⇒ Microchip PIC-Based Resistor Checker
⇒ In my basement lab, I have racks of
components including a large plastic
draw cabinet full of resistors. When I
order new resistors, it becomes a
tedious job of cutting the resistors from
their tape and reel packaging and then
placing them in the proper plastic drawer. It’s one of those jobs I would like to
hand off to my eight-year-old daughter.
She often comes down to see me and
asks if she can help me with anything. It
seems I always have some clean-up job
to do, but that isn’t very exciting.
Then I thought about having her put
these resistors away for me. The catch
is she doesn’t know 10K from 10 ohms.
Add to that the color coding and the
whole thing gets too confusing. Then it
occurred to me, why not let a PIC micro
A/D port read the resistor and light an
LED next to the plastic tray where the
resistor could be stored. This would
reduce the job down to picking up a
resistor, placing it across two probes,
and then putting it in the tray where the
light is lit. That is something she is
more than capable of handling and
might even be fun for a while.
This article describes this project and
shows how easy it is to use the A/D
port with the PICBasic Pro compiler. In
fact, I was able to write the code within
31 commands so this could be done
with the sample version of PICBasic
Pro which you can download from
www.melabs.com for free.
72 February 2006
by Chuck Helllebuyck
Iwill use a PIC16F876A for this
project which is overkill since it has
22 I/O, 8K of memory, and five A/D
ports. The reason I selected it is for
three reasons: 1) the sample version
works with this chip; 2) I have tons of
them lying around; and 3) I may want
to expand this setup to measure other
components, such as a capacitor
tester and seven-segment LED
display tester to check for common
anode or cathode, and who knows
what else I can come up with. With
the 16F876A, I have all the I/O and
code space I will need.
The trickiest part of the project
was to get a set of probes that were
easy for her to use. I decided to build
two “Y” shaped probes that would fit
into a breadboard, as seen in Figure
1. This allows her to set the resistor
in place and then let go. Very little
current will run through the resistor,
but having her set the resistor down
in the probes and
let go makes her
mom more comfortable that she isn’t
going to be electrocuted by one of
dad’s creations. It
also makes it easier
to prevent her
fingers from getting
in the way of a
connection.
I made this
⇐
FIGURE 1. Y-shaped probes in a
breadboard.
