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Topic: big LED matrix, 32 x 24 LEDs (Read 960 times) previous topic - next topic

takao21106

This is a project I am working on currently.

768 3mm LEDs.

It is difficult to solder the rails for the rows, some shorts are unavoidable,
and it's hard to take out solder without to cause more shorts.

I don't have much solder wire left, about 20 grams,
while the matrix board has increased weigth considerably.

The plan is to have 8 different brightness level, it's a bit weird since
3 bits are used.
I also have PIC related web domain.

takao21106

adding a 3.3 volts power supply.

It is powered from 5 volts now, later I want to use a 12v electronic transformer

There is no cooling grid but a small fan under the voltage regulator.

I want to get some experience how much heat is produced and how much can be cooled away.

Right now connected a smaller matrix that I built some years ago, using standard LEDs (not high brightness). It works at 5 volts but also at 3.3 volts.
I also have PIC related web domain.

CrossRoads

You can calculate how much current will be needed.
It will be based on how many LEDs can be on at one time.
That is based on how your are multiplexing.
Your array seems to be 24 LEDs  high and 32 LEDs across.
I would call that 24 Rows, and 32 columns.
I would also guess that you drive all 24 rows, and enable a column on & off.
Then drive the row data for the next column, and turn the column on &  off.
Repeat for the remaining 30 columns.
That would mean you  have 24 LEDs x 20mA/LED = 480mA.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

takao21106

#3
Mar 10, 2012, 01:38 pm Last Edit: Mar 10, 2012, 01:57 pm by takao21106 Reason: 1
No, I drive 32 Columns at once, but only activate one from 6 rows.

For 24 rows, 4 rows are active at any time.
I am not sure about 20mA limit.

This is why I have the capacitors, and the 3.3v regulator.

The smaller matrix by the way, has 2 rows active at any time. It is a mess to program it in PIC RISC, even using 18F chip. I made the clock working but then just did not put more efforts into the project anymore.

Now I want to use 4 smaller controllers for the refresh/buffering, and 8 brightness levels.
And one bigger controller as the master, using the hardware serial port of the smaller devices to send them data. It is not easy because all 4 must be synchronized. Initially I will let them run unsynchronized to see how it looks like.

I am close to testing 1/4 of the matrix using only one controller.
I also have PIC related web domain.

CrossRoads

"No, I drive 32 Columns at once, but only activate one from 6 rows."
"For 24 rows, 4 rows are active at any time."

So, at most 24 LEDs could be on at one time?

Okay, so  4 * 6 * 20mA (max current on most LEDs) = 480mA
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

takao21106

#5
Mar 10, 2012, 05:37 pm Last Edit: Mar 10, 2012, 05:39 pm by takao21106 Reason: 1
32 LEDs/row

24 rows

4 rows active at any time

32*4 = 128 LEDs

128 LEDs x 30 mA = 3.84 Amp

This is why I go down to 3.3 volts.
At first 1/4 of the matrix will be activated, and I'll see how much heat is produced.

It is a lot of effort to wire the shifting registers.
Today I completed the column wires for 32 columns, nearly no solder left.

Found some more 74hc164 installed them too, there is only one more of them required.

Added capacitors everywhere, most are 100uF some 47uF, 220uF and 470uF.

And I am thinking how to implement 8 brightness levels.
The idea is to get 3 bits from 3 bytes, and build the countdown variable.

There are only 128 bytes RAM inside the controllers I use.
The refresh frequency needs to be 1 KHz or so.
I also have PIC related web domain.

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