color=Black]led,[/color][color=Navy]63[/color][color=Black],[/color][color=Navy]0
      [/color][color=Blue]readadc10 [/color][color=Black]adc1,random1              [/color][color=Green]'Seed for random command using ADC
      [/color][color=Blue]readadc10 [/color][color=Black]adc2,random2
      random3 [/color][color=DarkCyan]= [/color][color=Black]random1 [/color][color=DarkCyan]+ [/color][color=Black]random2
main:
      [/color][color=Blue]if [/color][color=Black]pushbutton [/color][color=DarkCyan]= [/color][color=Navy]1 [/color][color=Blue]then
            random [/color][color=Black]random1
            [/color][color=Blue]random [/color][color=Black]random2
            [/color][color=Blue]random [/color][color=Black]random3
            tempvar2 [/color][color=DarkCyan]= [/color][color=Black]random3msb [/color][color=DarkCyan]& [/color][color=Navy]7
            [/color][color=Blue]for [/color][color=Black]counter [/color][color=DarkCyan]= [/color][color=Black]random1msb [/color][color=Blue]to [/color][color=Black]random2msb
                  [/color][color=Blue]pwmduty [/color][color=Black]led,counter
                  [/color][color=Blue]pause [/color][color=Black]tempvar2
            [/color][color=Blue]next
            random [/color][color=Black]random1
            [/color][color=Blue]random [/color][color=Black]random2
            [/color][color=Blue]random [/color][color=Black]random3
            tempvar2 [/color][color=DarkCyan]= [/color][color=Black]random3msb [/color][color=DarkCyan]& [/color][color=Navy]7
            [/color][color=Blue]for [/color][color=Black]counter [/color][color=DarkCyan]= [/color][color=Black]random1msb [/color][color=Blue]to [/color][color=Black]random2msb [/color][color=Blue]step [/color][color=DarkCyan]-[/color][color=Navy]1
                  [/color][color=Blue]pwmduty [/color][color=Black]led,counter
                  [/color][color=Blue]pause [/color][color=Black]tempvar2
            [/color][color=Blue]next
      end if
      goto [/color][color=Black]main[/color]

ADC imput means that there are Pots involved?
I dont want to give input to the circuit! The values should be generated totaly random without a external input. Or is the code missunderstood by me?

eclectic · Nov 7, 2013

Try post #15 then.

nick12ab · Nov 7, 2013

Sili said:
ADC imput means that there are Pots involved?
I dont want to give input to the circuit! The values should be generated totaly random without a external input. Or is the code missunderstood by me?

No they are left floating. When left floating the ADC values will be somewhat random so it will prevent the flicker sequence being the same every time you turn it on.

Sili · Nov 8, 2013

I tried both of em now.

These are exactly what i needed! Awesome. I think im still deeper into the PWM thing now. i like it

Thanks for your help! i appreciate that!

Easy PWM Dimmer

Sili

New Member

Captain Haddock

Senior Member

nick12ab

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Sili

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Paix

Senior Member

Sili

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eclectic

Moderator

Sili

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eclectic

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eclectic

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Sili

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eclectic

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Sili

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nick12ab

Senior Member

eclectic

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Sili

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eclectic

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nick12ab

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Sili

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