UPDATE: Thanks to Rando, now you can order this PCB on OSH Park. Thanks!!

UPDATE: If you’re interested in mount the board yourself, now you can download the Bill Of Materials (BOM). Happy welding!

Hi all! With a bit of delay, here’s my last work, a PICnano breadboard based on the PIC18F2550 microcontroller. I have in mind a new project and I want to use an small board, like the Arduino Nano board. This new project is battery powered (3,7V Li-Ion battery). After checking the schematics of the Arduino Nano, I see that the microcontroler is powered at 5V. Of course, I can unmount the linear regulator (U3) that is on the board, and bypass the VIN to the microcontroller power supply. But I think it’s funny try to develop a new module when you’ve access to the microcontroller power supply! Also, I want to work with PIC microcontrollers after many years, so here’s what I design!

• The Hardware

The goal of this new design is try to have an Arduino Nano compatible module but with some new features, such have direct access to the power supply microcontroller. First of all, here you can download the schematic of the board: PICNANO BREADBOARD SCHEMATIC V1.0

The board is based on the PIC18F2550 microcontroller, here you can download the datasheet. It’s an 8-bit microcontroller with these features (from the Microchip’s page):

Program Memory Type	Flash
Program Memory (KB)	32
CPU Speed (MIPS)	12
RAM Bytes	2,048
Data EEPROM (bytes)	256
Digital Communication Peripherals	1-UART, 1-A/E/USART, 1-SPI, 1-I2C1-MSSP(SPI/I2C)
Capture/Compare/PWM Peripherals	2 CCP
Timers	1 x 8-bit, 3 x 16-bit
ADC	10 ch, 10-bit
Comparators	2
USB (ch, speed, compliance)	1, FS Device, USB 2.0
Temperature Range (C)	-40 to 85
Operating Voltage Range (V)	2 to 5.5
Pin Count	28

 

These characteristics are enough for many of the small projects I usually do. The two features that are more important for me at this time are:

– It has a full speed 2.0 USB internal module, so you don’t need external transceivers to have a USB interface.

– Power supply starts at 2V, so it’s perfect for a battery powered systems.

The schematic is dividen in functinal blocks:

PIC18F2550 Microcontroller

The main part of the board. It has the basic elements to work with the PIC without external componentes: decoupling capacitors, reset pushbutton, mini-USB connector and external oscillator. And, obviously, the PIC18F2550 microcontroller in 28-pin SOIC package.

Header Connectors

The board has two 15-pin connectors, J1 and J2. The space between pins in each connector is a standard 0.100 inches. The distance between both connectors are 0.600 inches. This allows to use the board in a bread board for fast prototyping. Most of the signals are compatible with the Arduino Nano pinout. Main differences are on pins 13, 14 and 15 of J2. In the PICnano board, in these pins are the VUSB and VCC_EXT power supplies.

Power Supply Selection

The microcontroller of the board can be powered (VCC_UC) from any of these power supply sources:

– From VCC_EXT pin (J2, pin 14). In this case, the microcontroller power supply is the same that you apply on this pin. The limits are the same of the microcontroller operating voltage (2V to 5.5V), and you can use it to power the board from a Li-ion battery dicrectly. BE CAREFULLY when you use this power supply, you acts directly on the microcontroller VDD pins!!

– From an external USB port (VCC_USB).

– From an external VIN power supply (J2, pin 1). The board is ready to mount a linear LDO regulator (NCP1117), like the Arduino Nano board. In this case, the maximum imput voltage is 20V. The NCP1117 has many different output voltages, so you can select the right one according your application (1.5 V, 1.8 V, 2.0 V, 2.5 V, 2.85 V, 3.3 V, 5.0 V).

To select the power supply font, you have a jumper on the board (SW2), the yellow one in the image:

With the jumper in the left position (seeing from the USB connector), the power supply can be from USB or external VIN. On the right position, the power supply is VCC_EXT, directly to the microcontroller power pin.

ICSP Connector

The standard connector from Microchip to program their devices. I use the Pickit3 tool, that also allows debbug the code with the MPLAB environment. This connector is the one you can see behind the jumper.

User Led

A general purpose red led on the UART TxD pin. It’s usefull to start working with the board or for developing the application.

• PCB Design

The board was designed with Altium Designer 13, and you can download the gerber files here: GBR_PICNANO_BREADBOARD_V10. It’s a 4-layer PCB, and the dimensions are 46,5 mm x 18mm. It’s only 3mm longer that the Arduino Nano one. To manufacture the board, I use the DirtyPCB services. I like their board quality on 2-layer boards (see my last project) and I want to test the 4-layer designs. And the result is excelent again:

[metaslider id=1125]

And here’re some photos with the board mounted:

[metaslider id=1137]

•  The software

To test the board and validate both the design and the mounting, I make a small program to flash the red led (the classic ‘Hello World’ with leds!!). I use the Mikro C PRO compiler, from MikroElektronika. I like this compiler because offers a lot of libraries with samples and code ready to use. Also, they’ve got a bootloader for this microcontroller (you can download here). So, you can burn the PIC once with the bootload code (using a programming tool) and after you can upload your code to the PIC with a PC tool, eliminating the need of an external programmer!

The code is as simple as you can imagine:

If you’re interested, here you can download the full project, including the source file, *.hex and config settings: PICNANO_HELLO_WORLD.

Finally, on the Embedded-Lab blog you can find a great article of how to getting started with the PIC18F2550 microcontroller.

• 
• 
• 
• 
• 
• 
• 
• 

This post is also available in: Spanish