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how would i wire my 5x7 led matrix to work with 74hc595 and arduino? Answered

i have a really neat 5x7 led matrix from a recycled led sign from a surplus store and the rows are anodes and the columns are cathodes. i would like to get it working so that i can display messages on it.


You'll struggle to get a 595 to drive the LEDs, since the forward fdop is likely to be > 5V for these triplets of LEDs. When I made an almost identical panel, my drivers needed ~8V I think.


couldn't i use transistors to source 9 volts. the forward voltage is 9v

You'll need to create sourcing and sinking drivers, assuming you want to use them in a matrix. A "high" voltage sourcing driver is going to take at least two transistors per channel - an NPN from the 595 and a PNP to the LEDs. The sinking driver can just be a ULN2803. A best solution would be Allegro's A2981 for the sourcing and an A6278 for sinking. Steve

See the various instructables that describe multiplexed/matrix LED displays. You've already figured out the anode/cathode wiring, so all you need is the driver hardware to enable (and present signal to) one row at a time, plus the program to cycle through these sets of 12 bits (and a bit more software to update what that loop presents).