LED power board improvements, per issue #42

* Increased thermal relief
* Moved C10 well away from J9
* R24 and R9 are now the same value, 3.6kohm
* Removed R0
* Removed the need for the +15V supply with an LM317.
* Removed I2C IO expander and replaced with an STM32G0

hardware/led-power/README.md

@@ -1,35 +1,8 @@
 # LED Power board
 
-As covered in the main design doc, the board takes +15V and +48V,
-and uses them to feed 8 strings of LEDs with a constant current of
-~20mA.
-
-# FAQs
-
-* Why do we require a +15V supply?
-  * A low power DIN rail +15V supply is <$10. An on-board regulator
-    that could regulate the +48V down to +15V, without getting too hot,
-    would cost about the same amount. There are cheaper regulators that
-    could produce +5V, but we need to provide the op amps with something
-    higher.
-* The +15V supply is really kind of dumb, we're only drawing about 100mA.
-  * Yes, and the op amps can run off of 45V. I'm considering a new
-    version which runs off a single ~40V supply. But 40V supplies don't
-    fall off of trees. So it isn't an obvious win.
+As covered in the main design doc, the board takes +48V, and uses them
+to feed 8 strings of LEDs with a constant current of ~20mA.
 
 # Design
 
-## Constant current regulation
-
-We've got a chain of ~22+1 LEDs, which will have a combined forward voltage
-of between 30V and 37V, depending on part variation and current conditions.
-We'd like to apply a constant 20mA to them. We've got a ~48V supply to work
-with. The suggested supply is actually a 43V to 52V device. So we need to
-be able to drop anywhere between 23V and 6V, while controlling the current.
-
-To do this, we stack an N-channel MOSFET on top of a temperature
-stable precision resistor.  The precision resistor is chosen so that
-when we hold a certain fixed voltage across the resistor, 20mA is
-developed through it. To hold that voltage, an op amp drives the MOSFET's
-gate to whatever voltage is necessary for the MOSFET's resistance to
-drop the excess voltage.
+See [the wiki page about the board](https://github.com/jkominek/piano-conversion/wiki/LED-Power-Board) for details on how it works.

hardware/led-power/fp-lib-table

@@ -1,3 +1,3 @@
-(fp_lib_table
-  (lib (name footprints)(type KiCad)(uri "C:/Users/Jay Kominek/Dropbox/Piano Conversion/footprints.pretty")(options "")(descr ""))
-)
+(fp_lib_table
+  (lib (name "footprints")(type "KiCad")(uri "${KIPRJMOD}/../footprints.pretty")(options "")(descr ""))
+)