Title: Free PCB build - PICkit3 clone on QFP prototyping board
Post by: hlipka on January 22, 2014, 02:50:37 pm
Post by: hlipka on January 22, 2014, 02:50:37 pm
I finished this a while ago, and promised (http://http://dangerousprototypes.com/forum/viewtopic.php?f=2&t=5719#p53582) to write about it...
I got the 0.8+0.5mm xQFP protoboard (http://http://dangerousprototypes.com/store/index.php?main_page=product_info&cPath=24&products_id=195&zenid=mo9t3n43d9n6td8v5gm72u66i5) from the Free PCB drawer. Since I wanted to get a PICkit3 for a while, this looked like a perfect fit. So I looked up the schematics, ordered what I needed, and started work.
[attachment=0]
It took longer than expected, and in the end I had just one silly mistake costing me about two months looking for it (just two swapped wires:( I did write a complete description of the while PICkit3 clone project (http://http://blog.hendriklipka.de/archives/2014/01/pickit3_clone.html), including more images and the complete schematic I used in the end.
So, what about the protoboard? After all, this was not just a prototype but a real, complete project.
I like that it has a large number of different footprints and connection options available.
But if they are not used, they are just in the way. I did not use the SSOP footprint,
and it takes much room. The footprint for the crystal was on the wrong side of
the QFP footprint for me (one needs to be lucky to have it at the right place).
Having the footprints for the push buttons in the middle of the board means
they are most likely covered by wires. So maybe they should go further to the edges.
This would also move the prototyping area more closely to the QFP footprint.
Maybe it should go to the center, with all the other stuff around it. There
might also be space to save by not using through hole connections for all parts. Maybe
just using SMD pads for connecting wires to the crystal can reduce the overall
footprint in half, without sacrificing usability.
One thing constantly ticking me off was that the numbering on the QFP footprint
differs by side. Since the MCU comes in 0.5 mm pitch (as do most QFP parts I found)
it goes to the bottom side of the PCB, whereas anything else goes to top. But there
the layout is reversed, so Iavoided looking at the printed QFP pin numbers and
always needed to count in reverse. Thats really annoying. Next time I would rather
use the single-footprint version of the board just for that reason (even if it
comes without USB footprint).
I liked the availability of a 3.3 V power rail in all the different places around the board.
But since the PICkit uses different voltages (3.3V in some places, and a switched
voltage rail called V<sub>DDint</sub> in other places) I could have used a second voltage rail.
I suppose the same might be true for other projects, needing 5 V and 3.3 V.
I got the 0.8+0.5mm xQFP protoboard (http://http://dangerousprototypes.com/store/index.php?main_page=product_info&cPath=24&products_id=195&zenid=mo9t3n43d9n6td8v5gm72u66i5) from the Free PCB drawer. Since I wanted to get a PICkit3 for a while, this looked like a perfect fit. So I looked up the schematics, ordered what I needed, and started work.
[attachment=0]
It took longer than expected, and in the end I had just one silly mistake costing me about two months looking for it (just two swapped wires:( I did write a complete description of the while PICkit3 clone project (http://http://blog.hendriklipka.de/archives/2014/01/pickit3_clone.html), including more images and the complete schematic I used in the end.
So, what about the protoboard? After all, this was not just a prototype but a real, complete project.
I like that it has a large number of different footprints and connection options available.
But if they are not used, they are just in the way. I did not use the SSOP footprint,
and it takes much room. The footprint for the crystal was on the wrong side of
the QFP footprint for me (one needs to be lucky to have it at the right place).
Having the footprints for the push buttons in the middle of the board means
they are most likely covered by wires. So maybe they should go further to the edges.
This would also move the prototyping area more closely to the QFP footprint.
Maybe it should go to the center, with all the other stuff around it. There
might also be space to save by not using through hole connections for all parts. Maybe
just using SMD pads for connecting wires to the crystal can reduce the overall
footprint in half, without sacrificing usability.
One thing constantly ticking me off was that the numbering on the QFP footprint
differs by side. Since the MCU comes in 0.5 mm pitch (as do most QFP parts I found)
it goes to the bottom side of the PCB, whereas anything else goes to top. But there
the layout is reversed, so Iavoided looking at the printed QFP pin numbers and
always needed to count in reverse. Thats really annoying. Next time I would rather
use the single-footprint version of the board just for that reason (even if it
comes without USB footprint).
I liked the availability of a 3.3 V power rail in all the different places around the board.
But since the PICkit uses different voltages (3.3V in some places, and a switched
voltage rail called V<sub>DDint</sub> in other places) I could have used a second voltage rail.
I suppose the same might be true for other projects, needing 5 V and 3.3 V.
Title: Re: Free PCB build - PICkit3 clone on QFP prototyping board
Post by: ian on March 20, 2014, 08:33:39 am
Post by: ian on March 20, 2014, 08:33:39 am
Cool, and thanks for your feedback!