How Dottie Was Made
My trusty Arduino (it’s red, a clone from Sparkfun, and it was on sale for $10) begins this journey to reverse-engineer a flip-dot board. I figure that if I can flip one single dot, using a shift register and a couple of transistors, then all I need to do is replicate that across 25 columns and 7 rows… right?
Thus began numerous attempts – I think seven in total – to figure out how exactly the board works. In this iteration, I’m trying to get a couple of shift registers to open a bank of TIP-120 transistors to send some volts on their way to the board. It gets complicated because the voltages have to go down different physical lines depending on whether you’re flipping Black-to-Yellow or Yellow-to-Black.
Turns out that 14 TIP-120s (one for each of the seven rows of dots on the board, multiplied by 2 because of the physical lines) didn’t work. I could get the flip to happen one way (sometimes) but not the other way. Potentially, my circuit design was faulty as well. Hellooo, no diodes?!
Despite these problems, the circuit is beginning to take shape. From the far left:
Shift registers to ultimately control 25 columns
H-Bridges to handle the reversing of polarity that’s needed to flip both directions
A couple more shift registers to handle the 14 rows (7 x 2) and the transistors to power each row
For more detail: Dottie the Flip Dot Clock