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When I saw the 120-LED matrix display 18050 OP from MPJA for $1.95, I could not resist buying 5 of then, without any idea what I might do with them. This device is a contrivance just to justify the purchase. While it is theoretically possible to drive each LED individually, it would take a ridiculously large amount of interfacing, and a picaxe would be too slow. Even making contacts with these devices is a problem, as each has 30 thin wires, not rigid pins. To stiffen them I cut a unused board made for SRAM into 10 strips and soldered them onto the wires, leaving space to make connections with thin wire-wrap wire (but soldered). The compromise was to wire together all the 10 rows of green LEDs into left and right halves, and to make six groups of the top rows, which have red and orange LEDs. This reduced the matrix to 8 source drivers and 6 sink drivers. I used a CD4028 to decode the sink drivers, and a 74LS138 to decode the source drivers, which reduces the control requirements to six bits, plus two for the green LEDs. These 8-bits go to a connector to give flexibility in implementing a separate control board. In the end I got tired of all this work, and after designing 3 alternative controls, I settled for a picaxe 08M and a 74HC595 to generate the 8 bits. A pot gives a manual input which can be used in many ways. The initial program shown oscillates the green bars right and left, blinks all 600 LEDs, and then sweeps the top row to the right. This does not exist anymore. The enclosure was used for the Pedestal Clock. |
| Here are photographs |
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Here are the circuit diagrams |
| Here is the code |