Picduino, Pic on the Arduino Form Factor

PROJECT OBJECTIVE: Replace the AVR processor on the Arduino form factor with a 28 pin 18F PIC processor. Add both an EEPROM and RTC to the design. Use thru hole, including DIP parts, to facilitate assemble.

FEATURES:

• 18F, 28 pin PIC processor (16F optional)
• Tiny bootloader with auto-bootloading (DS30 coming)
• Arduino pcb form factor
• Serial communication using breakout boards
• Stackable connectors with Arduino compatible pinout
• Dual LDO regulators for 3.3V and 5V.
• Power switch, 300ma
• Jumper for comm port power
• Onboard I2C RTC and EEPROM
• ICSP connector at front
• Reset switch accessible at front
• Testing LED on B0 at front

INTRODUCTION: Initially, the18F2520 will be used since there is an available Tiny bootloader that we have been using with good results. Presently, we are testing the 18F25K22 with the DS30 bootloader.

This design uses the Arduino physical stacking connectors, without change, except for some signal assignments. The USB circuit which is incorporated on the Arduino has not been incorporated on the Picduino, but will be contained on a breakout board allowing both RS232 and USB serial communication. The RS232 breakout will be available with the initial project and for USB communication the Sparkfun DEV 09716 will be used. This will provide the same USB functionality as the Arduino with the exception of powering the Picduino from the USB port.

The 18F2520, 18F25K22 and 18F25K20 use 5V and 3.3V respectively; therefore, dual LDO regulators have been provided. Dual regulators, also seem reasonable, since there may be shields requiring both voltages. A switch is used to apply power to the board.

Since the intended use for the Picduino is as a base unit for the Rainwater Level Monitor project, an RTC and EEPROM were incorporated on the main Picduino PCB. Because the Picduino can operate at 3.3V the RTC, DS1307 can't be used and has been replaced by the PCF8563 in the design

For software development, several compilers can be used including: OS Basic, MikroBasic Pro, Swordfish and Proton. If you use the 18F25K20 or 18F25K22, then the free Amicus compiler can be used. With the latest updates, PicKit2 will program the 18F25K22, see Tips and Tricks. The18F25K22 is also supported by MPLAB.

The “C” compiler used by Arduino can create compiled modules and then linked from libraries using an Include directive. Both MBP and SF can do this, but PicBasic Pro, Proton Basic, OS Basic and Amicus can't. This feature of the AVR-GCC compiler is one of the reasons that the AVR processor was picked for Arduino and why the Arduino platform is so successful. Our intention is to develop code with Swordfish and OS Basic.  

As an aside, the method of Arduino development is similar to our method described in this site. Compile the code, download it, examine its behavior, then make adjustments to the code and try again. There are code developers out there who use the AVR-GCC to create modules that the uninitiated can use. Most of the hard work is done by those developers. For example, writing code to generate the model train DCC signal is not simple because of the timings involved, but I am sure some developer is out there building a DCC module.

Note 1: The Arduino uses DTR of RS232 to reset the processor for an autoboot. The FTDI cable brings out RTS on pin 6 not DTR so it will not work in autoboot mode. Sparkfun sells a USB breakout board that will work (DEV-09716).

DIMENSIONS:

W: 2.7 in, L: 1.9 in, H: .5 in

SCHEMATIC DIAGRAM:

PICTURE:

Picduino without serial breakout

BILL of MATERIALS:

PCB LAYOUT: