PCB layout

A project log for RPNCalc

A calculator which uses RPN instead of infix notation

raphael.treccanichinelliraphael.treccanichinelli 04/22/2019 at 11:210 Comments

i began my PCB layout by creating a footprint for the screen. the 'correct' method would be to create a part in altium, but since this part consisted of just 4 mounting holes and a header, i decided to use a header part and 4 Via holes, and just lock them in place.

that set the width constraint for the design, so my next step was to arrange the buttons. 

I made sure to hide the ref-designators under the button area, so as to keep the silkscreen clear for the button functions (in the screencap they are all SWX_1 because i copied the buttons to a blank area of the screen)

I then arranged the components roughly on the board. Note the light blue traces are on the bottom side of the PCB, and the red holes are plated vias from top to bottom. 

I wanted to keep all the components on the bottom face, so that the battery would fit in the gap between the screen, to keep it safe. 

i then fit the smaller passives around the device, and began routing. there was nothing incredibly eventful about the routing, bar the fact that i realised i would need a way to flash a bootloader to the Atmega (bootloaded Atmega's are super expensive, and i might try using optiboot). To that end i had to add a single pad, as most of the bootloading pins are broken out over the screen connection. I should hopefully be able to bootload the Atmega without too much stress. 

when laying out the silkscreen, I took care to ensure the text was centred around the middle of the switch. I had to get creative with some of the symbols, the altium silkscreen text seems to only support certain character sets, so the root symbols are actually comprised of a few segments of PCB trace, shifted to the overlay layer.

I originally was planning to use OSHPark to order these PCBs, but in the end i went for PCBWay, due to the lower cost and better selection of copper mask colors. I picked black with white silkscreen, and used all the other default options for substrate, thickness, coating, etc.. 

I'm impressed with the level of detail that seems to be present in their production process, they have a tracker online that informs you exactly where your PCB is in the factory.

How accurate that is remains a mystery, but its a neat feature nonetheless. I paid $22 for 5 PCBs, and shipping options varied from $6 for delivery in around a month, through to $21 for fast shipping via DHL. PCBs are set to arrive tomorrow, I'll upload some photos then!