Yeah, you could even do an analog modular-style patch bay with all the gpio's, with one or multiple axoloti core's. All gpio's are 3.3V, so that's ok if you only connect 3.3V sources.
I suggest a 220Ohm resistor in series between VDD and jack for expression pedal input, to avoid shorting VDD.
Ok, so this is great news.
I just wanted a confirmation, so I sketched up using mono jack and stereo.
Can I just use mono jacks for analog out and in, or do I need to wire it up the stereo way ? (which works well with my expression pedal, thanks for telling me to add a resistor).
The switch and pot was just for me for giving a maximum of modularity to the thing,
I suppose I could always have a 3 way switch and have all 3 configurations possible, one for expression pedals, light / distance sensors, (with a stereo jack), one for sustain pedals, triggers, digital out (led or other) and a pot or a button (in case you don't want to plug anything in)
Looks fine. One extra trick could be using a jack with built-in switch(es), so the pot is connected when there is no jack inserted. Then you do not need an external switch.
Sorry, I'm still trying to understand.
If I put 2 stereo jack plugs on 2 different axoloti boards, Then use a stereo jack to plug them together (for analog transmission) don't I have a problem with both VDD being connected together (with a 440ohm resistance between the two) ?
Hello Paul,
I'm not sure if your drawing is referencing an older version of the board or not. I have a Axoloti Core V 1.0, and several of the pinouts are different from your wonderful drawing.
I've attached a red-lined drawing that shows the pinouts that are different. If you have an illustrator/eps/pdf/svg file, I'd be happy to make modifications to the drawing, if you like.
Regardless, thank you for the the drawing, it really helped solidify the functionality in my mind.
thank you Dazzling Duke. You spotted a big error. I corrected the wrong pin outs and upload the original illustrator file to github for further modification.
Download: illustrator file
Hello mtyas,
Finally did you wire that way, with a 220ohm resistance between VDD and jack? Did you use mono or stereo Jack for communication between Axolotis? And did you tried the jack with built-in switch? I guess it works since I saw your videos (exciting 3 Axolotis plugged together).
Thank you
Yes to all questions. Stereo jacks, resistors on all jack sockets and I used jacks with built in switches.
It all works really well
I actually also put mono jacks (with switches) before some of my buttons, so that I can send or receive trigger signals. But I connected them to the GND and the Gpio's instead of VDD and Gpio (giving me more connection possibilities, like sticking a led onto a jack)
Does anybody know if Doepfer modulation wheel kit can be plugged anywhere in the Gpio?
http://www.doepfer.de/zubeh_e.htm
And Yamaha BC2 breath controller?
http://usa.yamaha.com/products/music-production/accessories/breathcontrollers/bc2/
There is very few informations about specs in that previous link. Maybe more info here, page 8:
http://www.doepfer.de/pdf/WE_Manual.pdf
I read 5v and I think it should be 3,3v... Is there any risk of damage to the Axoloti in case of wrong potentiometer voltage?
Thank you very much
The Doepfer mod wheel kit can be connected similar as the Potentiometer in the diagram top left here: https://sebiik.github.io/community.axoloti.com.backup/t/official-pin-out-ports-documentation/202/11
Not all gpios are suitable, only the one's capable of analog in.
Just use VDDA (3.3V) where Doepfer says to use 5V. Resistive dividers behave proportionally.
If you do not connect anything to the 5V solder pad, and do not involve an extra power supply, so only involving gnd, vdd, and gpio, it'd be hard to damage the gpio's.
I have heard evidence of the gpio's surviving exposure to 5V, but it is out of spec.
I have no experience with breath controllers, the situation is a bit different since there is active electronics inside, and seems to need a power supply of 12VDC.
here's some discussion:
http://www.eevblog.com/forum/projects/breath-controller-for-synths-w-bc-input-need-design-help/
Thank you very much Johanes, first of all, for your incredible project, and for the time you spend helping us. Thank you for that information about Breath Controller. No I understand why it only works if supported by the gear. There are a lot of other interesting things to do with the Axoloti Gpio. I'll try to understand really how it works... it's a good thing is there isn't damage risk; it's an invitation to experiment.
And thank you Mtyas, I'll try the same double connections.
Connecting the VDD's of two boards would not so much be an issue. The real issue is hotplugging the jacks if there would not be a resistor limiting the current. When you insert a jack, the tip of the jack (VDD) will connect to sleeve (GND) of the socket. I would not expect permanent failures caused by that, but it is going to reset the processor for sure...
hello every one please excuse my newbie questions, I'm new to diy electronics however have been working with synthesis and music for over 12 years. I'm wanting to hook my axoloti up to a eurorack. I'm a little confused about what vdd is and what vda is. I know to amplify the signal to 0-5 volts I would want to use an op amp feeding back into the the inverting input with some resistors but that's about as far as I can figure. I would then run that output to the jack and also attach a ground. I've seen the diagrams for scaling cv down. Something similar to help amplify it would be useful.
Ok I've been doing some research and this is what I've come up with where R(f) = 13.7K, R(g) = 26.7K also you would want to add a 100K across the input: a) so with nothing
plugged in you get zero out, and b) for some level of ESD protection. And i guess the ground from axoloti and eurorack need to be tied together.
So, judging from the circuit, you want to convert 0-3.3V from the axoloti to 0-5V. I don't think 5V is the most obvious voltage to feed to eurorack, but it is a possibility (eurorack range is -12V to +12V, so anything in between that is a valid control voltage). For "digital" (trigger and gate) signals 5V is reasonable (will trigger most modules), but 12V is also fine (will trigger all modules), and even 3.3V should trigger many modules.
Anyway, some tips:
- The circuit you show is a non-inverting amplifier with a gain of (1 + Rf/Rg) = 1.5 (about)
- Probably no need to try to get exactly 5V out, why not use common resistor values.
- Putting 100k from Vin to ground indeed makes zero out when nothing is plugged in, but it doesn't provide any meaningful input protection. You could add a series resistor of 10k or so before just before the opamp input, depending on which opamp you use that may be good protection.
I don't really know very much at all. I was thinking I would try something simple to start. some -5 to 5 volts would be ideal for needs. many eurorack modules clip after five volts and can't tolerate anything over 10. 5 volts is pretty common to open a gate these days. how much harder would it be to make a circuit that didn't just amplify but added negative offset to get that -5 to 5 voltage?
Reading back my previous post sounded maybe a bit inpolite, sorry about that!
Yes, you can add an offset voltage quite easily. Here is an example that doesn't give exactly 5V, but close enough using standard resistor values:
The 3.3V reference is from the axoloti, and Vin also comes from an axoloti output. The opamp should be powered from eurorack +12V and -12V, such that it can provide positive and negative output. Almost any opamp can be used, for example TL07x or LM358/LM324 are cheap and good enough.
awesome! I am 100% new to circuitry and have only been able to understand and read circuit diagrams for about the last week. so a big thanks to the axoloti community and Johnannes for helping to push me out of my comfort zone. I have those specific resistors on the way plus just a general pack of about 10 different common resistors, I think I should have the values on that diagram and will definitely give your circuit a go once my breadboard gets here. as far as OP amps go i've got some tl072s on the way! @kassu thanks for tyhe diagram soooo helpful... if you've got a chance and could do one for the other way to go from eurorack to axoloti that would be amazing, there is a diagram over on the euxoloti thread however I got confused with there being two different diagrams and unclear labeling of the value of the resistors. I figured I'd start going out as it seems less risky of damaging anything than going into the axoloti from eurorack.
There are several ways to do the input, indeed one has to be careful to protect the axoloti from damage. The euxoloti design uses external ADCs as extra protection (they are cheaper to replace than the axoloti), but the analog circuit from there can be used also directly. Here is a slightly modified version:
I changed it to use the -12V reference voltage from eurorack. It has the transfer function:
Vout = - (33/100)Vin + (33/240)12V
Note that it is inverting! But that is easy to correct in the axoloti patch.
Important point is that it relies on the opamp to clip the voltage to 0-3.3V, and it needs a special "rail-to-rail" opamp which is powered from 0V and 3.3V. To use TL072 a different circuit is needed, maybe I get around to posting an idea later.
I added R9 to limit the current that can flow into/out of the axoloti pin in case something goes wrong with the voltage clipping. This then uses the internal protection diodes of the axoloti chip. The datasheet says you can put 50kOhm max without reducing the accuracy.
Thank you! I can't seem to find the Mcp400x I saw some Ada op amps that were rail to rail but I have no idea about appropriate frequency and slew and all that. Perhaps you could suggest another? What do you think about diodes? Does axoloti have some on the board? I have seen diodes used pretty frequently in a circuit for the ns1 like this http://www.sound-machines.it/product/ns1nanobridge/ in fact I wonder if plugging in the axolotis 3.3v and ground instead of the ns1 5v and ground would make it usable with the axoloti. I wish I could find a circuit diagram for that I have a feeling it make be using a circuit similar to yours. If this could be used with axoloti that would be awesome. If not I will be working on making my own. First on a breadboard. This is super exciting for me. I'm also planning on trying to breadboard a simple lfo with some of the parts I got coming.
