Update README.md

Adding examples for environmental sensing

README.md

@@ -1835,6 +1835,48 @@ A registry allows you to publish your Rust libraries as crate packages, to share
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 * [w4/chartered](https://github.com/w4/chartered) - A private, authenticated, permissioned Cargo registry [![CI](https://github.com/w4/chartered/actions/workflows/ci.yml/badge.svg)](https://github.com/w4/chartered/actions/workflows/ci.yml)
 
+## Enviornmental Sensing
+
+- **[Sensing Variable capacitance changes like Water level changes with Single Pin and resistor](ex-gpio-change-pin-direction-var-cap-read-1-pin)
+  Charges a variable capacitor towards VCC and measures time to for voltage to drop to logic low transition level while using only 1 pin
+  and 1 resistor. A good  way to add touch or poximity sensing to any CPU that has a spare I/O pin. It Demonstrates the following: *esp-idf-hal*
+    - Change GPIO Pin Direction
+    - Read GPIO Status
+    - Mesure variable capacitance
+    - Using Polling to detect GPIO status change
+    - Measure elapsed time in Microseconds(uS)
+    - Measure elapsed time in Nanosecods
+    - Delay for Micro seconds and milli seconds    
+    - Disable debug logging
+    - Isolate pin Assignments for each change between boards
+    - Change default watchdog timer in default.config
+    - Change minimum freetos task sleep down to 1ms
+
+- **[Sensing Variable Capacitance with 2 pins one of which must be High Drive Open drain ](ex-gpio-measure-time-to-change-high-to-low)**
+  This project aims to measure changes in capacitance using a foil strip sensor taped to a bottle. The idea is to track the time it
+  takes for a circuit to charge from 0V to a logic high transition voltage around 0.7V.The theory is that a higher capacitance, caused
+  by increased water level, should take longer to charge. Conversely, a lower capacitance due to decreased water level should charge faster.
+  An advantage of this circuit is the high drive pin can drain the capacitor very fast which means the circuit can cycle fast.*uses esp-idf-hal* 
+    - Measure elapsed time    
+    - Detect change in GPIO state
+    - Demonstrate Open Drain high-impedance pins 
+    - Delay for a specific duration
+    - Change OpenDrive GPIO pin mode between Drain and high impedance
+    - Oversampling to improve reading stability 
+
+  **[RS485 Read/Write with 1/2 Duplex transceiver](ex-uart-echo-rs485/readme.md)**: Reads uart 1 byte
+  at a time and writing data back to sender 1 byte at a time with write enable
+  pin control to allow use of 1/2 duplex transceiver.  RS485 is heavily used in enviornmental
+  sensing especially when we need to deliver data several hundred feet through metal rich soil *esp-hal*
+
+- **[UART - Process inbound uart data while also doing other work](ex-uart-non-block-rs485/readme.md)**:
+  Include code that shows how to control Write Enable pin for 1/2 duplex RS485
+  transceiver.   The Real value in this example is showing how to use non-blocking
+  fast polling to accomplish what is normally done with async threads.  In some instances the
+  fast polling can deliver more predictable results since you have more control over which
+  code is receiving time slices than you do with threading.  *esp-idf-hal*
+
+  
 ## Resources
 
 * Benchmarks