On Wed, Jul 28, 2010 at 11:42 AM, vasi vasi <[email protected]> wrote:
> Hi Joep and Vasile, > > This is the scrolling text: > "HELLO JOEP And VASILE _ THIS USE Your LibrArY" > > http://www.youtube.com/watch?v=RatJm6wGxpI Oh boy, you are a rested (hodinit) guy too...:) > > > I wanted to learn how to use 4 digits as a decent display and for this, I > used also timer0_isr_interval.jal (to light another 8 LED's at different > speed) because I don't know yet another method of "multitasking". > I use FreeJALduino with EvB 4.3 version 4 board (with already bricked > ATmega :( ) and entire assembly draws very much current, the onboard 5V > regulator gets very very HOT. An external source of 5V is obligatory for > this kind of application. > Anyway, the conclusion is: It is too much trouble and too many pins > allocated for this task. :) search on the internet for "gugaplexing", "charlieplexing" and other "plexing" methodes... > It require a separate microcontroller for this and in this case, you can > transmit data on serial. For 4 digits and 8 LEDs I used all available pins > on FreeJALduino and the DOT from digits remained unconnected. But the > experience gained is invaluable. > > The segments get lighted on 0 logic and also digit selection is made with 0 > logic (I don't know how to draw a schematic for this). The LED's are lighted > also on 0 logic (this is easy, but program inside is for 1 logic - I must > negate the byte). In the movie, the digits are lighted one at the time, > 350uS long each but I modified the program for 950uS each to get rid of that > echo. If is useful, I think it can be easily modified for Jaluino. All > required files attached. > Vasi, this is calling "ghosting". I've written an article about this problem but right now is in evaluation at the IEEE-Micro magazine, maybe they will reject it too, so you'll see it on my blog.... (I really hope not). In a few words: as you can see from your movie, even taking a photo or a movie to a multiplexed display is a difficult task. Depending how display is routed to the PIC IO, there will be a ghosting situation, except if using standalone 7seg drivers between the PIC and display. The reason is the variable voltage level on pins when they are used as input (pseudo high impedance or highZ, PIC/Atmel does not have a true highZ output circuit as old logic buffers have). A LED connected between two input pins of a PIC will light, and this is ghosting caused by un-fixed voltage level (if all highZ would have for example the theoretical VDD/2 voltage level fixed -used in all drawings-, that would not happen). The second cause of a ghosting is a bad timing multiplexing. Switch from one segment to another using highZ (meaning input), switch from one anode(cathode) to another anode(cathode) through an OFF state. The time which one display lights gave the overall current drawn. A good choice is 1mS to 3mS for standard display, less than 1mS for high efficiency display. Between switching a shut OFF time of 50-100uS is reasonable. Vasile -- You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
