An inexpensive perf board was used for the
prototype. This is cut to size to fit in the limited space of
the control panel. The sense board connects to the
current transformer with the two pins on the lower far left.
Output to the main board is through the 3. 5 mm jack.
The sense board is shown in Figure 4.
The Dryer Minder main board is next. The circuit
diagram is shown in Figure 5. J1 is the sense input from the
sense circuit. The oscillator crystal for the low power clock
is seen connecting to pins 2 and 3. The Run and Heartbeat
LEDs connect to pins 8 and 9. The beeper is switched
through the PIC2N3904. J2 pins are used to activate test
mode, and J3 is the serial output connector for test use.
The code for the PIC is available at the article lnk. The
program was developed using the HI-TECH
C compiler/Pro edition in free mode.
Note the few locations where traces
need to be cut. These are identified by the
thick black rectangles in the layout
diagram, such as near the Run and
Heartbeat LEDs, and the J3 (serial
out/debugging) connector. The area to the
lower right is intentionally left bare for
future expansion. Refer to Figure 6.
Programming is through the ICSP™
connector. I programmed the PIC using a
PICkit 3. Once the program starts to run,
Jumper J1: This condition simulates an active low from
the sense board, as would occur during “dryer on.” The
Run LED will light every time the Heartbeat LED is on
when J1 is jumpered/set low. If you have connected the
serial LCD to the serial output (J3), the count in seconds
will appear on the display while in Run mode.
When leaving the connection to the PICkit 3, the
PICkit 3 causes RA0 to be pulled low, activating Test
mode. The beeper will sound 16 seconds into the test
cycle if the PICkit 3 is still connected and there’s a jumper
30 April 2014
; FIGURE 5.
; FIGURE 4.