voltage from a temperature sensor,
and determine if it needed to record
or download temperature data.
I concluded I needed a PICAXE-
28X2 for the job. The PICAXE-28X1
had one too few outputs.
Before beginning the design
process, I needed to perform an
experiment. Can I use a single I/O
In the thermometer, the I/O pin
is set high (illuminates the red LED)
to indicate above zero temperatures
and set low (illuminates the blue
LED) to indicate below zero
temperatures.
Since the PICAXE could operate
two different color LEDs with a
single I/O pin, this created the
opportunity to include a new
feature in the microcontroller-based thermometer: It could
record a voltage from the item
under test.
Perhaps I’ll add a pressure
sensor to the circuit in the future,
but since the TVC already has an
analog pressure sensor, I’m in no
hurry. Figure 3 is the schematic of
the thermometer design I came
up with.
For readers who would like to
try making this circuit on their
70 May 2014
; This is the placement of components for the copper mask. The red
lines are jumper wires because the design is only single-sided. Use
three-pin male headers for the analog and programming ports. XT
is a 10 MHz resonator. The two LED displays fit in 14-pin DIPs and are
found at Jameco.com as part number 24782. Voltage is any battery
pack, as long as the voltage is 6.0 volts or greater.
; During a
download, I
programmed the
thermometer to
display dL. This
way, I could
confirm whether
or not the
thermometer
knows its
suppose to be
dumping data.
