The LM3914 LED bar graph driver was an amazing chip back in the day. Along with the LM3915, its logarithmic cousin, these chips gave a modern look to projects, allowing dancing LEDs to stand in for a moving coil meter. But time wore on and the chips got harder to find and even harder to fit into modern projects, what with their giant DIP-18 footprint. What’s to be done when a project cries out for bouncing LEDs? Simple — get a RISC-V microcontroller and roll your own LED audio level meter.
In fairness, “simple” isn’t exactly what comes to mind while reading [svofski]’s write-up of this project. It’s part of a larger build, a wavetable synth called “Pétomane Ringard” which just screams out for lots of blinky LEDs. [svofski] managed to squeeze 20 small SMD LEDs onto the board along with a CH32V003 microcontroller. The LEDs are charlieplexed, using five of the RISC-V chip’s six available GPIO lines, leaving one for the ADC input. That caused a bit of trouble with programming, since one of those pins is needed to connect to the programmer. This actually bricked the chip, thankfully only temporarily since there’s a way to glitch the chip back to life, but only after pulling it out of the circuit. [svofski] recommends adding a five-second delay loop to the initialization routine to allow time to recover if the microcontroller gets into an unprogrammable state. Good tip.
As for results, we think the level meter looks fantastic. [svofski] went for automated assembly of the 0402 LEDs, so the strip is straight and evenly spaced. The meter seems to be quite responsive, and the peak hold feature is a nice touch. It’s nice to know there’s a reasonable substitute for the LM391x chips, especially now that all the hard work has been done.
“harder to fit into modern projects, what with their giant DIP-18 footprint. ”
Young Me: Yah, I know I need to upgrade to SMD but I already have loads of old through-hole parts waiting to go into projects and not loads of money. I’ll change when my supply starts to run low.
Older Me: Ok, parts are getting more affordable and my salary is climbing. I don’t NEED to stick with through-hole but I don’t want to send all this to a landfill.
Oldest Me (so far): This stuff is ancient junk now. New stuff is almost free and does so much more. But… my eyes aren’t what they used to be. Tiny parts are lost in the blur!
I guess it’s DIP forever!
True that!
Haha, you just described my situation.
Now seriously, for me a life changing are helmet style workshop glasses. I tested few types from usual source „Ali” and the best are 2x magnification, but not really glasses , but a plate acrylic lens. Because it looks more like helmet harness with lens, you can put it so fast on head, with one move, and it perfectly fits as should. Much better than normal glasses, also because you can look below the lens if you for a moment do not need it. With glasses this is much harder.
I hope we all know what “Pétomane” means? If not, read this article and be enlightened:
https://en.wikipedia.org/wiki/Le_P%C3%A9tomane
Now that’s a talent!
Here’s another form of body music;
https://en.m.wikipedia.org/wiki/Manualism_(hand_music)
Thanks for featuring my project!
The synth is pretty convoluted — it’s a sport I like and I’m not even sure if it will work. But the level meter is indeed very simple and can be breadboarded in a few minutes, you only need the ch32v003 on a breakout board.