Schematic 3 represents a simple PIC implementation
that is supported by a CP2103. The Microchip hardware
behind the CP2102 is shown in Schematic 4. I have
chosen to use the PIC18LF4620 as it supports multiple
timers, numerous communications protocols, and lots
of I/O. The LF in the PIC part number tells us that the
PIC18LF4620 can also operate efficiently with a 3. 3 volt
power rail. Just in case you need to run your PIC and
peripherals at 5.0 volts, I've designed in a jumper to allow
you to use VBUS (+ 5 volts) or VDD ( 3. 3 volts) to power
the PIC. Both the CP2102 and the CP2103 I/O and UART
are five volt tolerant.
ASSEMBLING THE UNITS
You can only purchase a CP210x IC in the QFN- 28
package. So, in keeping with the intent of the QFN
package, at every opportunity we'll design in SMT
components. I realize that many of you have access to
1. ALL DISCONNECTED PIC PINS TERMINATE AT HEADER
2. ALL RESISTORS 0805 SMT PACKAGE
3. ALL CAPACITORS 0805 SMT PACKAGE
SMT soldering and rework equipment. I also realize that
most of you probably don't. I want to be sure that any
Nuts & Volts readers with reasonable soldering skills can
assemble these projects. So, to prove that manual SMT
soldering can be used, I'll assemble both projects using
common sense, SMT soldering techniques that you can
easily understand and apply.
The solder sides of a CP2102 and CP2103 are under
the lens in Photo 1. If we can get the CP210x on straight,
the rest of the assembly process will be a walk in the park.
Normally, I would use a stencil to lay down the solder
mask for a part like this. Following a highly magnified
precision mounting process, I would run the fully stuffed
PCB through a batch oven. However, in that you may not
have a batch oven and a precision rework station, we'll
mount the CP210x parts the cheap-and-not-as-easy way.
There are many ways we can manually mount and
solder the CP2102 and CP2103. No matter which project
variant you decide to build up, to make the job easier
■ SCHEMATIC 3. Note
that the only hard data
the CP2103 and the
PIC18LF4620 are limited
to the TXD and RXD pins.
As long as you supply the
UART code on the PIC
side, you can substitute
any PIC that you desire
behind the CP2103.