Is my nifty MIDI VCV-like sequencer idea plausible?

Hey guys! I need an opinion about my project, i'm really fond with the idea but i lack the experience to understand if is plausible or not (it's my second project).

Being an avid VCV rack player, i want to replicate the VCV rack sequencer!!!!

So my specifications are:

  • USB-midi controller built using Arduino Leonardo. It will send midi notes to the software.
  • The notes will be controlled by a single row of 8 pots, with 8 leds and 8 switches that can disable/enable the single steps (i'll clearly need a couple of mux, i think a 16 digital and 8 analog)
  • The controller will have a BPM knob and a display to control the tempo, a knob to control gate length of the notes plus a reset button to make it start from the first note. The controller will not have any synchronization with the software.

Is it a good idea? Or am i going to have tempo problems, with the unit losing beats?

I know that probably i'l get better results with a vanilla usb controller hooked to the VCV, but this is just the beginning, if i'm succesfull i'll build another one with multiple rows, an internal note quantizer, some pots to control the VST synth and probably a random knob, and add other nifty crazy stuff.

Sounds OK but don’t use a multiplexer for an LED output use a port expanders or a shift register.

Hey Think gli and advice us welcome! Since I have 8 analogue inputs (the pots), 8 digital in and 8 digital out I thought from a quick Google to use a couple of cd74 mix. Could you explain why I shouldn't use them? For learning purposes! Anyway thanks man

Could you explain why I shouldn't use them

Using a multiplexer for an output is stupid because only one LED is going to be on at a time unless you revert to driving them as a multiplexed output. Now I know you might be thinking you only need on LED to be on at a time but for future development you might need more than one. Also the normal multiplexer chips are not designed for driving loads, but signals. They have a relatively high connection resistance and low power dissipation which makes them unsuitable for driving LEDs directly. These parameters change from strip to strip.

Using multiplexers for analogue inputs is fine. They are then driving the very high impedance inputs of the A/D converter and the connection resistance in comparison is very small.

Do not use the old chips with CD at the start of their names for either. They are obsolete in their performance parameters, but I know from experience some eBay traders advertise the proper chips but send you the CD type. You should be looking for the 7HCT type of chip.

That's 74HCxx family, not 74HCTxx.

What is wrong with the 74HCTxx devices?

HCT only work at 5V (not battery friendly), they have less noise-immunity as the inputs are
TTL compatible, and they are more expensive and less easily sourced. They are designed
for interfacing to legacy 5V TTL, not general purpose CMOS logic, hence the T in the name.

They do have a use as 3.3V to 5V level shifters as the input thresholds happen to work for this.

HC family run from 2V to 6V with symmetric thresholds.