- This page goes over various methods, as well as OSE's efforts to make an Arduino using only the core componets and either a prototyping board or a custom pcb
OSE Working Doc
- USB to serial converter - 
- What is DTR - Data Terminal Ready - or reset button - ]
- Connecting USB to Serial converter - 
- More instructionals on how to wire Serial to USB -  and .
- Does CP2102 work? Probably.
- FTDI works - see another tutorial with FTDI converter - 
Parurino by Nadya Peek
Has a serial port, not USB, so is a bit antiquated. http://infosyncratic.nl/projects/parurino/
You can use an existing Arduino to burn a bootloader and to program the arduino:
YES: USB is the way to go for modern devices as of 2019
Build your own arduino for about $5 in parts - Julian Ilett -
- USB to serial - 
DIY Arduino Mega
- Requires surface mount, but is empowering when done correctly. This one didn't work because you can't program it? - https://www.instructables.com/id/DIY-Arduino-Mega-2560/
- Another - can do it - essentially breakout of the microprocessor chip. Is it programmed with the simple plug? 
Arduino can be used a very popular open hardware component and can be successfully used in lots of open source projects:
Although you can always make your own arduino using a breadboard using the following instructions: http://itp.nyu.edu/physcomp/Tutorials/ArduinoBreadboard
A similar project could be making you own arduino using a perfboard. http://hackduino.org/mapblog/?page_id=46
Another take would be to create YOUR OWN Arduino PCB using following instructions on this project http://www.theparsley.com/arduino/diy/
In terms of cost most DIY guides featured here will cost you more money (in you add up the labor cost) than a prefabricated arduino board. But for larger quantities the guides could be cost effective. Although using a perfboard or ever a breadboard for could be useful for prototyping using a PCB (DIY of prefabricated) could be more a more practical solution for finished products.
Different Routes to DIY Arduino
- Deadbug without socket with components soldered directly to pins makes for a Minimalist Arduino.
- Deadbug minimalist - Minimalist_Arduino#Further_Simplification - by omitting most of the components,to the limit of just chip with crystal oscillator mechanism
- Breadboard Arduino Uno kit of parts for $10 from Jameco, Atmaga 328P has bootloader. This also has an instructional for how to build it. Bravo to Jameco. . Programmable via FTDI Breakout Board or by in-system programming using another Arduino Uno.
- Good Instructable on making an Arduino uno. Note that you can get rid of any programming interface simply by taking the microprocessor chip off the DIY arduino and inserting it onto an off-the-shelf arduino - and programming the chip on the off-the-shelf arduino! Here is How to Remove a Chip from Arduino
- Instructable on building an Arduino from a professionally-made PCB then soldering. Includes USB and USBASP. 
- Not as practical, but this one seems to be made with no pcb but instead wire from a Wire Bending Machine . This is similar to Deadbug Soldering but with the wire bends creating what appears to be an orderly structure. Just watch your short circuits on this one!