--- a/FC-handset-spec	Tue Jun 15 22:58:06 2021 +0000
+++ b/FC-handset-spec	Sat Jul 03 07:01:39 2021 +0000
@@ -91,9 +91,8 @@
 
 1.4.2. Specific LCD module selection
 
-As of this writing, the specific LCD module to be used has not been firmly
-selected yet.  We are actively looking for an LCD module that fits all of the
-following requirements:
+As of 2021-07, the frontrunner candidate LCD module for our FC handset is
+Formike KWH020ST23-F01.  Our selection criteria are as follows:
 
 * TFT color LCD, 2.0" diagonal, 176x220 pixel resolution;
 
@@ -116,6 +115,13 @@
 backlight LED wiring requirement stems from the constraints of our chosen
 MAX1916 backlight LED driver chip - see section 1.4.4.
 
+Formike KWH020ST23-F01 is an LCD module that was discovered by Mother Mychaela
+in May-June of 2021, and it appears to satisfy all of our requirements.  We have
+designed a test board for the purpose of evaluating this LCD (it will connect
+the new LCD to our Luna interface from 2020), but because of Digi-Key part
+backorder issues, the assembly of this board and thus the actual test are being
+delayed until Sep-Oct of 2021.
+
 1.4.3. Backlight and readability considerations
 
 Out of the various pre-existing mobile phones which I (Mychaela) have
@@ -175,16 +181,16 @@
 instead of 30 s), the display goes dim instead of fully off, and in this dimmed
 (but still readable) state keypresses are NOT swallowed.
 
-We only need to implement two different intensity levels for the LCD backlight:
-full brightness and in-call dimmed.  The backlight intensity level in the dimmed
-state will need to be chosen on this principle: use the lowest backlight LED
-current (to conserve battery power and allow longest talk time on one charge) at
-which the display is still readable, similarly to Pirelli's in-call dimmed
-state.
-
-In the user-actively-poking state, as opposed to the long-call dimmed state,
-there is no need to provide different configurable backlight levels - see
-section 1.4.5.
+In terms of absolute requirements, we only need to implement two different
+intensity levels for the LCD backlight: full brightness and in-call dimmed.
+The backlight intensity level in the dimmed state will need to be chosen on
+this principle: use the lowest backlight LED current (to conserve battery power
+and allow longest talk time on one charge) at which the display is still
+readable, similarly to Pirelli's in-call dimmed state.  In the user-actively-
+poking state, as opposed to the long-call dimmed state, there is no strict need
+to provide different configurable backlight levels - but it so happens that our
+implementation will allow a total of 4 different backlight intensity levels -
+see section 1.4.4.1.
 
 1.4.4. Backlight circuit implementation
 
@@ -244,14 +250,14 @@
 The special quality of MAX1916 is that it produces constant current through each
 LED (based on a set reference current and 230x current multiplication circuit
 inside the chip) regardless of variations in both Vbat and Vf!  Of course the
-requested current can only be sustained as long as Vbat >= Vf + Vds, where Vds
-is the lowest drop voltage of the FETs inside MAX1916, and once Vbat falls below
-this point, the LED current will begin to decline.  However, the beauty of this
-design is that no arbitrary artificial turnover points (like the 3.5 V point in
-our hacky design from the spring of 2020) need to be set: the battery discharge
-point at which the LED current begins to decline will be whatever it comes to be
-naturally, based on Vf (perhaps depending on temperature) and MAX1916 Vds, and
-the decline is expected to be gradual.
+requested current can only be sustained as long as Vbat >= Vf + Vds_min, where
+Vds_min is the lowest drop voltage of the FETs inside MAX1916, and once Vbat
+falls below this point, the LED current will begin to decline.  However, the
+beauty of this design is that no arbitrary artificial turnover points (like the
+3.5 V point in our hacky design from the spring of 2020) need to be set: the
+battery discharge point at which the LED current begins to decline will be
+whatever it comes to be naturally, based on Vf (perhaps depending on
+temperature) and MAX1916 Vds_min, and the decline is expected to be gradual.
 
 1.4.4.1. Backlight current selection and dimming
 
@@ -267,13 +273,20 @@
 buffer's A input will be tied high, and the two Calypso GPIO outputs will be
 connected to buffer output enable inputs.  There will be two resistors with
 different carefully computed values, each connected between one of the two
-tristate buffer outputs and MAX1916 SET pin.  One resistor will provide a small
-current, the other will provide a large current, and each of these two currents
-will be switchable on/off by Calypso GPIO signals switching the buffer outputs
-between driving high (2.7-2.8 V) and Hi-Z.  Resistor values will be chosen such
-that the sum of both currents will be the 15 mA limit (the current is reckoned
-per LED), whereas the small current alone will be whatever we need for the
-battery-saving long-call dimmed mode.
+tristate buffer outputs and MAX1916 SET pin.  There will also be a third
+resistor connected between MAX1916 SET pin and the V-IO rail.
+
+The values of the 3 just-described resistors will be selected so that the path
+through each SET resistor will add a different contribution to the total LED
+current.  The always-on SET resistor will provide the smallest current
+corresponding to the long-call dimmed mode, whereas the sum of all 3
+contribution currents will equal the 15 mA limit - the current is reckoned per
+LED.  The difference between the 15 mA maximum and the small dimmed mode current
+will be split unequally between the two switched SET resistors, allowing a total
+of 4 different backlight intensity levels to be selected via the two Calypso
+GPIO outputs going to the 74LVC2G125 buffer's output enable inputs.  The actual
+currents will be determined some time around Sep-Oct of 2021 when we get our
+lunalcd2 test board built.
 
 1.4.5. Slight regression relative to Pirelli DP-L10
 
@@ -284,7 +297,7 @@
 backlight intensity increases with more 0s being put out on PWL, as opposed to
 more 1s.  Thus regardless of the unknown actual circuit implementation, the
 backlight intensity appears to be continuously variable from 1/255 to 255/255,
-which is certainly a much richer control than our crude selection of just 3
+which is certainly a much richer control than our crude selection of just 4
 possible LED currents.
 
 In terms of what Pirelli's fw offers to end users, the backlight intensity in
@@ -1358,10 +1371,18 @@
 
 3.5. LCD module and backlight
 
-It is the Mother's desire to finalize the selection of LCD module for the actual
-handset before embarking on the detailed design (as in schematics, BOM and
-layout) of FC Venus, and to implement the final LCD and the final backlight
-circuit on the Venus board.
+The Mother's original intent was to finalize the selection of LCD module for the
+actual handset before embarking on the detailed design (as in schematics, BOM
+and layout) of FC Venus, and to implement the final LCD and the final backlight
+circuit on the Venus board.  However, because of the delay in KWH020ST23-F01 LCD
+testing caused by Digi-Key part backorder issues (see section 1.4.2), this plan
+is being modified slightly: the design of FC Venus board is being ungated on the
+bet that KWH020ST23-F01 LCD module will pass all necessary qualification tests,
+but this Venus board design won't be sent out to PCB fab until those LCD tests
+actually pass.
+
+The backlight circuit design of section 1.4.4.1, which is hoped to be final, is
+being included in the Venus board design.
 
 3.6. Keypad buttons