Standalone Arduino Uno

I made a standalone Arduino Uno with the same board dimensions as well as mounting holes as the original. As I get more into using Arduino's for projects, I will have boards I can use in those projects instead of buying a ready made boards.

With the standalone, I can mount the female headers on the top like a standard Arduino, or I can mount male headers on the bottom of the board so I can plug the board into a project. I have changed the NC (Not Connected) pin to connect to DTR when using a USB to serial module to upload, and added the capacitor for this as well.

This board has an LED for power, LED for Blink test, reset button, and +5 and +3.3 volt regulators powered by a 9-12 volt barrel plug. The only parts surface mounted are the voltage regulators. If you do not use 3.3 volts in a project, you can omit 3 parts from the assembly.

Knowledge of soldering and reading schematics is helpful.

Functions of each component will be stated in each build step.

Parts:

Standalone Arduino PCB, gerber zip and schematic are 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, x3

LED, 3mm, green, x2

barrel jack, x1

tactile switch, x1 (2 pin)

header pins, single row, female for top mount, male for bottom mount (a 40 pin row and that will be described to get that ready)

standoffs and screws, x4 (M3 screw, standoff length of your choosing, I used 6mm)

Power supply rated 9 to 12 volts and 2 amps is more than sufficient. I use a 9 volt 2 amp supply with a on/off switch on the cable, which is very convenient.

Tools:

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

Soldering iron and solder.

Braid and liquid flux, if mistakes are made.

Tape, for holding components in place.

Needle nose pliers, used for pulling pins on the header.

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, used when soldering in the pin headers.

How you want to mount the header pins will determine steps to installing the parts.

Female Headers on Top: install parts lower than the header, then when installing the headers, the board can be turned upside down when installing the female headers.

Male Headers on the Bottom: install the male headers first by turning the board upside down and using breadboards or pin header tool to hold them in place. Once the headers are out of the way, just start installing parts with lowest profile to tallest profile.

Determine if you want 3.3 volts available on the header pin: If you do not use 3.3 volts in a project you are building this standalone board for, you can omit three parts: U3.3V, C10, and C11. If you do want 3.3 volts on the header pin, just proceed with the steps.

My first build was with female headers so I started with lowest profile parts first. First added the voltage regulator, then resistors, then the crystal. I installed only the 5 volt regulator as the 3.3 volt regulator has not arrived yet, and it is not a show stopper, can easily be added at a later time, or even omitted if you are not going to use 3.3 volts.

For the voltage regulators, even if you have not soldered surface mount components before, this is fairly easy and straightforward. The regulators are actually big for surface mount components, some parts can be very tiny.

For the regulators, first, add some solder to one of the three small pads, place the component on the pads and hold in place with tweezer tip, place the iron on the lead with the solder on the pad, and when it flows the IC will settle onto the pad and the lead will be soldered in place. Now just solder each IC lead and you can see it when it flows onto the pad and lead. Solder the tab the same way, and there is a copper pour under the tab which acts as a heat sink. Repeat with the second regulator.

For the thru-hole components, simply form leads on the resistors, fit in place, tape to secure, solder, trim leads. For the crystal, just insert into the holes, tape, solder, remove tape, and trim leads.

Functions:

U5V, U3.3V, these are the voltage regulators, the barrel jack provides 9-12 volts and the regulators reduce that to a clean 5 and 3.3 volts.

R1, R3, these are current limiting resistors for the "On" and "Blink" LEDs.

R2, this is a pull up resistor on U1 pin 1, the Reset Pin. This connects to 5 volts and ensures the reset pin does not float or reset inadvertently.

X1, is the 16 MHz crystal and provides a stable clock for the microcontroller for its functions.

For this step I added the disc capacitors and the reset switch.

For the capacitors, ensure C5 and C6 are the 22pF ones to ensure correct timing on the crystal.

Insert components, tape in place, solder, remove tape, and trim leads. Repeat the steps for remaining disc capacitors and the switch.

Functions:

C2, C3, are part of the filtering for the 5 volt regulator.

C5, C6, are load capacitors and ensure the crystal is operating within its specified range.

C7, C8, are decoupling capacitors to filter out noise and stabilize the supply voltage.

C9, used only when connecting DTR (mistakenly labeled as DTS by me) and is used to create a short low pulse when programming the microcontroller.

C11, is part of the filter for the 3.3 volt regulator. Can be omitted if you do not require 3.3 volts on the board.

C12, decoupling capacitor for the external analog reference voltage.

SW1, is the Reset switch, pressing this sends a ground to U1 pin 1 to reset the microcontroller.

This step will involve DIP-28 socket, LEDs, and the female headers.

For the socket, align the notch on the socket to the notch on the silkscreen, tape in place. Solder one lead in opposite corners, remove tape then check to ensure the socket is lying flat on the board, reflow the corners to adjust as needed, then solder the leads in the other corners, then solder remaining leads.

For the LEDs, make sure you have the flat side of the LED aligned to the flat side on the silkscreen. Tape in place, solder, remove tape, and trim leads.

For the female headers. There is two rows, the row for the digital pins is two sections and the spacing between each section is not 2.54mm (0.1") standard, so you will need to either use a 40 pin row and fabricate your own or purchase ready made headers to length. For the digital pins row, you need a 10 pin row and an 8 pin row. I fabricated the ones I used, it is easy.

To fabricate these rows from a 40 pin header, simply count out 10 pins or rather leads, use needle nose pliers and pull the 11th lead (pin) out. At the hole where pin 11 was, score the side of the header with a fine tooth saw, on both sides, then you can snap the 10 row piece off. Use flush cutters to trim excess from the cut ends of the headers and rub on a piece of fine grit sandpaper to smooth it out. Repeat with the 8 pin row.

For the other section of header, there is two parts, there is an 8 pin row and a 6 pin row. The spacing between these is standard, so instead of cutting a header into two section, just cut it to 15 pins long, count to 6 from one end and pull out the 7th pin, now you can use that header in one length instead of two pieces.

To solder in the headers, use a breadboard or pin header tool to hold them in place, using male headers to fit into the breadboard/tool. Place a weight on the board to hold in place, solder a pin at each end, then check that the header is square to the board, then solder the remaining pins.

Functions:

D1, is the On indicator, lit when power (9-12 volts) is applied through the barrel jack J1, or in VIN pin.

D2, is the Blink indicator, which is tied to pin 13 on the digital pins like the original. This is so when you load a Blink sketch to verify you can program the microcontroller, the LED will blink as stated in the sketch. D2 also rapidly flashes when the Reset switch is pressed.

U1, the socket holds the ATMEGA328PU microcontroller.

Headers, the pin layout is exactly the same as an Arduino Uno, except the NC pin has been changed for use as DTR when using a USB to Serial module to load sketches.

Last items to install are the barrel jack and the electrolytic capacitors.

The barrel jack is straightforward, it only fits the board in one way, tape that in place, lightly solder two pins, check to ensure the jack is sitting firmly on the board, then solder the pins well.

For the electrolytic capacitors, ensure you have the negative lead to the white mark on the silkscreen.

Functions:

C1, C4, C10, are part of the filtering for a smooth clean 5 and 3.3 volts.

J1, is the input power to the board. The voltage for this is from 9-12 volts. An alternate voltage input, also 9012 volts, is the VIN pin. Either way can be used for supply voltage, NOT both at the same time.

I did burn the bootloader onto the microcontroller, and loaded the Blink sketch after and it worked perfectly. I am very happy with how this project turned out.

Would you like me to state the steps to burn the bootloader and or upload a sketch?

I am going to update this board to Ver 1.1 with another header for use with FT232RL USB to Serial module used to load sketches on the standalone. So instead of connecting the 5 wires, you will just insert the module pins into the header.