Arduino is fun. It's a great open source hardware platform for students and hobbyists for realizing their ideas. Sometimes you will have to put your working project somewhere fixed. An Arduino UNO board costs around INR 1,400 (USD 22). So it's not a good idea to use a whole arduino board for a single project. Also the Arduino is an ATmega328 development board and it is not meant to be directly implemented in a project or product as it is given. It's just for prototyping your ideas. So what if you want to use the microcontroller in a standalone project ? You can design your whole circuit to generate a PCB, print and use it. But my opinion is to design a standalone ATmega328 board with the minimal components that can be directly plugged into your application specific circuit board instead of soldering all the components. It is a kind of modular approach and I'm a fan of it. What do you think ?
The following is ATmega328P-PU pin configuration with corresponding Arduino pins. The pinout is compatible with Atmega168 and ATmega8 too.
Following is an ATmega328 schematic with minimal components and a programming ICSP header. You can replace the MCU with ATmega168 and ATmega8 if you want. The coupling capacitors must be as close to the pins as possible and their leads must be short as well.
Instead of printing a PCB like I said above, I soldered two of them in a perforated board (Hoosh!). I really like soldering, you know. Practice makes it perfect.
The debug jumper will enable us to connect a green LED to the digital pin 13 whenever we want instead of permanently connecting it to the pin 13 like seen in the official Arduino board.
Here are some images of the boards I built and good luck with your next Arduino project.
If you're in a hurry, it's better buy one of those cheap Arduino compatible Nano boards from eBay or Amazon instead of making this.