I was recently building a dual logic module by Barton, BMC040 Dual Logic. This module offers two 2-in-1-out logic gates with a knob for adjusting the logic gate type (AND/NAND/OR/NOR/XOR/XNOR). I realised it’s adjustable logic gate type is implemented as a analog voltage being read by a PIC.

Here’s the original circuit:

(non-orthogonal lines in a schematic should be illegal, but that’s a different story…)

Notice how L1 and L2, the potentiometers setting the gate type, are just voltage dividers between GND and 5V. This got me thinking, I could add voltage control to this and make the module 100x more versatile. And while I’m at it, I’d like to add some visual feedback on the selected gate type.

So this is what I came up with:

The CV input is just a simple sum of a CV with an input attenuator and a manual setting. The ‘Mod connector’ will connect in place of potentiometers L1 and L2 (I’ll build the whole circuit twice). The indicator leds are a bit of my improvisation…

The idea is a ladder of comparators dividing the 0-5 rails in 6 equal parts (corresponding with the 6 gate types). All opamps referencd below the CV will be driven high, the ones above CV will be driven low, meaning that exactly one LED will light up.

I have googled, but I have no idea what this type of arrangement is called. Does anyone here know? Or do you maybe know a simpler way to implement this (perhaps with discrete transistors?)

Thanks!