Fix brightness for 72x40 display (#141)

Add a new command.
Add SSD1306B datasheet.

Author: ew1abz

CHANGELOG.md

@@ -8,6 +8,7 @@
 
 ### Changed
 
+- [#141](https://github.com/jamwaffles/ssd1306/pull/141) Brightness for 72x40 display.
 - **(breaking)** [#139] Removed default display size type parameters.
 
 ## [0.4.1] - 2020-12-01

doc/SSD1306B_rev1.1.pdf

@@ -86,6 +86,8 @@ pub enum Command {
     Noop,
     /// Enable charge pump
     ChargePump(bool),
+    /// Select external or internal I REF. Only for 72 x 40 display with SSD1306B driver
+    InternalIref(bool, bool),
 }
 
 impl Command {
@@ -160,6 +162,18 @@ impl Command {
             Command::VcomhDeselect(level) => ([0xDB, (level as u8) << 4, 0, 0, 0, 0, 0], 2),
             Command::Noop => ([0xE3, 0, 0, 0, 0, 0, 0], 1),
             Command::ChargePump(en) => ([0x8D, 0x10 | ((en as u8) << 2), 0, 0, 0, 0, 0], 2),
+            Command::InternalIref(en, current) => (
+                [
+                    0xAD,
+                    ((current as u8) << 5) | ((en as u8) << 4),
+                    0,
+                    0,
+                    0,
+                    0,
+                    0,
+                ],
+                2,
+            ),
         };
 
         // Send command over the interface

src/command.rs

@@ -28,9 +28,10 @@ pub trait DisplaySize {
     /// width * height / 8
     type BufferSize: ArrayLength<u8>;
 
-    /// Send resolution-dependent configuration to the display
+    /// Send resolution and model-dependent configuration to the display
     ///
     /// See [`Command::ComPinConfig`](../command/enum.Command.html#variant.ComPinConfig)
+    /// and [`Command::InternalIref`](../command/enum.Command.html#variant.InternalIref)
     /// for more information
     fn configure(&self, iface: &mut impl WriteOnlyDataCommand) -> Result<(), DisplayError>;
 }
@@ -85,7 +86,8 @@ impl DisplaySize for DisplaySize72x40 {
     type BufferSize = U360;
 
     fn configure(&self, iface: &mut impl WriteOnlyDataCommand) -> Result<(), DisplayError> {
-        Command::ComPinConfig(true, false).send(iface)
+        Command::ComPinConfig(true, false).send(iface)?;
+        Command::InternalIref(true, true).send(iface)
     }
 }