SP: Schematics and PCB Design

Once the simulations in Proteus are made and everything is validated, it is time for the final schematic and PCB Design in Kicad

The schematic is shown next:

SP schematic

Everything is as simple as it appears: The pic18LF14k50 is the microcontroller that drives some NPN transistors, which allow the display to light. Same for the buzzer&LED indicator. In this case, we also use an inverter (74LVC1G06GW,125 from Nexperia) so we can control the two displays with one pin... We did that on purpose since we are using 100% of the ports in the PIC. 


In the same way that we made with the Bytes Counter, We have a high-frequency refresh rate to mock the human eye and create the illusion that all of them are lighting at the same time. (Only Engineers know that there is only one at a time! ) 

For the buttons, an RC filter made of 10K resistors and 100nFs capacitors will filter any bouncing effect. This time we also add some diodes so we avoid messing up with the PGD/PGC pins. 

Once the schematic is clear, the components are placed in the top layer of the PCB (to make it easy and faster to manufacturer):

PCB Overall

We ended up with a four-layer PCB in which we route every component:

4 layers

The reason behind this decision is pretty simple: Nowadays PCB manufacturing is quite cheap, saving time of design with the extra space 2 additional layers given to the designer. In fact, The cost-saving of the time is bigger than the increased cost for the PCBs, at least if we are producing our product in small quantities (less than 1000/year). Finally, thanks to our Sponsor, we got the final result:



Thanks for reading, next chapter will be assembly and validation!