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### Topic: Matrix problem (Read 5241 times)previous topic - next topic

#### bogdan666

#90
##### Apr 20, 2019, 01:40 pm

Yes, it works perfectly, now obviously in real life it looks better than on camera, i still have to test the current draw from leds and settle to a value, i can make it a bit brighter i think, the resistors on the right are shorted(it was easier for me to cancel them)
About the code, i understand how it works now, i will play with it more to see what changes in order to understand it better. Paul i cannot thank you enough, you have been very patient with me and helped me a lot, the world needs more people like you. As you can see, i have 2 potentiometers and one button soldered on the board, so i am guessing i could do the speed of scrolling with one potentiometer, and with the button, maybe go to next text

#### PaulRB

#91
##### Apr 20, 2019, 04:01 pm
I can't see the resistors on the columns. What value are they? You need to limit the current to around 2mA per led, because of the 35mA limit of the individual '595 pins. So these resistors need to be around 1.5K.

Have you got room for 8 transistors where those shorted row resistors are now? You could use 8 bc337 transistors as emitter-followers. No base resistors would be needed. Then you could use lower resistors on the columns. You could allow 8mA per led, 4 times brighter than the current circuit. The column resistors could be much lower at (5 - 2 - 0.7) / 0.008 = 288R

#### bogdan666

#92
##### Apr 20, 2019, 08:40 pm
The resistors are on the back side, 1.5k, i didn't have much room on front, as for the transistors, maybe if i remove the resistors i could get them in there, it would be very crowded

#### PaulRB

#93
##### Apr 20, 2019, 09:43 pmLast Edit: Apr 20, 2019, 09:45 pm by PaulRB
The transistors are only slightly larger than those resistors, but they have 3 leads rather than 2. You would connect the base lead to the '595 output pin, the emitter to the led row and the collector to 5V.

#### bogdan666

#94
##### Apr 21, 2019, 07:29 am
ok, i will try to get them on the board next week, but i will use 2n2222, they are similar, and i have a bunch of them

#### PaulRB

#95
##### Apr 21, 2019, 08:04 am
2n2222 is fine. Before you change the column resistors, add a transistor to one row and check that the display works as before. Then add the other 7 transistors and test again. Finally, change the column resistors to 300R or 330R.

#### bogdan666

#96
##### Apr 21, 2019, 08:36 am
ok, i will, happy Easter Paul.

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