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The Inevitable Design Oversight

A project log for Weather Display

A WiFi-enabled wall-mounted lighted display for current weather conditions

techavtechav 11/30/2015 at 04:300 Comments

It was my intention all along to use two or three RGB LEDs per segment of the weather icon. The TLC5940 is perfect for driving multiple LEDs—constant current outputs capable of sinking up to 30 volts. But of course this assumes discrete LEDs. Common anode RGB LEDs cannot be wired in series to the different outputs. I wasn't thinking about that when drew out the schematic, wrote the display driver code, tested the display driver on the breadboard. This means I will need two TLC5940 chips so I can put two LEDs in each icon segment. The protoboard I'm working on will fit two 28-pin DIPs with plenty of room for supporting components. Three 28-pin DIPs is a very tight fit. If I could drive the TLC5940 from the ESP8266, this wouldn't be a problem at all. I am definitely not going to be figuring that out any time soon though.

From what I've read so far, there's still quite a lot of debate over whether the ESP8266 has one PWM pin, or four PWM pins or no hardware PWM. At any rate, the PWM pins listed are the same as the SPI pins, and the SPI pins would be needed for shifting in the pixel data to the TLC5940. I'm sure it could be done, but again, programming is not my strong suit.

So, I will be attempting to fit three 28-pin DIPs into a 17 by 14 protoboard space, with 9x6 left to the side for support components like the crystal for the AVR, pull-up resistors, etc. It will definitely push my point-to-point wiring skills. I think some of the things I learned wiring my Z80 computer will help though.

I've drawn up my working schematic in Eagle and inserted it after the break.

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