HEllo world! Do you have any suggestions about the way to realize a PCB including an MBED? Do you know where i can find them if it already exist? For example, Do i have to put a ground plane just below the mbed to protect the mother board from EMI/radiating fields? Do i have to reduce inductive effect from ground bounding? Unfortunatelly there is only one ground connection What is the reference of the DIL/DIP socket where is plugged the MBED as shown in a picture of the BLOG? Many thancks

Raphael

Well as far as the socket goes, I think you can use two 20 pin SIL sockets. By the look of it I think a SAMTEC SSQ-120-01-G-S is suitable, available in the UK from Farnell, stock code 1668320. You will need two of these and they are for through-hole mounting, rather than surface mount (I intend to use them on stripboard). Not 100% sure, but I'm about to buy some so I'll let you know if they don't work.

It is possible to find DIP sockets with the required 0.9" spacing, though they are not too common. And they don't seem to come in 40 pin sizes.

You could use something like the Mill-Max 110-43-950-41-001000 http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=ED90046-ND, and trim 5 pins off each side to get it down from 50 pins to 40 pins.

Hi..

to mount an mbed, the easiest option is these from rapid. (a pair of the 20 pin ones) (Rapid Part 19-0088)

https://www.rapidonline.com/productinfo.aspx?&tier1=Cables+%26+Connectors&tier2=Connectors+-+Multipole&tier3=PCB+Interconnect&tier4=Single+row+PCB+sockets+-+2.54mm+pitch&moduleno=180585&catref=19-0088

There is an mbed eagle library on this site that has the layout for a pair of these correctly spaced apart to from an mbed socket.

Thanks David. You just saved me a lot of money. Please ignore my suggestion of the SAMTEC connectors. They are much more expensive.

Samtec are pretty good for providing free samples of connectors look here. If you ask nicely they might give you some freebies?

Hi Raphael,

Laying out a PCB for an mbed is pretty straight forward - of course it depends mostly on your needs. There are several baseboards listed on the Cookbook page. Scan about 1/2 way down. If you follow the link for them, you will see that some appear to have a ground-plane and others do not.

With respect to the need for a ground plane, this depends on many factors. A few of which are:

• What is the electrical environment your project will be in? If there is a lot of EMI/EMC concerns, then a ground plane can help, as can other circuit design techniques.
• If the concern is with EMI and EMC, can you put your project into a metal enclosure to shield it and the outside world from each other?
• Will your motherboard have a lot of very sensitive circuitry on it? Then a ground plane can help, and isolating the sensitive circuit as much as practical will also help.
• You've probably seen many schematics and devices with small capacitors near each part. These typically straddle from power to ground, or filter noise from input circuits - steering high frequency noise into the ground path.
• Will your project switch a lot of current, or be exposed to high current pulses? Then isolate the high current from the rest of the power distribution as much as possible. Also, create wide circuit traces to help manage those currents. Here too a ground plane can help.

So, there's not any easy answer, but multiple techniques applied together can usually overcome the issues. Among the important choices are applying appropriate circuit design techniques.

As you know, the mbed has a single ground. In many designs, the mbed will not be switching very high currents, beyond its own internal needs, but one place where this single power and ground could have an undesired effect is with the analog inputs. The processor itself has separate power and ground connections for the analog signals, but these are brought together with the main power and ground on the mbed. So, switching current and noise on these power lines could affect the analog measurements.