Jaluino Medium 18F2550-based: first draft

Jaluino, with user guide, schematics, PCB, shields, etc... can now be reached on the following sites:

Main site: http://jaluino.org
Repository: http://jaluino.googlecode.com
Group: http://groups.google.com/group/jaluino

Careful, schematic and PCB in this post aren't tested yet. Except if you're a daring risk-taker, you shouldn't build this board as it would only be a waste of time, and probably of money too... You've been warned.

I'm still on this Jaluino board.

While trying to get a working schematic, I've also spend a lot of time drawing the PCB. I focused on a 18F2550 version, instead of big fat 18F4550, so PCB layout is simpler and I can focus more important issues for now. So this is now about Jaluino Medium (18F2550), not Jaluino Maxi (18F4550). BTW any ideas about "marketing" names to replace Mini, Medium and Maxi ?...

Last schematic contained lots of errors, mostly on USB and dual power. Luckily Guru Albert helped and provided me four options. I kept the simpler one (I can understand), which consists in having a jumper to select whether power should come from:

• external supply (jack)
• USB self-powered connector

(I would even add a new source of power: from serial, and more specifically from a USB-to-serial converter)

The current schematic seems to look better (yet still untested, this will be for other posts).



So here how the PCB looks like now...



This PCB is expected to be 8.1cm x 7.1cm (3.2in x 2.81in). Compared to an original Arduino (6.9cm x 5.4cm), it's a little bit bigger. But it's also a single side board, and there are lots of other connectors (I²C and serial) not present in Arduino.

There are several connectors. Some will be the shield connectors (JP1, JP2, JP4, JP5 and POWER), female headers as in Arduino, others (ICSP/JP6, I²C, serial) will be male headers.

The shield is expected to be something like 4.8cm x 5.8cm (1.9in x 2.3in). Original Arduino's shield is 4.9cm x 4.3cm. It's a little bit bigger, and I may adjust connectors (move JP1 & JP2 lower) to have a "more squared shape".


Next posts will be about testing and prototyping this board, using a breadboard. This will also be a good exercise to have basic (and maybe advanced) experiments using jalv2 and jallib.


Sébastien Lelong

Jaluino: an Arduino-like board, power by jal

Jaluino, with user guide, schematics, PCB, shields, etc... can now be reached on the following sites:

Main site: http://jaluino.org
Repository: http://jaluino.googlecode.com
Group: http://groups.google.com/group/jaluino

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.
  

Following Arduino's ideas, several Jaluino boards could be provided:

• 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.

PIC 18F2550


PIC 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.


Other connectors...

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...




License

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.

See here for more details.


Any suggestions ? Would you like to join the effort ?


PS: see this thread on jallib group for a discussion. Also search the group more...



Sébastien Lelong