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Here's the first pass of the schematic. I still have to add the AC244 and its' associated connector.
I'll do that over the weekend. It'll give me a chance to redo the AC238 outputs (I'm not too keen on the way they look.)
Next week, I'll pick up a display unit and set up the SPI interface to the display.
The final schematic will be done in Kicad. Then, I can generate the necessary files for making a PC board.
MJ .. You must be eating your meals at the work bench you seem to have MiDi well under control.. Hope the PIC's 32k Flash is enough... as a side issue...If you have a spare IO , for a prototype I put a Led on a pin that flashes at startup so I know the 'beast' is running... LCD, writing to this display may eat up into your scan uSecs.
@wkrug,granddad: Thanks for the compliment. I'm a New Yorker. We're always pushed into getting everything done "yesterday".
wkrug: I was looking at displays and the one I picked from Mouser seemed to be the best compromise.
The cheapest and the most readily available.
Pommie: As far as what scan time will produce a specific velocity, I'm not sure.
Typically, the keybed scan rate is around 2000Hz. That seems to be what everybody else is doing. (Roland, et.al.)
I'm guessing that the geometry of the actual key switch seems to be a standard that was established by Fatar.
Once I get the system up and running, I'll hook a Logic Analyzer up to the pins and see. I'll post pics here.
Something just dawned on me. If I add one more AC573 and one more OE strobe, I can make this board handle keybeds of up to 88 keys.
You can put an DSO at the 2 sample lines ( or a logic analyzer ), when pressing a key.
The diode lines can be set to a fix potetial.
Then press a key once hard as You playing and once super soft.
So You get 2 reaction times, between the 2 contacts that will give You the span of useable velocity.
When start the keyscan via timer in CTC Mode You can change the scan time very easy, only by changing one value ( Comparematch Value ). Terminology is from AVR - In PIC the functions are possibly named different.
This is the latest firmware for the keytar project. It was built using MPLAB-X version 5.1 and the XC16 Assembler.
It is designed to go with the schematic diagram in post #143
This post will be updated as I update source code.
There's still a lot to do. I need to set up and test the A/D convertors, as well as the UART settings.
Then, the SPI display needs to be made working. For that, I have some time because I haven't ordered the display yet.
If you see something that doesn't look right or have some suggestions, please post a reply here.
I'm releasing this source to the public domain, with the proviso that you agree to indemnify me and hold me harmless
for any problems or issues that you may have using this source code.
Use it at your own risk and peril.
And please! Be sure to mention this forum if you're asked where it came from.
The folks here have been very kind and helpful. They give freely and ask for nothing in return.