ESP-01 as Access Point + Arduino Uno R3 + Android

I followed the tutorial at add-wifi-to-arduino-uno. The article has several errors with the major ones being the schematic and not enabling DHCP mode when the ESP-01 is set to be an Access Point.

The ESP-01 should have 10Kohm pull-up resistors as shown on the schematic at flashing-the-ESP-01-firmware-to-SDK-v2.0.0-is-easier-now.

The ESP-01 requires adequate 3.3V power and should not depend on the Arduino Uno's 3.3V pin.

I modified the author's Arduino program by replacing String objects with char arrays which is more appropriate for the Arduino's limited memory.

Use TCP Client app by MightIT from Google Play Store to send commands to the Arduino Uno.
Use the Arduino IDE's Serial Monitor to send AT commands to the ESP-01.

Arduino Uno R3 + 433 MHz + Bluetooth + Android

The Bluetooth module is a HC-05 revision GW-040 which appears to be very similar to the ZS-040.

Using the Bluetooth Terminal app on an Android smartphone, messages are sent to the HC-05. That message is received by the HC-05 and passed to the 433 MHz transmitter module which sends it.

Arduino Nano + 433 MHz + LCD

The 433 MHz receiver module receives messages from the 433 MHz transmitter module controlled by the Arduino Uno in the circuit above.

The messages are displayed on the LCD. In addition, if the message is 1rr, the green LED turns on. If the message is 1yy, the yellow LED turns on.

The 433 MHz receiver module has the SYN480R chip. The 433 MHz transmitter module has the SYN115 chip.

The LCD display is 16x2 using the HD44780 display controller/driver.

Web Server example sketch

The Web Server example sketch included with the Arduino Ethernet library that is installed by default with the Arduino IDE 1.6.7 works only for GET http requests. I modified the sketch for POST http requests.

The original sketch stops reading when the an empty line is received which works for a GET http request message. The initial http request message from a web browser to the Arduino Ethernet Shield IP address is a GET http request message. When the webpage sends a POST http request message, there is an empty line which separates the header from the body. The body contains the POST data. The new sketch looks for POST http request and keeps reading.