PIC18f4550tqfp Prototyping Breadboard

A typical prototyping breadboard designed around the PIC18f4550 tqfp processor.

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My first attempt to make a "professional" pcb. I've had a few PIC18f4550s in the TQFP format laying around for a bit - that plug into nothing. The chip family is great for quick USB-enabled devices, so I did a layout to put these to use.

The design wires a standard rectangular 44-pin breakout on the top layer to forward MCU pins to a prototyping area. Within the footprint of the breakout rectangle, circuitry to implement basic core functions of the MCU is built onto the bottom layer to maximize board space.

So, here's the design (with plenty of vias). Pads for power caps, external clock, I2C pull-ups, vUSB cap, 2 leds, pull-ups on 3 random pins, and a convenient header for the TQFP's "Special ICPorts".

The double-sided prototyping area has various power buses and through-hole pads. A PCF8574 can drop in easily w/ nearby breakouts for 8 SOT23 N7002s. The proto area also experiments w/ some pads for smd passives (0603,0805,1206).


C1,C2 - Power caps (between VDD and VSS)

X1 - External oscillator

C4,C5 - Caps for external oscillator

R3 - ICSP Pull-up

R1,R2 - I2C Pullups (RB0, RB1)

C3 - Cap for Vusb

R4-6 - IO pin pullups (RD4, RD5, RC7)

led1,2 - 0603 led/resistor pair (RD6, RD7)

Some general notes:

I've mostly settled in on this PIC chip family for USB gizmos that need a 8-bit-lifting capacity. This layout was made with a few specific projects in mind that are likely to derive from a common hardware set. The design philosophy is based on using an I2C port expander to handle load switching (matched w/ transistors if desired) and reserving I/O pins for data exchange and analog sensors.

The TQFP package includes non-typical "Secondary ICPorts" that can be used for in-circuit debugging and programming - freeing all of the 4550's standard pins for IO while still allowing connection to a programmer/debugger. This board design provides an easy-access header for the NC pins.

The SOT23 pads are a double-sided design with breakout pins for Source, Drain and Gate. They're wired up for 2N7002 transistors - and should work with any transitor having the same package/pinout. I decided to save myself some wiring and drew a trace between the source pins of each package, which means that both transistors on a top-bottom pair will have to use the same voltage source.

Integrating SMD pads on the board is a complete experiment. The pads created integrate standard SMD footprints (0603,0805,1206) with a round wiring pad hopefully to allow jumping between smd devices or out to hole-through pins. The extra space on the bottom-side not needed for MCU accessories was used to make an experimental "SMD playground" with a handful of pads and two linked external break-out pins. Time will tell if any of that is useful.

Anyways. The fab apparently didn't choke on the gerber files ... so I guess we'll find out if this sucker works.

  • Boards are back!

    Kent08/27/2015 at 16:37 0 comments

    So ... they have arrived. Oooh. Very shiny!

    Unsurprisingly, the bulk of the time was spent waiting for the mail.

    I plan to populate one over the weekend and see if it works ... or if I messed something up.

  • Designs are off to fab.

    Kent07/28/2015 at 03:14 0 comments

    I made Gerber files and sent them off to somewhere in China ... should have boards back in two weeks or so.

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