Arduino UNO Clone for DIYers - 2nd Episode

5 May 2020

Some of you may have already seen my posting about the Arduino UNO Clone for DIYers. The Arduino compatible board introduced on that posting was actually built for helping my daughter with her Arduino projects and was very successful. I and she have built several of them and used them well for studying Arduino and for some projects.

My daughter has recently made a music box with one of them. It is finished in a small box with 3 buttons. If one of the buttons is pressed, it plays the melody assigned to the button among 3 different melodies stored in the box.

I think she has done a good job but she still wants to make it enhanced and able to play longer melodies while keeping the existing hardware and the case.

I decided to build another Arduino compatible board with more memory to store longer melodies and this is it!

[ PIC 1 ] R1 in action

Please understand that the completeness of this may not meet your expectation as it is designed solely for my personal use.

1. Objective

a. It should be compatible with Arduino UNO.

- Arduino IDE should work with it.
- It should not additionally require any programmer, adaptor, Serial to TTL(UART) converter or etc. to program.

b. Shields for Arduino UNO should work with it as well.

- The board size and the shape should exactly be the same with the original Arduino UNO so it can directly replace the Arduino UNO board in my daughter's music box.
- All components except for the Barrel Jack for external power source, shouldn’t be taller than headers to be able to use various shields designed for genuine Arduino UNO.

c. It should be easy to build and easy to use.

- Bigger through-hole components should mostly be used for the people doesn’t enjoy soldering SMD.
- USB C type cable should be used instead of Standard B type.

d. Its circuit should be simplified for a better understanding.

- Use the parts easy to find or I currently have.
- Eliminate or simplify power selection circuit, crystal, 2nd microcontroller for Serial to TTL converting, headers for reprogramming the 2nd microcontroller and etc.

e. It should have enough memory to store more data.

- We should not forget that its major objective is to store longer melodies in the music box.

2. Circuit Design

a. Microcontroller:

- I looked up datasheets of many microcontrollers and compared them with ATmega328 of Arduino UNO for long time to find the most compatible DIP type microcontroller with ATmega328 but with more memory.

- My decision this time is to use ATmega1284 even if it is quite big to be placed on the Arduino UNO board.

- Arduino bootloader for ATmega1284 can easily be found from the internet. I used MCUdude's MightyCore with its Bobuino pinout and my ATmega/ATtiny Microcontroller Programming Shield for Arduino As ISP R2 to burn the bootloader.

- ATmega1284's register bit structure is exactly the same with ATmega328's. It lets most of all Arduino UNO compatible libraries and sketches work on the board with ATmega1284.

- Please find the comparison between ATmega328 on Arduino UNO and ATmega1284 on the Arduino compatible board to be built.

b. Power Source Selection:

- I just used Schottky diodes for it just like the Arduino UNO Clone on my previous posting. Please find the details from it.

- Unlike my previous design, Vin is directly shorted to the external power source from the barrel jack without a diode because Vin should sometimes be used for checking the voltage supplied by a external power source.

c. Power Regulators:

- I used SOT223 SMD type 1117V5 and 1117V33 for 5V and 3.3V voltage regulators respectively instead of TO220 through-hole type devices used for my previous design to save space on the board as ATmega1284 is too big to let the 2 big through-hole type regulators placed on the board with it. It is fine as my daughter is now able to solder relatively bigger SOT223 SMDs.

- Please find the details from my previous posting.

d. Serial to TTL(UART):

- I used CH330N just like the R1 model on my previous posting.

e. Buffer to drive the built-in LED for the digital pin 13:

- A small NPN type transistor, FJN3305R, which bias resisters are included in the package is used for it to save the space on the board.

- Please find the details from my previous posting.

f. USB Jack:

- I decided to use a USB C type jack to be in line with the trend.

- There are a few through-hole type USB C jacks in the market. I just used a SMD type device for R1 model as I currently have some in stock and a through-hole type device for R2 model.

- FYI, I actually built 3 slightly different models, R0~R2. The only difference among them is the type of USB jack. 5 pin Micro B SMD type, USB C SMD type and USB C through-hole type jacks are used for R0, R1 and R2 respectively.

3. Schematic

[ PIC 2 ] R2 Schematic

4. Parts

Annotation	Product	Type/Value	Quantity	Part Number	Remark
U1	IC	CH330N	1	CH330N	Jiangsu Qin Heng CH330N - USB to Serial Converter
U2	IC	REG1117-5REG1117-5	1	REG1117-5	TEXAS INSTRUMENTS - IC, V REG LDO 0.8A 5.0V, SMD, 1117, SOT-223-3
U3	IC	REG1117-3.3	1	REG1117-3.3	TEXAS INSTRUMENTS - IC, V REG LDO 0.8A 3.3V, SMD, 1117, SOT-223-3
U4	IC	ATMEGA1284P-PUATMEGA1284P-PU	1	ATMEGA1284P-PU	MICROCHIP - 8 Bit MCU, Low Power High Performance, AVR ATmega Family ATmega128 Series Microcontrollers, 20 MHz
U4	IC Socket	20P SIP x 2	2	310-47-120-41-001000	MILL MAX - SIP SOCKET, 20POS, 2.54MM, THROUGH HOLE
Q1	Transistor	FJN3305RTA	1	FJN3305RTA	ON Semiconductor - Pre-Biased Bipolar Transistor (BJT) NPN - Pre-Biased 50V 100mA 250MHz 300mW Through Hole TO-92-3
A1	Header	6P, 2.54 mm	1	2212S-06SG-85	MULTICOMP - Board-To-Board Connector, 2.54 mm, 6 Contacts, Receptacle, 2212S Series, Through Hole, 1 Row
	Header	8P, 2.54 mm	2	2212S-08SG-85	MULTICOMP - Board-To-Board Connector, 2.54 mm, 8 Contacts, Receptacle, 2212S Series, Through Hole, 1 Row
	Header	10P, 2.54 mm	1	2212S-10SG-85	MULTICOMP - Board-To-Board Connector, 2.54 mm, 10 Contacts, Receptacle, 2212S Series, Through Hole, 1 Row
J1	Jack	Barrel Jack	1	FC68148	CLIFF ELECTRONIC COMPONENTS - DC Power Connector, Jack, 5 A, 2.1 mm, Through Hole Mount, Through Hole
J2	Jack	USB C	1	USB4085-GF-A	GCT - USB Connector, Charging Connector, USB Type C, USB 2.0, Receptacle, 16 Positions
J3	Header	6P(ICSP), 2.54 mm	1	2213S-06G	MULTICOMP - Board-To-Board Connector, 2.54 mm, 6 Contacts, Header, 2213S Series, Through Hole, 2 Rows
J4	Header	2x6P, 2.54 mm	1	2214S-12SG-85	MULTICOMP PRO - PCB Receptacle, Board-to-Board, 2.54 mm, 2 Rows, 12 Contacts, Through Hole Straight, 2214S Series
R1, R2	Resistor	1K Ohm, 125mW	2	MCCFR0W8J0102A20	MULTICOMP - Through Hole Resistor, 1 kohm, MCCFR0W8J Series, 125 mW, ± 5%, Axial Leaded, 200 V
R3	Resistor	10K Ohm	1	MCCFR0W8J0103A20	MULTICOMP - Through Hole Resistor, 10 kohm, MCCFR0W8J Series, 125 mW, ± 5%, Axial Leaded, 200 V
R4	Resistor	1M Ohm	1	MCCFR0W8J0105A20	MULTICOMP - Through Hole Resistor, 1 Mohm, MCCFR0W8J Series, 125 mW, ± 5%, Axial Leaded, 200 V
RN1	Resistor Array	4x1K Ohm	1	4605X-101-102LF	BOURNS - Fixed Network Resistor, 1 kohm, 4600X Series, 4 Elements, Bussed, SIP, 5 Pins
C1 ~ C7	Capacitor	0.1uF	7	MCFYU6104Z6	MULTICOMP - Ceramic Disc Capacitor, 0.1 µF, 50 V, MCFY Series, +80%, -20%, Y5V, 5 mm
C8, C9	Capacitor	47uF 25V	2	UHE1E470MDD1TD	NICHICON - Electrolytic Capacitor, Miniature, 47 µF, 25 V, HE Series, ± 20%, Radial Leaded, 5 mm
C10	Capacitor	10uF 6.3V	1	EEA-GA1C100H	PANASONIC - Electrolytic Capacitor, 10 µF, 16 V, GA Series, ± 20%, Radial Leaded, 4 mm
SW1	Switch	2P or 4P tect	1	MJTP1230A	APEM - Tactile Switch, MJTP Series, Top Actuated, Through Hole, Round Button, 160 gf, 50mA at 12VDC
D1, D2	Schottky Diode	1N5819	2	1N5819RLG	ON SEMICONDUCTOR - Schottky Rectifier, 40 V, 1 A, Single, DO-41, 2 Pins, 600 mV
D5	LED	L, Yellow, 3mm	1	L-7104YC	KINGBRIGHT - Yellow LED 3mm Through Hole
D6	LED	RX, Red, 3mm	1	L-7104EC	KINGBRIGHT - Red LED 3mm Through Hole
D7	LED	TX, Blue, 3mm	1	L-7104VBC	KINGBRIGHT - Blue LED 3mm Through Hole
D8	LED	ON, Green, 3mm	1	L-7104GC	KINGBRIGHT - Green LED 3mm Through Hole
Y1	Resonator	16MHz, 20~30pF	1	AWCR-16.00MD	ABRACON - Resonator, Ceramic, 16 MHz, Through Hole, 3 Pin, 40 ohm, ± 0.5%, 30pF, AWCR Series
PCB1	PCB	Custom(1284R2)	1	NA

5. PCB

The gerbers files are attached.

[ PIC 3 ] R2 PCB Layout

5. Assembly

I had to do some trick to fit all the components in the small space on the PCB and to make it look better. I put most of all ceramic capacitors, resisters and a resonator in the thin space between the microcontroller and the PCB.

You can make it better than this with smaller axial type capacitors. I used the bigger disk type capacitors as I have too many of them in stock and wanted to use them off first.