i didn't even knew that there was only one analog input in fact. i was gonna propose the idea to join together several arduino boards, to get more true analog inputs, but if there's only one, i'd need 48 ! and i suppose it's impossible anyway to make a network of arduino boards, working together.
The Uno has six pins you can use for analog inputs. However, behind the scenes, they all use the same hardware to do the A2D conversion. So the more you use, the less frequently you can read them. You could indeed set up a network of boards communicating over serial and get more A2D channels but it would probably be more cost effective to multiplex some external A2D hardware to get the number you need.
so there's no problems doing this right ?
Sounds OK to me.
what would be the latency from the moment i turn one knob from 0 to 10 ?
Let's assume
a) you get from 1 to 10 really fast
b) use AWOL's figure of ~200 samples per sec per input.
c) divide that by 2 to allow time to do other stuff (not really necessary but let's be conservative)
So we sample an input every 10mS, there's 48 so a complete loop takes 480mS. The worst case is of you turn a knob the instant following it being sampled. Then you have to wait 48 * 10mS for another sample. That's 480mS or nearly half a second. That's bordering on being noticeable for say a light switch but I would think it's OK for something like a volume knob and statistically the average time would be half that.
i suppose that a digital on/off information needs a few samples, right ?
Depends on the input type, a mechanical switch needs to be sampled a few times to make sure it really has changed state (look up "debouncing"), a clean digit input can simply be read once.
a potentiometer indicating a value to the arduino needs more samples, right ?
A single read is often good enough. That said it's common to average a few readings to "smooth" things out, especially with mechanical devices like a pot that can have wiper noise.
is it possible to have a little lcd screen or something, for each control
Yes, if you can afford 48 of them. You can also use LEDs. Controlling 48 LCDs would be a challenge that needed some thought. 96 7-segment LEDs (two for each value so 0-99 not 0-100) would be easy. There's a heck of a lot of wiring to do though.
Note that I am just talking about reading pots and displaying the results, I have no idea what is involved with your MIDI application.
Rob
thanks a lot guys !
i first had troubles to understand the process , the arduino reading several times per second each value of each input. it's very different from the use of potentiometers i do usualy.
now i'm ok, and someone linked this to me, very cool ! 48 inputs using only three of the six inputs ! so i may even use 96 analog inputs !
90 samples/sec is far enough for me. indeed, if it takes one second to me to turn the knob from zero to ten , well the value will be updated and read about 90 times during this second ! so it's totaly cool...
i'll start to experiment it little by little, and program it for six inputs first. i need to buy some shields.
thanks again ! wonderful forum !