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DOT MATRIX-time share limitation

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rahat

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increasing the brightness of dot matrix

i hv made a setup for a 8x8 dot matrix. i want to increase the no. of 8x8dot matrix block with the same microcontroller.but the problem is, as we know ,we hv to time share in dot matrix,if the no. of rows increase, the time alloted to one row will decrease,as a result,the brightness of row will decrease.how can i approach to maintain the same brightness but increase rows of led(dot matrix block)?
 

circuit for increase brightness in dot matrix

thnx for the info.

the leds are connected to the micro controller through buffer(ic4050).as i mention previously, the on time of the leds(in a particular row) decrease with the icrease of rows(new led block).hw can i increase the current during the ontime of the led,as the voltage are fixed?plz mention any procedure to maintain the brightness of the leds.
 

time sharing led

Hi,
You reduce the value of LED series resistor, or use a high voltage buffer, increase the volatage and select suitable series resistor to adjust the LED current.

Regards,
Laktronics
 

    R

    rahat

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dot matrix time

I presume there are current limiting resistors to the LEDs.

If you halve the on time for the LEDs then you have to double the current and you do that by halving the resistor value.
 

    R

    rahat

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limitation of time sharing

thnx to all repliers.

the leds are connected directly to buffer(no resistance inbetween).as per Iakelectronics,i may incr the volt of the buffer.plz mention any other procedures if possible.
 

dot+matrix+time

I see from your other post that you are using a 4050 as a buffer.
That will limit your current to a couple of mA. You will need to redesign your circuit to increase the current.
 

if you increase rows to lets say 16, you will be doing 1/16 scanning mode for the display. Currently you are doing 8.

Now if you want to keep a refresh rate of 50Hz, meaning 20ms for iteration of 16 rows. You should process everything from serializing data to cols for each row to putting each row off and next one on for all 16 rows in 20ms. ie 1.25ms for each row. Do the calculations accordingly and you will need a fast controller.

This is not advisable though (I havent tested this, so i dont know if this should work practically, theoretically it should). For such cases, usually a master slave configuration is required where 2 controllers run two sets of 8 rows. And a master controller sends data to these 2 controllers.

xtech
 

    R

    rahat

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Thnx to xnox_Rambo and Huzaifahm.
The description huaifahm, you gave,i am trying exactly that thing.(i.e. i have now 16 rows(previously 8 ),but i want to maintain the brightness)

To Rambo- by 'redesign' did u mean to change the buffer ic only?or do i hv to make other changes?

To Huzaifahm-by fast controller did you mean microcontroller with higher clock rate?i dnt understand ,hw the 2 controller(?) will work?Plz can u clarify?
i m using Atmega32.
 

rahat said:
Thnx to xnox_Rambo and Huzaifahm.
The description huaifahm, you gave,i am trying exactly that thing.(i.e. i have now 16 rows(previously 8 ),but i want to maintain the brightness)

To Rambo- by 'redesign' did u mean to change the buffer ic only?or do i hv to make other changes?

To Huzaifahm-by fast controller did you mean microcontroller with higher clock rate?i dnt understand ,hw the 2 controller(?) will work?Plz can u clarify?
i m using Atmega32.
Click to expand...

Yes, higher clock rate should do it, but a flicker free displays needs accurate delay adjustments and good refresh rate. It is achieved using the formula I told earlier. You need to successfully display each row in 1.25ms.

About 2 mcus, you will need to interface controllers using serial transmission. I have seen it work though I have not tried it. The idea is that master controller sends data to each slave synchronously. Each slave decodes that data to font and fills cols and multiplexes 8 rows.
 

    R

    rahat

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thnx to huzaifahm again.

in my design, the columns of the two block(8x8 dot mtrx) are conneted to 8 pin of the ucontrlr thrgh buffers(i.e. the 16 column are connected to 8 pin).at present, the two set of rows(8 each) are connected to 2 port of the ucontroller(i.e. to 16 pin of the ucontrlr). now i m sending data from ucontrlr to the 16 rows serially(1st row,2,3.....15,16,1,2,....).
according to ur suggestion,i should use two controller for the two set of rows(may be i misunderstood).can u plz specify the type of controller?and also plz mention where to connect the rows(2 set,8row each) and the columns(2 set,8clmn each,presently connected together in 8pin of the ucon.).

plz mention the sites(if any),where i wl get the details abt connection of this design with controller.
 

hi,
can anyone plz gv any direction(without incr volt of buffer)?

regards..
 

Please use ULN2003 and 74HC164 to serially shift data into columns. Use a 3-8 decoder like 7445N to put one row ON each time. This way you will need only 2+3 pins from the MCU unit to run a display with 12 matrices. ULN will take care of the current sink at columns. You will need PNP transistors like BDX54F at rows output to source the rows.

Using this design will be 1/8 scanning method. To use 1/16 method, use a 4-16 decoder. rest will remain the same, but brightness will decrease because each row will be ON half the prev time. So eiher do the delay calculations right, OR use another design(I only gave the 2mcu idea earlier, I don't know exactly how it will work.)
 

    R

    rahat

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thnx to huzaifahm again.

i m wrking with the shift register concept.

regards...
 

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