After drafting the basic features and taking community feedback over Reddit. I decided to move ahead with proposed design. Thanks for suggesting cheap CP2102 for USB-UART.

1. Atmega328P: +3.3V Power, 8MHz Clocked.
2. Power Supply: USB & DC Jack for Powering the board.
3. ESP-01 and Xbee Radio Connectors.
4. Sensors: I wanted to add one Analog and one digital sensor on board
5. GPIO/ Pinout: Analog-digital pins on both side of the board. Extra SPI & I2C pins.

Let's dive deep :

Power:

• LDOs
  • LM1117: +5V/1A.
  • SPX3819: +3.3V/500mA.

Sensors:

• DS18B20 [Digital]:
  • Popular One-Wire Digital Temp-Humidity Sensor.
• LDR [Analog]:
  • Low Cost, Simple & Easy to use Light Sensor. Just add fixed resistor to from volt. Divider and you are ready to go.

W-Less Connectivity:

• ESP-01:
  • No doubt, It's the best, it's the cheapest, Couple of AT cmds, and you are connected to web.
• Xbee :
  • OK, Xbee still is widely used radio modules around. At my university there are many students & researchers who use them daily.

GPIOs:

• Analog: 1x6 Pin Header = 2 nos.
• Digital: 1x5 Pin Header = 4 nos.
• SPI Pins: 1x6 Pin Header = 2 nos.
• I2C Pins: 1x4 Pin Header = 4 nos.

You might have few questions in your mind:

• Why Xbee radio sockets?

Ok, As stated earlier. Xbee family is available & used almost every where and plus they have been around for while, we are using them for past 4 years, works great. Although they are costly compared to others like- HopeRF, Dorji RF modules.

If you go through the Xbee series, one good thing is that all of them are pin compatible, works serially on AT cmds. that means, you just have to plug-&-play according to your application.

Click the link below to discover more about them.

Xbee Radio Family

• Why GPIOs are like that?

Well, I know Arduino-like pinouts are best. but still they are little cumbersome to access while you are hooking some sensors & actuators.

So, I decided to go with this insane idea to put Analog & Digital pins on both side of the platform. Plus, I also added extra SPI & I2C pins, they might come handy.

I have also added +3.3V and GND pin on each connector, listed above.