The Nano V3.0
An ATmega328P that runs at 16 MHz, a CH340C that turns USB into serial, and two regulators behind three ways of being powered. Four lights tell you what it is doing: ON, TX, RX and D13.
What is on it
The board is 43.2 x 18 mm. The chip is an ATmega328P in a 32-pin flat package, with a 16 MHz resonator beside it: 32 KB of flash for the program, 2 KB of RAM, and 1 KB of EEPROM that keeps its contents with the power off. Fourteen digital pins (D0 to D13), six of them with PWM (D3, D5, D6, D9, D10, D11), and eight analogue inputs. A6 and A7 are analogue-in only: they cannot be set to output, and have no digital use at all.
A CH340C does the USB. It turns the USB-C socket into the chip's serial port, which is how a sketch is uploaded and how the Serial Monitor works. The USB-C socket has two 5.1 kohm resistors on its CC lines, which is what lets a USB-C supply offer its 5 V.
There is a reset button, and a 2 x 3 ICSP header at the other end from the USB-C socket (MISO, 5 V, SCK, MOSI, RESET, GND) for programming the chip without the bootloader.
The pins
Two rows of 15, 2.54 mm apart along the row, 15.24 mm between the rows. Row A runs VIN, GND, RST, 5V, A7, A6, A5 to A0, AREF, 3V3, D13, and ends at the USB-C end. Row B runs TX, RX, RST, GND, D2 to D12.
Under the board are male pins, 8.4 mm long, which is how it plugs into the shield's sockets. The top face carries the same holes with the names printed beside them, so a jumper wire can go in from above.
The four lights
ON is lit while the 5 V rail is up. TX and RX are driven by the CH340C and blink when the chip and the computer talk. D13 is on pin D13, so it is the light that a Blink sketch uses, and it is also the SPI clock pin, so it flickers when SPI runs.
Three ways of being powered
The 5 V rail is the heart of it, and two things can feed it.
USB reaches the rail through a Schottky diode. The diode costs a little voltage, and the schematic carries a note that the first diode chosen dropped too much. VIN goes through an AMS1117-5.0, a linear regulator, so VIN has to be above 5 V: the classic Nano takes about 7 to 12 V. The difference is shed as heat in the regulator.
The 3V3 pin is a third, smaller output. A separate regulator, an ME6217C33M5G, makes 3.3 V from the 5 V rail, so 3V3 only exists once USB or VIN has brought the rail up. It is for light loads; this book does not give it a number, because the datasheet's headroom is not the board's budget.
The two parts on the back
The CH340C, the AMS1117-5.0, the diode and the 3.3 V regulator are on the underside, so the top face is the chip, the button, the header, the lights and the USB-C socket.
When it does not work
Whether this board ships with the old or the new bootloader is not something this book has verified. If the upload fails with not in sync, choose Processor: ATmega328P (Old Bootloader) in the Tools menu and try again. If that is already your choice, try plain ATmega328P.
Use a cable that carries data; some are charge-only. Then check that the computer has a driver for the CH340C. Recent Windows and macOS versions usually carry one; if yours does not, install the CH340 driver from its maker.
The 3V3 pin is a small output from a regulator that is fed from the 5 V rail. It is for a light load such as a sensor. Power anything larger from its own supply and share the ground.
ON follows the 5 V rail. With a USB cable, try another cable and another port. If you are powering it on VIN, check the voltage is above 5 V; the regulator can only lower a voltage.
What the shield adds under the Nano: a light on 22 of the 28 pins, and three places each pin comes out.
The PinPulse shield →Edit this page — content/books/nano/the-nano.mdx
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