Getting more than 8 CV outputs?

Rodrigo

So in planning for a bit of a hardware thing, I'm wondering if it's possible to have 10 CV outputs with a Bela cape. I'm specifically wondering about the 2 audio outputs. For my use case I'm not planning on using the audio output directly, so wondering if it's possible to convert the AC coupled outputs to DC coupled outputs to use those as additional CV outs. I guess the voltage range is a lot smaller too (2v vs 5v).

I guess there's also the multiplexer cape, but it would be a shame to sacrifice more sample rate than necessary. Don't know if it's possible to only set the amount of outputs in powers of 2 (so 16 in my case), which would bring the sample rate down to 11kHz from 22kHz.

giuliomoro

Rodrigo I guess there's also the multiplexer cape, but it would be a shame to sacrifice more sample rate than necessary.

That's only for inputs though, not for outputs.

Rodrigo For my use case I'm not planning on using the audio output directly, so wondering if it's possible to convert the AC coupled outputs to DC coupled outputs to use those as additional CV outs.

The J9 header carries differential, DC-coupled line outputs. These have a 1.8Vpp range, centred around 1.2V IIRC. On Pepper Rev B, a differential amplifier is used to obtain ±5V outputs from these. If you are not using Pepper, you could peruse its schematics to use as a starting point for a custom output frontend.

Rodrigo

giuliomoro That's only for inputs though, not for outputs.

Oh interesting!

The wording on the product page is a bit ambiguous where it reads as you can use 64 additional I/O (so up to 64 outputs if you wanted, with the same sr caveat).

So you can do, potentially, up to 64 analog outs (@5V) with 22kHz sr, with only increases of inputs requiring the downsampling?

giuliomoro The J9 header carries differential, DC-coupled line outputs. These have a 1.8Vpp range, centred around 1.2V IIRC. On Pepper Rev B, a differential amplifier is used to obtain ±5V outputs from these. If you are not using Pepper, you could peruse its schematics to use as a starting point for a custom output frontend.

Very good to know as well. Although 44.1k is better than 22k, if it works out of the box that way, that'd obviously be easier as I could skip. faffing around with voltage scaling.

giuliomoro

Rodrigo ambiguous

No, it's wrong.

Rodrigo So you can do, potentially, up to 64 analog outs (@5V) with 22kHz sr, with only increases of inputs requiring the downsampling?

No. The multiplexer capelet only works for inputs. Outputs cannot be multiplexed. So if you want 10 CV outs you have to use the 8 analog outs plus the 2 audio outs with suitable scaling circuitry

Rodrigo

giuliomoro No, it's wrong.

Definitely glad I asked!

giuliomoro So if you want 10 CV outs you have to use the 8 analog outs plus the 2 audio outs with suitable scaling circuitry

Ok, I'll have a poke around the schematic and see.

somedev

There is also the option of multiplying the number of available CV outputs by multiplying the number of bela units used. I am currently building a system that uses four belas that all receive the same 8 analog input signals, but each produces 8 different CV outputs. The idea is to use the digital inputs and perhaps a digital output from a master bela to control the multiple units as one 32 output channel unit. There is a lot of wiring involved in the multabela harness I am building to test this plan.