Thursday, July 16, 2020

I2C Bubble Display Part III: It Works!

Hello again, time for Part III--using retro bubble displays for your audio (or any geeky) DIY project. 

This time we finish an I2C slave design that gets unsigned long (32 bit) values to show up on a 7 segment, 6 character LED.

The basic idea: use an Arduino Pro Micro to receive the I2C slave data and get the bubble display to show the 6 digit number sent to it.

Part I: I get the bubbles surplus (National Semi NSA1166--but the ideas here can probably be used on most any bubble or 7 seg display) and get it working with an Arduino, here;  how to get the 32 bit long data needed--when we are stuck in 8bit I2Clandia--from one Arduino to the Promini on the back of the bubble board--is here.

This time--I created a PCB for the Pro Micro, 74HC595 shift registers, a Bourns SMD resistor array and the bubbles--and it works!

Notice yellow kludge wire; I screwed up one of the pull ups for the 74HC595's on Rev1 6-14-20 of the PCB.  I'll fix that and post on my website. The chip on the far right is a Bourns 330 ohm SMD resistor array. 

Not that much to say--feel like I've met the goals. The pro mini on the board above does the heavy lifting to decode the incoming I2C. So I can send numeric data to the display using just 2 data lines and ground vs all the other ways to do this. One of the trickier things here is the bubble Eagle device had to be created from scratch, and the bourns array had to be modified as the pads were too small to manually solder. For the three or so remaining DIYers on the planet that still use Eagle vs. Kicad, a good tutorial on Eagle device futzing (from the technically dazzling dude--truly awesome stuff) is here.

Oh yeh I had one trace error which I fix here with a 30 gauge kludge wire; website has this correction already.

For tests, Uno as I2C master and Pro Micro on bubble board as I2C slave....

Building the bubbles: the damn thing didn't display the right numbers until I realized my code was sending bits to the shift registers in the wrong order! No, the ons and offs need to hit right 74HC595's in the right order for this to work.  As soon as I figured that out, it started to work.

Flip the display over--ah ha, Pro Micro clono!

What will I use this I2C retro bubble display for?  No idea.  I was thinking visual frequency output for a VCO? Pulse timer? Countdown display for something or other? Don't know.  But now that I can use an I2C device as a master for it, I have a lot of possibilities, which is always good.

This weekend I'll post schematics, PDFs, sketch code, BOMs etc. on my website. Update: DONE! go here. I feel an antique computer project coming next? Teensie audio?  Finish the noise! project? Too much to do but at least hanging out at the local pool hall isn't an option. Time gained back!!!

Until next time, don't breathe the bubbles.

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