I’ve been doing some experiments with using the Arduino Nano as basis for a little banana sequencer, which I would like to use with my 73-75 Voice. So far I figured out that the Nano’s digital outs can be used as triggers and the PWM outputs (with some limitations) for CV. But before doing some further experiments or even moving beyond the breadboard, there are some basic (electronics beginner’s) questions that maybe some of you can help me with:
The Arduino Nano’s maximum output voltage is 5V, so that’s safe with my Serge and probably most other banana gear. But what about the current? Could there be a scenario where a CV input will draw more current than the Arduino can provide? What would be the worst case result here and are there some simple protection techniques?
The Arduino only outputs positive voltage and I’m not going to have it receive any input from the synth (for now). However, would it still be a good idea to put something like a protective diode before the output, just to make sure nothing goes wrong when accidentaly plugging the Arduino’s/sequencer’s out into an out of the synth?
And apart from that, are there some other precautions that should be taken care of?
I think @mzero has been working on something similar to interface with Serge and might have some ideas.
I would use a simple op-amp buffer between the Arduino outs and the banana outs.
Then the current will be drawn from the op-amp, rather than the Arduino.
You could also amplify the 5v from the Arduino to 8v for the Serge. (I think Serge CVs are 8v, but I don’t own one so I’m just half remembering things!)
I did recently design and build a clocking module that works with both banana jack gear (Serge tested as I have one, C-L should work… but awaiting a user to tell me so) - and the alligator patch points of Pulsar-23. It’s open hardware and open software: https://github.com/mzero/pulsar-buddy/wiki
Indeed, you should have protection, because someone (like, say, me) is going to accidentally mis-plug a hot output into your circuit and fry your Arduino if you are not careful … One of the lessons from my first prototype!
Current should not be an issue: Modular inputs are high impedance. They are sensing the voltage level, then don’t need (or want) to be driven by the current. Just have an output resistor (1kΩ) to ensure there is always some resistance.
However - what @barrford suggested is another way to go: If you want a wider range of CV, then you need to either have an op-amp (which will ensure micro current from the Arudino), or a transistor (what I did) to boost the signal level up. Of course, this in turn raises power supply needs: For an op-amp you generally need both pos. and neg. supplies (some need only pos. and gnd… but then the amplification is around half +V… which can be awkward and has its own design problems).
I’m actually pretty new to circuit design here myself - just about 6 months into it… but happy to help - DM me if you want to chat (text / audio / video) - and/or look at schematics.
Thanks a lot for the good advice, these are some very good starting points for further experimentation!
I also found this article very interesting, it’s a very helpful comparison between regular diodes and Schottky diodes for reverse polarity protection.