Jaluino, with user guide, schematics, PCB, shields, etc... can now be reached on the following sites:
Main site: http://jaluino.org
Main site: http://jaluino.org
It's been a while I'd like to build and provide the same kind of board as Arduino's, but PIC-based. And powered by Jalv2 and jallib, of course. The reasons are pretty clear: as we share our jal code (software), why don't we also share our boards & PCB (hardware) ? Jaluino to the rescue !
There can be many benefits having such a board, such a common hardware. For instance, everybody would be able to get a board, and experiment with it (educational benefits). Keeping hardware problems away helps focusing on the real experiment's content. Jaluino provides a base, a context on which anyone can build extra boards. These can then be shared with everyone, easily, since Jaluino is the common base. This is what Arduino's shields are about, and what would be nice to reproduce.
Which PIC should be used for Jaluino ?
The size and the features are what matter. A USB capable PIC is somewhat mandatory, it opens oportunities for nice experimentation. 18F PICs seem to be the candidates. What about these three PICs:
- 18F14K50 : 20-pin, cheap, lots of features
- 18F2550 : 28-pin
- 18F4550 : big fat 40-pin, the max for a PDIP package.
- Jaluino Mini : 18F14K50 based, breadboard layout (no shield connectors, just plug your Jaluino board on a breadboard). Closed to Pinguino, but with a smaller PIC
- Jaluino Medium : 18F2550 based. Board contains connectors on which we can plug shields. A breadboard version can also be built (same as Pinguino)
- Jaluino Maxi : 18F4550 based. Board is "shieldable" too, a breadboard version may not be a good idea, as the PIC is quite big a would require a rather large breadboard.
(we'd definitively need to work on marketing names for "Mini", "Medium", "Maxi"...)
Connectors for shields
Despite several Jaluino boards would be available, shield connectors have to be compatible. Ex: a shield for 18F2550 can be used with a 18F4550 (the reverse isn't true...). As Arduino Diecilima's shields are compatible with Arduino Mega. This can be done by extanding the 18F2550 layout by other connectors.
Comparing 18F2550 and 18F4550 pins, we can see one is perfectly included into the other. In green, pins from 18F2550 which be found in 18F4550, in blue, 18F4550 only pins. Circle-red pins are important features: serial, I²C, USB and OSC. Fortunatly, these are carried by the exact same pins between 18F2550 and 18F4550.
(also note 18F877 could be used and plugged into a Jaluino Maxi as OSC, RX/TX are carried by the same pins as in 18F4550. Only I²C -- and USB of course -- pins aren't compatible).
The general layout for Jaluino Medium and Jaluino Maxi would look like this (not scaled...). Orange connector is dedicated to power supply. Green connectors are exactly on the place between Maxi and Medium Layout, these are the compatible pins. Blue connectors export 18F4550 pins only.
Several other connectors would be needed:
- USB, of course...
- I²C : following Joep's suggestion, a 5-pin header (+9V,+5V, GND, SCL, SDA) can be used a dedicated connector, making easier connection between boards & other parts using this protocol
- Serial : again, following Joep's suggestion, a 4-pin header (+5V, GND, TX, RX) would allow to plug any serial module (see later)
- ICSP : to easily program the chip, even if no bootloader is present
Serial : different options
In addition to dedicated USB connector, a serial connector would allow easy comms. from Jaluino to the external world. But what type of connector to provide ? DB9 ? USB via USB-to-serial conversion ?
Here are the different alternatives, depending on budget limits, easiness to make, and parts used to build this module:
- USB-to-Serial via FDTI chip: widely parts, but FTDI chip only exist on SSOP package, hard to solder (but not impossible). Small. USB can be used to power the board.
- USB-to-Serial, using a 18F14K50 : easy to make (though 18F14K50 may be quite hard to find...). Size to define. USB can be used to power the board.
- DB9 connector, using MAX232 chip : classical, quite big. External power supply will be required
- what-you-want option: just plug a module which honor the connector's interface. For instance, I have a bluetooth-to-serial module, this gives the opportunity to easily integrate it to Jaluino.
Few words about bootloader
ICSP connector make the develop-program-test cycle faster, preventing unplug/plug the chip to program it. But still it requires a programmer... A bootloader is required here.
There are many different ones out there, but Tiny Bootloader is widely used, very (very) small, many different programs exits for many different platforms. Bootloader should be able to be triggered without having to manually reset the device (see here for more, it seems to require some hardware parts).
A first schematic
I started to build a schematic. Please keep in mind this is very alpha, and this is not even supposed to work...
Following Arduino, I'd like to release Jaluino schematics & PCB under Creative Commons Attribution-Share Alike 3.0.
Basically, it says:
- Attribution — You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work).
- Share Alike — If you alter, transform, or build upon this work, you may distribute the resulting work only under the same, similar or a compatible license.
Any suggestions ? Would you like to join the effort ?
PS: see this thread on jallib group for a discussion. Also search the group more...