Buffer + Bypass "Quasi-IC" Module

So I finally had this design fabricated - and it works! Here's a build report where I used it.

I actually ended up changing the design considerably from what I initially posted. The overall concept is the same. But the main difference is that I decided to use a microcontroller for switch debounce, state management, LED lighting/dimming, and switching control. This turned into quite a detour, see mcu-bypass-firmware on GitHub. I have firmware for AVR Classic (ATtiny13a, 45 and 85), AVR XT (ATtiny202), PIC10F32x, and PIC10F675. I support three different switching schemes: simple CD4053/TMUX4053, x4053 with muting, and using a TQ2-L2-5V mechanical relay. I put a tremendous amount of effort into creating an exhaustive validation and test suite. This version 1.0 of the quasi-IC uses the firmware for ATtiny13a and the TMUX4053 with muting scheme switching.

I switched the intput/output buffer opamp to a OPA1678, and I gave up on having a dedicated IC for the VREF buffer.

You can see from the build report I had some self-inflicted pain just getting it installed and running correctly, but once my I got past my own bone-headed mistakes, the module works great!
 

Attachments

  • IMG_3330.jpg
    IMG_3330.jpg
    278.2 KB · Views: 23
  • IMG_3334.jpg
    IMG_3334.jpg
    345.3 KB · Views: 23
I forgot to update this thread with the newer evolution of this module, though it has been featured in several recent build reports. The first build report I posted with the newer module version is the Nashville Nobility.

The newer module is the same circuit as what I discussed previously, except it's been shrunk down to 16x43mm. The intent is to give the option of using right-angle pin headers so that it can be mounted vertically (i.e. perpendicular to the effect PCB). While the circuit is the same, the newer version uses the ATtiny202. It's my first time using that microcontroller (firmware link). I ponied up for 4-layer, ENIG finished PCBs, assembled by JLCPCB.

I've now used the newer module on several builds:
I'm super happy with how these turned out!

As a compliment to the firmware GitHub repo, I've also since created a new GitHub repo for the hardware designs: mcu-bypass-hardware.
 

Attachments

  • IMG_3647.jpg
    IMG_3647.jpg
    90.1 KB · Views: 3
Further riffing on this concept, I created an alternate true bypass version: it's still microcontroller based (using the same firmware), but has no buffers and uses a mechanical relay for switching. This brings me full-circle on bypass designs, as this very similar to my original MCU-based relay bypass design.

The updates from the original:
  • Better firmware
  • Better PCB design
  • I/O compatible with the quasi-IC, along with additional I/O for use with a lot of off-the-shelf PCBs (e.g. PedalPCB, Aion, etc)

The full write-up is here.
 
You must log in or register to reply here.
Back
Top