system as shown in another manual in the Project Gallery
— PIC18F4620 Cookbook, Hands-on Experiments, page 69:
"Minimum Circuit Schematic: PICkit™ 2 programmer &
18F4620." Many of the bit-banging examples would work
with other chips in the 18F series.
Thomas Henry hit that nail on the head when he said
"Datasheets for PICs run in the hundreds of pages and
aren't necessarily organized for best learning." I wrote
these notes as I constantly turned back and forth through
the 500 plus pages of several Microchip datasheets, trying
to get any PWM to show up on my scope. My notes
include numerous page references to Microchip
datasheets to help the DIYer get into these complex
documents. A You Tube video exhibits some of these
experiments at www.youtube.com/watch?v=
As a long time reader and subscriber to Nuts & Volts,
I included a tribute to “Smiley” Joe Pardue in the
Cookbook page 77, using the WDT to cycle cylon eyes.
Thanks for the note and the information for N&V
readers. Obviously a labor of love.
I am writing to say that I read the article by Robert
Reed (Construction of a Low Budget 180 MHz RF Sweep
Generator) in the December 2013 issue with interest
because I have been trying to get more and better output
from my Heathkit IG5280 with no success to-date. I plan
to build this project using surface-mount parts and wind
my own coils.
I want to comment on the article by Robert Atkinson
(Improved Efficiency 13.8V Power Supply) in the February
2014 issue. I applaud the way he gives the rational for
selection of components and tips on construction. I think
the author should have mentioned that the MOSFET
turn-on voltage Vgs(on) should be matched. Otherwise,
one may hog all the current and defeat the purpose of
paralleling. If all the MOSFETs are from the same batch,
they likely will be matched.
Use a Crowbar
The 13.8V MOSFET Power Supply article in the
February 2014 issue was great! There is something missing
from the design, however. If there is a failure that results in
an overvoltage — such as a shorted FET — then the raw
DC will appear at the output. This could be a disaster to a
high value load like my ham transceiver. A crowbar circuit
should be added to quench the supply and blow the fuse
so the load is protected.
Thank you for your comments. A crowbar circuit was
considered, but I felt it wasn’t necessary. This is because of
the very conservative rating of the MOSFETs and the low
unregulated voltage. A bipolar design typically has a 19V to
21V transformer giving a unregulated voltage of 26V to
29V. As you say, a failure of the (often under-rated) pass
transistors could be very damaging. The 15V transformer in
the MOSFET design would give an unregulated output of
20V — much less likely to cause damage. However, if you
wish to add a crowbar, a conventional circuit using a zener
work just fine.
Take a look at
March 2014 73
PIC Basic Project Board
16F88 PIC Basic Project Board Features
* LCD Display - back light & contrast control
* 2 A/D channels, 8 digital I/O lines, 5V and 9V operation
* Free student version of PICBASIC PRO & Microcode Studio
with purchase of PIC Programming book bundle.
16F88 Programming Service Available
* Project library with source codes and hex files available.
See 16F88 PCB Project page for more details
Bend and Force Sensors
CdS Light sensors
Radiation Pulse Counter
Images Scientific Instruments Inc.