I turned using 0.1 pitch headers on each PCB, but this was totally inefficient, because this connector occupies more PCB space than the PIC itself. Taking also into account that the programming connector will only be used once, i decided to design something better, smaller and somehow faster for programming the PICs.
Pogo pins are here to help
I did not know the existence of pogo pins until i saw one interesting make from Limor, our beautiful engineer from NY. These pogo pins are called "pogo pins" because they are spring loaded. They have electrical conductivity between their two parts so they can be used as connectors.
The idea is simple: i will make an eagle library with the ICSP device which will actually have 5 pins, the MCLR/Vpp, positive and negative supply, and the serial Data and Clock pins. These are actually the 5 wires that the ICSP wire has. The package of this eagle device will be SMD of course, so that it will occupy only one side of the PCB (and not two like the through-hole connector), and it will have 0.05 pitch instead of 0.1 to further reduce the footprint:
You can download and use this Eagle library yourselves from the following link:
I actually bought two different sizes of pogo pins for test, the big one had diameter 1.36mm and the small one had diameter 0.68mm and length 16mm. This is the size that fits my needs best (for the 0.05 pitch).
For the PCBs, i only had to print onto the copper the corresponding footprint for the pogo connector:
The pogo connector PCB
Now i had to make a PCB for the pogo pins. The PCB must have one 6 through-hole female connector for my PICKIT3 ICSP wire on one side, and the 5 pogo pins on the other side. One additional trick that i did is that i did not soldered the pogo pins all at the same height, instead their endings are inclined. I did this for easier placement onto the PCB, since the pins are touched one-by-one on the PCB rather than being touched all at once:
And here are the Eagle files for this PCB:
Keep in mind that the pitch is 0.05 which is rather small, and the pads are also very small. Soldering the pogo pins onto the PCB might be hard since they must be soldered parallel to each other and on one plane. You may wanna make 3 PCBs, one wto use for the connector and the other two for aligning the pogo pins during soldering.
Holes for aligning the pins... (Update May 21 2012)
I'm not a surgeon to have a steady hand. I would rather say that i am some sort of blacksmith in terms of hand stability. Therefore, i made another library for the PCB ICSP pads, and instead of SMD pads i used through-hole pads. I do not intend to drill those holes, i use them only for aligning the pogo pins. This idea works perfectly fine. As a matter of fact, i already used this connector to program 12 high power LED controllers for a project of an artist from puplik.org
And here is the new library file to download and use:
Continue reading. Click here to view the references.