Peter Wintulich wrote:
>
> I thought of some possable ways of reducing the number of
> control lines required to opperate a led matrix.
>
> 1) Using a 47hc4017 as a colum driver in various ways:
>
> A) Drive the clock lines seperately one for each LED colour,
> and have a common MR (Master Reset).
>
> B) Use a common clock line but seperate MR's one for each
> colour.
>
> C) Cascade two 4017's having one clock & one MR line, and
> interlive the collums of LED colours. PIC port RB could
> directly drive the row of LEDs via current limit resistors.
>
>     After thinking about the above options I thought the colour
> mixing would be too messy & not officiant.
> (option C seamed simplest but would only light 8 leds at a
> time.)
>
> 2) Using 74hc374 (Octal Latch) for each LED colour.
>     This would allow 16 LEDs to light at once (giving a brighter
> display) & is easy to get colour mixing. This uses PIC port
> RB as an 8 bit bus, which is connected to the inputs of each
> Octal Latch & directly to the collum drives (For up to 8
> collums). Two other PIC O/Ps are used to latch the data into
> each Octal Latch. The -OE (Output Enable) lines of the
> latches could be tied LOW, always enabled.
>
> For a wider display:
>
> A) For 10 collums use the two PIC O/Ps that Opperate the
> Octal latches as the latches are  rising edge triggered. Only
> Reset the lines LOW if you don't want them high.
>
> B) Use a shift register or equivelent to the required bit length.
> The clock can be one of the Octal Latch latch inputs. The
> reseting of the shift register could be by a seperate PIC O/P
> or by an AND, OR or NOR of the two latch lines for the Octal
> Latches.
>
> C) A combination of  using RB lines & a shift register could
> be used to keep extra components to a minimum.
>
> 4017's make OK for collum scanners (active high o/p), they
> can be cascaded although this could reduce their effective
> width to 8 or 9 bits depending on how they are connected
> together.
>

Something you could consider, is to hook a bicolour (two terminal)
LED to the output of a common inverter gate, and a voltage divider.
By driving the input high, low, or toggling, you can create a couple
of colours. Power the inverter from 10V.

--
Friendly Regards

Tjaart van der Walt
mailto:tjaart@wasp.co.za
 _____________________________________________________________
| Another sun-deprived R&D Engineer slaving away in a dungeon |
|             WASP International  http://wasp.co.za           |
|             GSM and GPS value-added applications            |
|  Voice : +27-(0)11-622-8686   |   Fax : +27-(0)11-622-8686  |
|_____________________________________________________________|