Hello everyone, I am working on a music project that uses Arduino to allow me to turn data from music software called ‘Pure Data’ into voltage, that can then be used to modulate a modular synth. I know next to nothing about electronics and Arduino, so I have certainly bitten off more than I can chew by myself, and I intend to go back to the start once this is all over to learn from scratch in a traditional way, but this project is very exciting to me so I wanted to throw myself in and learn the hard way.
After a lot of trials and tribulations, I now have 8 3.5mm mini jacks that can output 0-5v that I can modulate manually or automate with Pure Data we which is very cool, but the next step in the project is more complicated than what I have faced so far: I need to output -/+5v from each minijack. I know so little about electronics that I don’t even know for sure the term for this - bipolar I think?
My Google searches are maybe not the best because my electronics vocabulary is poor, but from what I gather, most people with similar problems are advised to use an op-amp. However, in most cases that I find the person asking the question is content with that answer - being told op-amp is enough for them to go ahead and get on with their project, so the trail stops there.
Here are my questions:
Looking at my project, is an op-amp the way to get from 0-5v to +/-5v? Or is there another method?
If op-amp is the way to go, can anyone advise an actual model?
Would I need an op-amp for every minijack? (8 op-amps)
I apologise for the diagram that I have made, I hope that it is understandable. I tried to photograph the breadboard but it looks like a mess of cables, and I don’t know enough about electronics diagrams to do it the proper way.
It's for Eurorack modular synthesizer (Eurorack - Wikipedia). There's not really a standard voltage range for bipolar CV from what I can gather, but I've gone through the manuals of the modules I own and +/-5v seems to be what I would get most mileage out of.
The voltage allows you to control things like amplitude, or scan through/jump around a sample, or output an LFO, or an envelope, etc, depending on the module.
Well you need to go from 0-5 to +/-5. that's from a 5V p-p signal to a 10V p-p signal so some sort of amplification is needed. An op-amp may be the best solution.
Would I need an op-amp for every minijack? (8 op-amps)
If you use an op-amp, yes.
If op-amp is the way to go, can anyone advise an actual model?
What will be connected to the output of these amplifiers?
I'm really very new to this so I've only used a breadboard to date. My hope was to get the concept working on a breadboard and then the next step in the project would be how to make it into a neat and tidy board that is housed in a nice box of some sort. The size of that part you linked is attractive if I have to use 8 of them though.
I don't want to limit my choices but I don't think I would trust myself to get a printed board produced without seeing the concept work with my own hands and multimetre for real first. Am I creating problems for myself?
I thought of that too. It generates its own voltages, and it's fine with short circuits. I stopped looking at it when I went through the datasheet and saw that on a 5V supply their RS232 voltage swing is typically +/- 8V. So close. Maybe there's some way to limit the output swing?
The MAX232 is an RS232 line driver. I don't see how it could be useful.
I thought your signals were analog, like sinewaves, sawtooth, music, etc. Is that true or not?
If true, are you still interested in an op-amp solution?
The signals I want to output are just voltage, Control Voltage (CV) I think is the technical term form this application, no waves or audio or anything like that.
As an example, one Eurorack module could be a sample player that has 3.5mm jack inputs that allow you to modulate certain things such as the playback speed (depending on the design of the module). The voltage range that it expects would be +/-5v. If I send -5 volts the playback would be reversed at 4x speed, 0 volts the playback is stalled, +5 volts the playback is at 4x speed forward. But the audio is hosted in the Eurorack module itself, I'm only trying to control/modulate the parameters via voltage ( via my computer and Arduino).
Same goes for sinewaves etc: I have a Eurorack oscillator module, and through control voltage I would be able to modulate the pitch for example, but the oscillator itself and the output audio is all contained in the Eurorack module.
