R2R Ladders

Repeater · Joined: Mar 19, 2011 Posts: 13 Location: Rochester

Could y'all chime in about the applications of R2R ladders in Lunettas? I understand what the circuit does and feel like I should build a couple, but I'm kinda stumped on what to use it for beyond mixing voltages going into CV inputs. It's kind of a mixer that plays favorites, right? Audio would be helpful as well!

tjookum · Posted: Sun Jul 17, 2011 2:13 am Post subject:

There is plenty of info on the web about R2R's, give it a search on google.

But basically it converts any binary input, like 0110 into the appropriate analog value. 4 bits give you 16 options and 0110 represents a 6, so the output voltage is at ±38% of Vcc.

ezekiel · Joined: Oct 17, 2009 Posts: 30 Location: Columbus Ohio

The R2R puts out a selection of voltages. The voltages are select by digital bits. Wikipedia and other places describe that.

As for Lunetta synth uses, here is one to get you started:

Take a binary counter (4020, 4040, etc.) and have it count up in a loop like 0000, 0001, 0010, 0011, ..., 1110, 1111, 0000, 0001, .... Then, hook the four output bits up to matching four inputs of an R2R ladder. The output of the R2R will be a stair-step sequence that steps from 0 volts up to the supply voltage, then jumps back down to 0 volts and repeats. Clock the counter slowly to use as a control voltage input to a VCO. Clock the counter fast to generate a rough ramp/sawtooth waveform. (With a little fiddling you might be able to figure out how to use a fifth bit to alternatively flip the waveform, creating a triangle wave--but still with 16 steps in it.)