Gert, thanks for hanging out on the forums and taking your time replying to what must be real simple questions. I feel like I'm asking Newton for help in basic algebra.
Gert van Loo wrote:Mostly you have to specify at what rate and with what accuracy you want to control you 88 motors.
Think about that very hard! It is crucial! It determines how fast, how often and how accurate you have
to control them. It defines 90% of the output circuit circuit and also defines if it can be done at all. (or NOT!)
Well... from what I read in the Gertboard user manual it says that that clock runs at around 12MHz. Does that mean that you can switch the GPIOs at a 12MHz frequency? If so, even if each output is multiplexed 8 ways, you're still at 1.5MHz which is extremely accurate. Really I just want to build a toy. Accuracy within a 10th of a second is probably the most I would tolerate, and anything more accurate than a 100th of a second is great but my ears won't hear it.
Gert van Loo wrote:Next: what kind of motors are you thinking off? You mention a piano so do you really need motors
(To play from PPP to FFF) or are mechanical on/off actuators good enough. (e.g. a tower with 88 bells)
I was using a piano as an example. I do want to play music, but I do not not necessarily need a full 88. Maybe a little xylophone, marimba, bells, jars of water, etc. The main point was how do you, with 12 pins, control more than 12 things.
On/off actuators will probably suffice, though I'd like to have 2 per note; one to strike the note and another to dampen it. No varying levels of volume.
Gert van Loo wrote:
What kind of power do you need to control 88 times: 6V at 250mA, 12V at 1A or 240V at 10A?
Absolutely no clue. I will get the help of someone more electrically inclined when the time comes. I mainly do software... that's about it.
Gert van Loo wrote:
I have to warn you: Linux is not very suited for real time tasks. So if you really want to play
music on a piano you are looking at something very complex.
You mentioned this before here: http://www.raspberrypi.org/archives/1734#comment-29464
So how would you overcome this? From what I read, the IO on the Gertboard is buffered. So would I use Linux on the RP to fill the Gertboard buffers which in then move the actuators?