32 Bi-Colour LEDs Christmas Tree


Posted on Jan 19, 2013

Next is the microcontroller or MCU. In previous projects, we used the Atmel AT89C2051. However, the I/O port structure is not quite suitable for this application so we have used the similar Atmel AT90S2313. The main feature influencing this decision is that the 2313 outputs can be `turned off` while the 2051 outputs always have pullups enabled. When I said the 2313 is similar to the 2051, I was referring to the arrangement of I/O pins and their functions. Inside, the two chips are quite different. See the sidebar `Whats in the AT90S2313` for a description of the microcontroller. U3 (24C16) is a serial EEPROM where the pattern data is stored. While the 2313 has some EEPROM on chip (128 bytes), this was not enough for the number of patterns we wanted to provide. The final block is, of course, the LEDs. At first glance, the PCB looks like it contains 32 LEDs. In reality, there are 64 LEDs as each is a bi-colour LED capable of glowing red or green.






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