BoB3 - mbed on Stilts
A while back I offered to do some mods to BoB2.
I soon realised that BoB2 did not really meet my needs. I liked that it took care of the "awkward" interfaces like micro SD and Ethernet, but I saw little value in the PWM headers and switches. It was missing what I really liked about mbed, namely that I could plug it into a breadboard and do more or less anything with it.
I then had the idea of making the mbed socket a stackable header so that the breakout itself could be plugged into a breadboard with the same footprint as mbed. The result is BoB3. Tongue in cheek, I call it mbed on stilts.
The main features of BoB3 are:
- Micro SD card socket
- Coin cell battery holder for RTC battery (takes 1216 through 1225 size batteries)
- Ethernet MagJack with LEDs
- USB type B socket with ESD protection
I have connected the MagJack LEDs to some mbed pins via a DIL switch. Each LED can connect to one of three mbed pins; the idea being that (hopefully) one of them will not be used by your application. According to the mbed schematic, the PHY LED pins connect to LPC1768 pins 39 and 40. What I have in mind is a simple routine running off a Ticker to copy the state of those pins to the MagJack LED pins. If the ticker runs at 10 - 20Hz, the MagJack LEDs should appear live.
To avoid stubs, the header pins for the Ethernet and USB signals will be cropped and will not insert into the breadboard. All the other header pins will insert into the breadboard.
Most of the onboard circuitry is SMD. It had to be given the space constraints. I have deliberately chosen large (0805) passives and a coarse pitch (50 mil) USB protection diode chip so that, given reasonable care, the board can be hand soldered.
The placement and layout are shown below:
I have placed an order for a small quantity of bare boards with PCB Pool. As soon as I have built and tested the boards, and assuming there are no problems, I will post the Eagle schematic and layout files here.
Update 26 Jan 2010
I have now received the bare pcb's from PCB Pool and have made up one board. Here are some photo's:
The next step is to test it. I will then post the Eagle files and some assembly documentation.
Paul
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BoB3 - mbed on Stilts
An mbed breakout board that retains the DIL form factor
Page owner: 
Paul Griffith
Created 24 Dec 2009.
Last updated 26 Jan 2010
Hi Paul,
Good stuff, I really like this concept.
Have you got any boards back yet? Is it all working as you'd hoped?
One thing that occurred is that rather than posting the Eagle files, would you consider uploading it to BatchPCB.com and publishing it? As the design owner you'll have the fun of ensure it meets thier DRC and so on. Once that is done, you can post the URL of the published design and then anyone can buy your PCB just by clicking the link and making an web purchase like any other. Slick!
Cheers,
Chris