Good to see progress on the thumb cluster. Looks nice.
![Thumbs up! :thumb:](https://cdn.geekhack.org/Smileys/solosmileys/thumbsup.gif)
For fun after reading the comment that the 74165 was not following the SPI rules (and my brain needing to do something else after being in openscad all day). Here is an autonomous schematic that is following the SPI rules (if all the components work like I think they do).
Show Image
What is he schematic circuit supposed to do? Is it a shift register array? Where are the IR LEDs? What are the five JFETs for?
@wolfv
I did take a look at your schematics. How did the experiments go thus far? Did you try it with the IR Leds already...
I only tested with two IR LEDs. "Strobe buffers" on 26 IR LEDs was not attempted.
All other elements in sr4_keys folder passed testing, including the two IR LEDs.
https://github.com/wolfv6/keybrd_DH/tree/master/examples/shiftRegs/sr4_keysI read some datasheets on "digital buffer", "buffer amplifier", and "Schmitt-trigger buffer" but don't understand enough electronics to figure out which one is suitable for strobing 26 IR LEDs simultaneously. Any EE out there care to advise us on which one to use?
The following two sections are from
https://github.com/wolfv6/keybrd_DH/blob/master/examples/shiftRegs/README.md# sr4_keys overview (this was tested on breadboard)
The right row has two photoInterrupt switches, which consist of an IR LED and photo transistor.
A 20mA Teensy pin strobes two IR LEDs.
(The 52-key PCB will use strobe buffers instead. Adding strobe buffers to the circuit does not affect the firmware.)
# Strobe buffer (this is the schematic in sr5_dodohand_PCB, not tested)
To achieve fast polling, 26 keys are strobed simultaneously.
By "strobe" I mean power to the IR LEDs is on for a short time while the shift registers read the photo transistors.
Strobing 26 IR LEDs simultaneously requires much current (high fan-out capability):
All the IR LEDs at DigiKey are at least 20mA.
IR LED forward voltage: typ. 1.2 at 20 mA
26 LEDs * 20 mA/(2 LEDs in series) = 260 mA
26 LEDs * 5 mA/(2 LEDs in series) = 65 mA
The dodohand_PCB schematic powers the IR LEDs with "strobe buffers".
Some strobe buffer candidates are:
* digital buffer
* buffer amplifier e.g. LMC7101
* Schmitt-trigger buffer
I don't understand enough electronics to know which strobe buffer would work.
Someone that understands electronics can can figure this out.