incorporate review comments

- README.adoc
Clarify that the wavelength of the IR LED should be compatible with the
detector used;
Correct the number of jumper wires in the BOM.

- Wiring diagram
Use red wire for +3v3 and black for GND.

- Fritzing source file
Fix having added the wrong file.

- ir_loopback/ir_loopback.c
Correct typo in comment.

- nec_receive_library/nec_receive.pio
Amend comment to clarify that the provided 'init' function sets the
state machine clock divider relative to the system clock.
Amend comment to clarify that the 'init' function sets up the ISR as
described.

Author: martin

pio/ir_nec/README.adoc

@@ -8,9 +8,9 @@ The tasks of encoding and decoding the data are offloaded to the RP2040 PIO stat
 
 == Wiring information
 
-Connect GPIO 14 to the positive side ('anode') of an IR LED via a suitable series resistor e.g. 1.5k Ohms, and the negative side ('cathode') to ground.
+Connect GPIO 14 to the positive side ('anode') of an IR LED via a suitable series resistor e.g. 1.5k Ohms, and the negative side ('cathode') to ground. The wavelength of the LED is unlikely to be critical so long as it is compatible with your detector.
 
-Connect GPIO 15 to the output of a 3.3v IR detector such as the VS1838b, and wire the power connections of the detector to the 3v3 and ground. The program expects the decoder output to be low (logic '0') when a carrier is detected.
+Connect GPIO 15 to the output of a 3.3v IR detector such as the VS1838b, and wire the power connections of the detector to 3v3 and ground. The program expects the decoder output to be low (logic '0') when a carrier is detected.
 
 [[pio_ir_loopback_wiring]]
 [pdfwidth=75%]
@@ -53,5 +53,5 @@ nec_carrier_control.pio::: The PIO assembler code to transmit a complete frame.
 | Infra-Red LED | 1 | generic part
 | 1500 ohm resistor | 1 | generic part
 | Infra-Red Detector | 1 | generic part e.g. VS1838b
-| M/M Jumper wires | 3 | generic part
+| M/M Jumper wires | 5 | generic part
 |===

pio/ir_nec/ir_loopback/ir_loopback.c

@@ -13,7 +13,7 @@
 // Infrared loopback example ('NEC' format)
 //
 // Need to connect an IR LED to GPIO 14 via a suitable series resistor (e.g. 1.5k)
-// and an ective-low IR detector to GPIO 15 (e.g. VS1838b)
+// and an active-low IR detector to GPIO 15 (e.g. VS1838b)
 //
 // Output is sent to stdout
 

pio/ir_nec/nec_receive_library/nec_receive.pio

@@ -11,11 +11,13 @@
 ;
 ; The input pin should be connected to an IR detector with an 'active low' output.
 ;
-; This program expects there to be 10 state machine clock ticks per 'normal' 562.5us burst period,
-; in order to permit timely detection of start of a burst.
+; This program expects there to be 10 state machine clock ticks per 'normal' 562.5us burst period
+; in order to permit timely detection of start of a burst. The initailisation function below sets
+; the correct divisor to achive this relative to the system clock.
 ;
-; Frames consists of 32 bits sent least-siginificant bit first so the Input Shift Register should be
-; configured to shift right and autopush after 32 bits.
+; Within the 'NEC' protocol frames consists of 32 bits sent least-siginificant bit first; so the
+; Input Shift Register should be configured to shift right and autopush after 32 bits, as in the
+; initialisation function below.
 ;
 .define BURST_LOOP_COUNTER 30                   ; the detection threshold for a 'frame sync' burst
 .define BIT_SAMPLE_DELAY 15                     ; how long to wait after the end of the burst before sampling