LED fader

[russbow]

I want to fade a string of christmas leds and found this in a forum search

http://www.picaxeforum.co.uk/showthread.php?t=12471&highlight=rgb+fader&page=2

As the lights take 100mA or so, the sample circuit isn't meaty enough. So I hooked up an L293 driver chip, the 08m outputs taken to the driver inputs and the LED strings connected between the driver outputs and 0 volts. The pwm pin2 of the 08m is connected to both the enable pins of the L293.

Using this code, I was pleased with the initial results.

'RGB LED Display
'PICAXE-08M

let dirs = %00010111	'set all used pins to outputs
main:



let pins = %00010000	'4
gosub fade

let pins = %00000001	'0
gosub fade

let pins = %00000010	'1
gosub fade

let pins = %00010001	'0,4
gosub fade

let pins = %00010010	'1,4
gosub fade

let pins = %00000011	'0,1
gosub fade

let pins = %00010011	'0,1,4
gosub fade

goto main

fade:	
	for w1 = 0 to 300
	pwmout 2,99,w1
	pause 20	'increasing brightness
	next w1
	pause 1000
	

for w1 = 300 to 0 step -1
	pwmout 2,99,w1
	pause 10	'decreasing brightness
	next w1

	
	pwmout 2,99,0
	pause 1000
return

I then thought that a bit of flashing might be nice so I extracted part of the above code and added a flsh routine.

'RGB LED Display
'PICAXE-08M

let dirs = %00010111	'set all used pins to outputs
main:


let pins = %00010011	'4
gosub fade

gosub flash
goto main



fade:	
	for w1 = 0 to 300
	pwmout 2,99,w1
	pause 20	'increasing brightness
	next w1
	pause 1000
	

for w1 = 300 to 0 step -1
	pwmout 2,99,w1
	pause 10	'decreasing brightness
	next w1

	pause 1000

return


flash:

for b6=0 to 5
toggle 2
pause 500
next b6

return

Doesn't work !!

If I just rem out the gosub fade, the LEDs flash. If I just rem out the gosub flash, the fade works.

If I leave them both in, the LEDs fade O.K. and then there is just a pause, with all LEDs off during the flash time.

Looks O.K. in the simulator.

Any ideas please.

Russ

 

[Haku]

Add this to just after the "flash:" line:

pwmout 2 off

 

[westaust55]

With all these fading and flashing lights, which house is yours?

 

[russbow]

Westy, you can't see mine. It's the dog house round the back !

 

[russbow]

Haku, thanks for that, spot on !

Would never have thought of that. Of course, have now looked in Man 2 and found it, but wolud not have given it a lot of significance if I'd spotted it before.

Why wouldn't let pins = %00010011 give me the same result?

 

[hippy]

Why wouldn't let pins = %00010011 give me the same result?

"Let pins=" simply requests the output pins to be set to a specific value and doesn't affect anything else within the chip, in this case doesn't disable the PWMOUT which overrides the pin 2 output once it's been enabled.

It's done this way so you can use PWMOUT and "Let pins=", or using the later would always disable PWM, forcing output to be low or high depending on bit 2 of the written value.

 

[russbow]

Thank you all for your inputs. I now understand the process.

Of course it raises further questions about pwm, pwmout, hpwm but I think that's for a separate thread later after a good forum trawl.

For now, all done and dusted. Thanks.

73s Russ

 

[boriz]

"I hooked up an L293 driver chip"

Almost any medium power 10Pence transistor would work.

 

[russbow]

Yes of course Boriz. The original used trannies with the bases PWMd but I needed 100mA per string. It was easier to switch the strings with the 08M outputs and PWM with the L293 enable pins. Besides, if you've got, use it.

R.