inverting the DOUT pins

[cimo]

hi

i was smart enough to order bicolor leds with common anode for my MBLC, so my question is:

-is it possible to change the software (MBLC) to invert the DOUT pins and use them as current sink ?

.. i ve read that the ST boards can be fitted with darlington arrays, but in my case i won t need that since 1 DOUT pin will sink only 1 led

Simone

EDIT: i a interested in knowing how to do this but i am also looking for other leds with common cathodes, that would probably be an easier solution.

[/tilted/]

Look for this inside LC_LEDS:

[tt]LC_LED_Set_Loop_LEDOn

movf LC_LED_LOOP_CTR, W

call MIOS_DOUT_PinSet1

rgoto LC_LED_Set_Loop_Next

LC_LED_Set_Loop_LEDOff

movf LC_LED_LOOP_CTR, W

call MIOS_DOUT_PinSet0

;; rgoto LC_LED_Set_Loop_Next

[/tt]

And change to:

[tt]LC_LED_Set_Loop_LEDOn

movf LC_LED_LOOP_CTR, W

call MIOS_DOUT_PinSet0

rgoto LC_LED_Set_Loop_Next

LC_LED_Set_Loop_LEDOff

movf LC_LED_LOOP_CTR, W

call MIOS_DOUT_PinSet1

;; rgoto LC_LED_Set_Loop_Next

[/tt]

This would work assuming all your leds are the same.

If not, (ie a mix of bicolour and normal), then reverse the polarity of the normal LEDs, and tie their anodes to VCC instead of GND.

I think this would work.

[doc]

If it won't work as /tilted/ said, here a hardware solution:

Drive the bicolor LEDs through a ULN Array (see: midio128) and you have a common anode ...

greets

Doc

[/tilted/]

I'm also working on an idea using an inverting buffer to do a similar trick.

I haven't tested it yet, but of course have already started the design for the PCB... :P

so my theory goes:

[tt]

Vpot matrixed cathode 595s +--->  Inverting Buffers ---> Vpot cathodes (blue)

                           L--->  Vpot cathodes (red)

                                  Bi-Colour LEDs

Vpot/meter anodes <-------------  Common anodes

[/tt]

I just hope the anode 595s can sink enough current... else I'll need to use transistors.

This would mean that the V-Pots have a red pointer, with the remaining LEDring glowing blue.

[doc]

I just hope the anode 595s can sink enough current...

... 10...15mA per Output. Not more!! .. or you'll fry them.

For more current use transistors (or ULN Arrays)

greets

Doc

[stryd_one]

WIKIMARKER

I always wanted to do that.

[cimo]

  mmmmm .... fried 595s ...

emmm.... ok 10-15 mA isn t that much after all, i am somehow stuck to this point with the PCB layout.. deciding if i d better leave space for 4 pins (2 leds) or 3 pins (bicolor) or 4 pins again (RGB using only 2 colors).

I am really tempted to "bring home" this little piece of knowledge but buy some other leds for this purpose.. and go safe

txx

Simone

[cimo]

... i will go for the software solution and use the common anode bicolor leds, i cross my fingers... BUT one of the DOUT pins will drive 16 leds, in this case i have to use a transistor: a sink DOUT pin that will drive a sink transistor (dunno if my terminology is correct)

-will this work?

-can you name a transistor for this purpose?

Simone

EDIT: a little bird s named bc547 (max 0.2A) will that stand 32 x 20mA leds, limiting the current of course...

  do you know a bigger brother of the bc547?

[TK.]

BC337

(one part is already stuffed on your core module)

Best Regards, Thorsten.