After failing to get the 74LS174 board working, I decided to go with the flow and build a 74HC595-based LCD driver board instead. There are plenty of examples online, from Adafruit to Steve Hobley to Rowan Simms — this will be a cinch!
So I built out the schematic, ran all the traces, did all the art and etching (things went a little better with the wide traces, but I still need to look into better peroxide), populated the board, and… nothing.
You’ll carefully note that I didn’t say “hooked up the 595 on a breadboard to test the circuit first”, because I didn’t. I copied the designs from the ‘net, and triple-checked my work, I thought, but … oops.
So I was pretty bummed out; more bricked boards lying around, a lot of work down the drain, etc.
And I eventually got around to testing the thing thoroughly. First, I hooked up a ‘595 on a breadboard, following my schematic layout to the letter. Predictably, it didn’t work. OK, so I needed to figure out where the problem was (bad ‘595? fried LCD? Buggy schematic?).
I went back to basics.
First, I hooked up the LCD to the breadboard and wired it to the Arduino with a full 6-wire circuit, just like LCD bootcamp.
That worked fine. And I confirmed that I hadn’t fried any of my screens with my messing around — whew.
Then I hooked up the ‘595 carefully and noticed that one of my wires which I’d taken to 5v was hooked to ground in another post, so I tried that, and … no dice.
Hmm.
Then I looked really carefully at *which order* the shift register pins were hooked up, and realized that I’d hooked the data pins up exactly reversed (3210 instead of 0123). That’s a software fix (unless you’re going to redo the board layout), and I tested the software fix… and it worked! Nifty. Now I have a working, breadboarded circuit.
So I checked the board, and everything looks fine.. except that one pin that’s HIGH instead of LOW. So I have to cut the trace and put in a GND jumper. I fixed it in the schematic and my board layout, so next time I etch it, I’ll hopefully get a working board right off. Oh, and I had to put in a jumper, because I had an orhpaned GND plane. yuck.
So I’m ready to roll, and I think I’ve debugged an etched board. Pretty cool. Watch this space for photos of the whole thing running. Once I get it running.