Introduction: Standalone Arduino UNO Ver. 2

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About: Retired Navy Chief, with background in electronics repair and maintenance including multilayer boards using a microscope. Navy Instructor for my last 6 years. Now a hobbyist with electronics, woodworking, and …

This version adds a 6 pin female header to connect a USB to serial module to facilitate loading sketches into the Arduino.

I built two versions of this, one with female headers for all the pins, and one with male headers so it can be plugged into another project, which is most of the build photos. One is built with the 3.3 volt components, and one is not.

The reason for building this is two fold, it helped me learn a lot of how the circuit is working, and for use in other projects - even though clones are quite inexpensive, I can tailor boards to what I need; such as omitting the 3.3 volts if my project does not require that, putting male pins on the bottom of the board for plugging into a project, and the ease of using the female header for the USB to Serial module when loading a sketch.

For this project, you need basic soldering skills and be able to read schematics. There is two surface mount components on the board, which can be easily installed with just a regular soldering iron - no special equipment is needed.

Component functions will be explained in each step during assembly.

Attachments

Supplies

Parts:

PCB can be ordered here, and the gerbers and schematic can be downloaded from my proton drive here.

ATMEGA328P, x1

AMS1117-5.0, x1 (5 volt regulator, SOT-223 surface mounted)

AMS1117-3.3, x1 (3.3 volt regulator, SOT-223 surface mounted)

16 MHz crystal, x1

10K resistor, x1 (1/4 watt, 1 or 5% is fine)

4.7K resistor, x2 (1/4 watt, 1 or 5% is fine)

22pF disc capacitor, x2

100nF disc capacitor, x7

10uF 25v electrolytic capacitor, x2

10uF 25v tantalum capacitor, x2

LED, 3mm, green, x2

barrel jack 2.5x2.1mm center positive, x1

tactile switch, x1 (2 pin)

header pins, 2.54 pitch, male or female, and that will be explained.

Tools:

Schematic, I use reference labels for components, so you have to view the schematic for component values.

Soldering iron and solder.

Braid and liquid flux, if mistakes are made.

Tape, for holding components in place.

Small standard screwdriver or tweezers, for holding the surface mount components.

Needle nose pliers, used for pulling pins on the header, and straightening pins on the socket and IC.

Fine tooth saw, for scoring the header.

Fine grit sandpaper, for smoothing the ends of headers.

Flush cutters, for trimming leads.

Isopropyl alcohol and brush, for cleaning the board when completed.

Breadboard or Pin Header Tool or an Arduino UNO with female headers, used when soldering in the pin headers.

Multimeter with hook probes, for testing.

Step 1: Lowest Profile Components First

First, determine what the board is going to be used for, this will help you determine if you need to install the 3 components for 3.3 volts, and what header pins you want to use. If you plan on using the board as a plugin to another board, you may want male headers on the bottom, or even the extra long male headers. If you want the board as a regular clone, you may just want the female headers.

Either way, the first thing we are going to install is the voltage regulators, which are the surface mount components. These are small, but easily soldered in place with regular tools.

For most of the build photo, I used only a 5 volt regulator as 3.3 volts was not needed for the project this board is destined.

Heat one of the 3 small pads for the regulator (U5V) and apply a small bit of solder.

Now position the component on the pads and hold in place with a small standard tip screwdriver or tweezers.

Place the hot iron on the foot of the component and when the solder flows, you will see and feel it, the IC will sit flat on the board.

Now solder the other two feet, then solder the pad. See, that was very easy. If using the 3.3 volt regulator, just repeat the steps to solder that in place.

Next components to install are the resistors. Form the leads, place in the correct holes, hold in place with a piece of tape, solder, remove tape, check for solder on both sides of the board, trim leads, and repeat.

Next components are the LEDs, pay attention to the polarity when inserting those.

Install the reset switch, making sure the base is flush with the board.

Then install the crystal, insert into the holes, tape and place, solder, and trim.

Straighten the pins on the 28 pin socket, if needed, insert into the board, tape, and solder just 1 pin in each row, in opposite corners. Check to make sure the socket is seated flush on the board, solder the two other opposite pins, then solder all remaining pins.

Functions:

U5V, is the 5 volt regulator, which provides power to U1, the microcontroller and to the 5V pin on a header row. Rated for 800mA.

U3.3V, is the 3.3 volt regulator, rated for 800mA and only provides power to the 3V3 pin on a header row. If you do not need 3.3 volts on the board, you can omit adding this part.

R1, R3, are current limiting resistors for LEDs D1 and D2.

R2, is a pull up resistor for U1 pin 1, the reset pin. To prevent inadvertent resets to the microcontroller, R2 keeps pin 1 at 5 volts until the reset button is pressed.

D1, is the ON indicator, this lights when power is applied from the barrel jack or from the the USB to Serial module inserted in P1.

D2, is the BLINK indicator, this LED, just like the original UNO, is tired to digital pin 13 (which is U1 pin 19). This only lights when you are using digital pin 13 with a blink sketch or just using the pin to output a LL1.

X1, is the 16MHz crystal for clock functions in U1, the microcontroller.

U1, is the ATMEGA328P microcontroller fitted into a DIP-28 socket. The microcontroller is the brains to the UNO and executes sketches you have loaded into it.

SW1, this is the Reset button, pressing this button applies a ground to U1 pin 1, resetting the running sketch.

Step 2: More Parts

Now we can add the 22pF caps. This is straightforward, just insert, either direction is fine, tape in place, solder, trim leads.

Then go ahead and install then solder in the six 100nF caps, trim the leads.

Install and solder in the barrel jack, nothing to trim on this.

Install the electrolytic capacitors, paying attention to the negative lead and ensuring that it is inserted correctly. Solder and trim the leads.

If building the full UNO with 3.3 volts, go ahead and install C10 and C11, which are tantalum capacitors (per the data sheet for the 1117-3.3V regulator), ensure you have the + lead on the capacitor in the correct hole in the board.

Functions:

J1, this is a jack to accept a barrel plug of 5.5x2.1mm, the input voltage on this should be between 9 and 12 volts. I use a 9v 2a wall adapter with a on/off switch on cable.

C1, C4, these are electrolytic capacitors and are part of the filtering for the 5 volt regulator, filtering power before and after the regulator.

C2, C3, these are monolithic disc capacitors and make up some of filtering for the 5 volt regulator, filtering power before and after the regulator.

C5, C6, these are monolithic disc capacitors and in conjunction with the crystal X1 and the microcontroller, makes up the oscillator circuit.

C7, C8, C12, are monolithic disc capacitors and are used for decoupling.

C9, is used for the DTR (Data Terminal Ready) line to provide a pulse to let Serial and the microcontroller to be able to talk.

C10, C11, these are tantalum capacitors and filter the power before and after the regulator. If you do not need 3.3 volts on the board, you can omit adding these parts.

Step 3: Header Pins

For the previous photos, I am building this board as a plug in to another board, so for this I am going to add standard male headers for the two data pin rows, and I will use a female header for P1 to be able to accept a USB to Serial module.

For the male headers, you will need a breadboard or Pin Header Tool or an Arduino (recommended way) to get the pins straight.

When you look at the board and see the row with ANALOG and the power pins, this row is very easy as the spacing between the two sections (power and analog) is 2.54 pitch, so for this you simply need a single row male header of 15 pins, with pin 9 (when counted from the left) removed, and you have a row ready. Same principle applies to females headers, single row of 15 pins, with pin 9 (counted from the left) pulled.

Now for the DIGITAL pin row, there is a gap between the section, right between pins 7 and 8, which is less than 2.54 pitch, meaning you will need two pieces of male header. Measure and cut one piece of standard male header to 8 pins in length, and the other piece to 10 pins in length. Trim each end, and light sand. Same principle applies to female headers as well.

Using the recommended way, place the males headers gently into the female headers, not all the way, just enough so they are in place. Now you can fit your new board on top of the male header pins, check to make sure each row is sitting flush on the male headers. Solder a pin on each end of each section, make sure the board is flush to the headers, then solder remaining pins. For female headers, if you have a UNO board with male headers, you can use that for alignment, or you can just tape each section in place and carefully solder, ensuring the headers are flush with the board and vertical.

For the new header pin section, J1, you will need a female header with 6 pins, either cut one from a 40 p or a purchased one of 6 pins.

Place the female header into the holes for J1, tape in place, making sure the header sits flush on the board and is vertical. Solder a pin on each end, check for flush, solder remaining pins.

Clean the board with isopropyl alcohol, and your board is ready.

First two photos is the board I made with male headers, and the second board uses female headers as well as the 3.3 volt components as well.

Pins:

  1. NC
  2. IOREF
  3. RESET
  4. 3V3
  5. 5V
  6. GND
  7. GND
  8. VIN - only use when the barrel jack is not used, can be 9-12 volts on this pin to power the regulators.
  9. Analog In, 0
  10. 1
  11. 2
  12. 3
  13. 4 / SDA
  14. 5 / SCL

Pins:

  1. SCL
  2. SDA
  3. AREF
  4. GND
  5. 13
  6. 12
  7. 11
  8. 10
  9. 9
  10. 8
  11. 7
  12. 6
  13. 5
  14. 4
  15. 3
  16. 2
  17. 1 / TX
  18. 0 / RX

J1 pins:

  1. DTR - Data Terminal Ready, signal that tells Serial that U1 is ready for communications.
  2. RX - connected to Digital pin 1 / TX.
  3. TX - connected to Digital pin 0 / RX.
  4. VCC - connected to 5 volt rail.
  5. CTS - NC
  6. GND - connected to ground rail.

Step 4: Basic Testing

Power verification. Using two short wires or two single headers pins, insert a pin in ground, and one in 5V for the board with female headers. Set your meter to DC volts, and clip the ground line to the ground pin, and the positive line to 5V pin, if testing the board with male headers, just attach the probes to the pins on the underside of the board.

Turn on your board, and your meter should read right about 5 volts.

Now attach the positive line to the 3V3 pin, meter should read about 3.3 volts.

Load the Blink sketch. Remove the barrel plug. Plug in your USB to Serial module, connect module to your computer and upload the Blink sketch. Blink will verify the microcontroller is working.

Use your new board(s) as needed.