Easyduino/Atmega328p Arduino Uno

Easyduino Arduino

The Microcontroller that propelled the Maker and Hobbyst movements

Schematic

Gerbers

Specs

• Input Voltage: 6.5V-15V(External Source Vin) 5V (USB). Both can be used at the same time.
• 5V Output Current: 1A (External Source) 500mA (USB)
• 3.3V Output Current: 500mA (External Source) 250 mA (USB)
• Polarity Protection (External Source) diode D2
• Overcurrent Protection: None (External Source) 1A (USB)
• 5V Autoselector: can take both USB and external source. A diode will avoid short circuit
• External Input Polarity protection: A diode will protect the circuit from a wrongly inserted battery.

References

Atmega 328p

Reset

• Atmega Hardware Design Considerations p7,p8 -> 10kR, 100nF cap and 330R for switch. The 100nF is not used in Arduino (produces erors with DTR)
• The 100nF capacitor on DTR (CH340C) is used for tricking Arduino into Bootloader mode, it produces a voltage spike.

Crystal

• Atmega Hardware Design Considerations p16 -> 22pf

AVCC

• Atmega328 Reference Manual p213 -> 10uH ferrite bead and 100nF
• The Analog tracks aren't critical. I won't create an analog ground for these tracks

ICSP Connector

• Atmega Hardware Design Considerations p12

AREF

• Atmega Hardware Design Considerations p6 -> 100nF

USB-C

Filtering

• USB Hardware Design Guidelines for FTDI ICs p8 -> 10nF Cap + Ferrite Bead + 100nF Cap + 4.7uF Cap
• I disregarded such heavy filtering for the easier to implement 1uF and 100nF cap given in the CP2102 datasheet
• I added a polyfuse with Ihold=500mA and Itrip=1A.

Differential Pair

• USB needs 90 Ohm differential traces.
• According to JLCPCB impedance calculator, with a JLC7628 prepreg and 6mil (0.15mm) space between lines
• I have to use 9 mil tracks -> 0.2 mm
• I will use a very short trace for D+ D- (around 2mm)
• I have to place vias because of the pinout of USB C and CP2102. Some other people have done it with no problems

CH340C

• Ch340 Datasheet: p10 -> 100nF between GND and V3.
• Ch340 Datasheet: p10 -> 100nF between GND and Vcc. Vcc to Vusb

AMS1117

• AMS1117 p4 -> 22uF tantalum capacitor on output
• I will use a 22uF to reuse the same capacitor
• I will reuse the output capacitor of AMS1117-5V to be the output capacitor of AMS1117-3.3V

5V autoselector

• If USB is present and no external input voltage. The USB will power the ATMEGA
• If USB is present and there is external input voltage. The external voltage will power the ATMEGA
• If USB is not present and there is external input voltage. The external voltage will power the ATMEGA

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