Official pin out/ports documentation

mtyas 2016-06-16 08:55:08 UTC #79

I've put jack inputs on most of my GPIO's, and I was wondering if I could have a multicord jack to patch one analog output into multiple analog inputs ?

Would it divide the voltages, or use too much power, or do something that shouldn't be done ?

If it is possible, couldn't I make a simple kind of dispatch-box, and maybe insert some kind of pot / variator on each output (so that I could dose the full PA4 range into all the different inputs) ? I don't know anything about electronics, so it's probably a silly question

johannes 2016-06-18 12:47:20 UTC #80

That looks great to me!
The 220ohm resistors won't divide unless you connect two outputs together, in other cases they will limit the current to a reasonable value, that's a good thing because when inserting a jack, the tip (signal) briefly touches ground, without resistor that could cause glitches.

johannes 2016-06-18 19:44:56 UTC #81

A few second thoughts:

if I understood correctly, you plan to integrate the resistors in the patch cords? This is possible, and quarter inch jacks often have enough space inside. But wouldn't it be more convenient to mount them between gpio and the jack sockets?
The other concern is channel crosstalk, unconnected analog inputs track connected analog inputs quite a bit. To mute this effect, you could use jack sockets with a built-in switch (quite common), and use this switch to ground unconnected inputs. Or, without switching jacks, connect a 22kOhm resistor between gpio and ground (keep the 220 Ohm series resistor). That will become a voltage divider, but you'll still get 98% range.

MikkelM 2016-06-29 12:14:23 UTC #82

I want to scale the output from PA4 and PA5 to 0-5v, does anyone have a solution in their sleeve that I can 'borrow' and put on a quick breadboard. I am a software guy, not hardware.

Cheers

Illuminate 2016-07-07 16:10:21 UTC #83

Scroll up... However it does require a bi-polar power supply. I've decided to use my axoloti stand alone and so I'm gonna work on something using a rail to rail op-amp for this purpose. If anyone else
Has thoughts and wants to chime in that would be great. But I think just replacing the tl072 with a rail to rail op amp should more or less do the trick to run it off the axoloti 5v and ground?

MikkelM 2016-07-07 18:10:45 UTC #84

So the circuit from the 22 jan Will do the trick.

Illuminate 2016-07-07 19:12:39 UTC #85

With a bi polar power supply it sure will. I've bread boarded one. You just need to add some caps between the power rails and ground as close to the op amp as possible to de-couple the op amp. This is standard and you can read more on it on most op amp data sheets.

avantronica 2016-09-19 11:05:15 UTC #86

A quick question - it may seem obvious, but i'd like to check whilst placing an order for the board and some general parts - I was pondering the right count for pots, I will pick up maybe 8 10 or 12 50k linear pots (sized like the monotron ones), but then it struck me, the magic number, 16, that would have been ideal, perhaps for a step sequencer

Now, without extra hardware, are we really limited to 15 analog ins, just want to check, it seems like an awkward number ? Is 15 the max, any constraints I should be aware of before placing the order shortly, I'll likely opt for 12 failing that

johannes 2016-09-19 11:45:11 UTC #87

Practically, the number of available analog inputs is 15.

Technically, 16 is possible but requires quite some development. Currently channel 16 is used for board voltage measurement, while I believe it is possible (but only 100% sure after this is developed) to do both voltage measurement and an external 16th channel. referencing brief discussion here Sorry for the tease.

I'd suggest adding a rotary switch on a single analog input, say, for patch selection, if you go for 12 potentiometers, sketched here, and more discussion

thetechnobear 2016-09-19 13:42:26 UTC #88

Any disadvantage, except reduced sample rate, to not use a MCP3208 as described here , this Is what I have on my next shopping list

johannes 2016-09-19 15:00:48 UTC #89

The main disadvantage I believe, is that it requires the MCP3208 chip (...), occupies the SPI port on GPIO (could be useful for something else too), and requires a custom object.

avantronica 2016-09-19 17:58:26 UTC #90

Probably not, just didn't have time to research it ... rather than getting an order + sundry components I just ordered the board (to make sure I just did it) and I will work out what I want for flexibility in this round once I get my feet under the table - I have a few pots and switches lying around for now - I also wasn't sure if the mounting lugs of the through-board pots I saw would attach simply to regular project board - didn't look like it - I'll pick up chassis mounted ones to keep it simpler, but I now need to source knobs to suit and I like johannes' suggestion to incorporate a rotary switch anyway : )

To get me through in the short term I might go looking for a thread detailing offering up bi-directional control to a virtual potentiometer array in something like lemur - presuming the iPad cck talks nice and so on.

I'm pretty sure once I realise the potential of the various i/o strategies I may adapt my thinking

Sebo 2017-01-10 21:58:04 UTC #91

I want to use the diode clamp using BAT85, where is better to connect the 3.3V, to VDD, VDDA o VDDC?
Thank you.

johannes 2017-01-12 12:05:59 UTC #92

I assume you're talking about a diode clamp as described in this post? Best is to connect the diode clamp to VDD or VDDA, whichever most convenient, but not VDDC.

Sebo 2017-01-12 14:46:58 UTC #93

Hi, sorry for my bad english...
Yes, I was talking about the diode clamp described in that post. I used the same circuit for protecting Arduino inputs, and I was concerned about if the 3.3V source can take the overvoltage without burning something.
Thank you!!!

jfcharles 2017-09-12 18:47:09 UTC #94

Could you explain why you leave the digital input floating when you show how to connect the Switch? I thought the common way of connecting a switch would be to use a resistor (say, 10k) from the gpio digital input to GND. Any pros/cons? Thanks!

SmashedTransistors 2017-09-12 20:16:08 UTC #95

Hi @jfcharles

If you are referring to http://community.axoloti.com/t/official-pin-out-ports-documentation/202/11

You can see that there is a note "set mode to pull-down"

The microcontroller GPIOs already has internal pull-up and pull-down resistors that can be set by software.

jfcharles 2017-09-12 20:33:31 UTC #96

Yes, so the pulldown resistor is inside the micro controller (which is not possible on Arduino, that's what I was thinking about).
Thanks for the clarification!

SmashedTransistors 2017-09-12 20:36:11 UTC #97

I asked myself the same question the first time i saw the schematics

Blindsmyth 2019-03-07 14:38:39 UTC #98

Hi there I have a question regarding the 220ohm resistor and jacks for expression pedals:

I have two stereo jacks for expression pedals. Could I use one vdda pin for both? If so how do I do it with the resistors? Do I put on resistor after Vdda and then split to both jacks, or two resistors one for each?

I've tried both these options and never got it to work. I only got it to work when each jack had it's own Vdda pin with a 220 ohm resistor in between...