The 3. 5 mm jack which I used for the project requires
that the sense board be mounted with small right angle
brackets and holes drilled in the dryer back panel for the
jack, as well as the mounting screws. Plastic brackets were
fabricated and holes drilled to enable mounting. Other
jacks with threaded barrels can simplify mounting. Figure 7
shows the sense board mounted to the back panel, with
the current sense transformer in the foreground.
A two-conductor plus shield cable connects the sense
board to the main board. There is no electrical connection
to the shield at the dryer to avoid potential ground loops.
Be mindful to connect the cable wires so that the
collector of the transistor on the sense board connects to
the signal input of the main board. The shield should
connect to the common of the main board.
The Dryer Minder board is mounted next, external to
the dryer. I use a shaped plastic plate with clearance for all
parts and connectors of the main board. I recommend
mounting the main board so that the Heartbeat and Run
LEDs are easily seen. Connect the five volt power supply
to the main board.
With the main board powered up, the Heartbeat LED
should be seen to briefly flash each second. Start the
dryer; the Run LED should flash in tandem to the
Heartbeat. At 20 minutes less four seconds, the Minder
should beep, alerting you to check the lint trap.
This project lends itself to many other applications
besides green technology. Since the easy to edit C code
includes serial output via the PIC USART Tx pin, display or
telemetry applications are plentiful. For example, a running
total of on time for a machine or appliance could be easily
implemented using a serial LCD for display, such as the
SparkFun LCD-09395 which was used during development.
By decreasing the USART data rate, the SparkFun WRL-
10534 and WRL-10532 can be used for remote telemetry.
I use these for wireless control of a fan system.
An alternate telemetry application would be to sense
open and close times of a remote gate. The PIC has rich
analog input, such as for sensing current of water heater
elements or temperature with an analog temperature
sensor. Port C — used for the Heartbeat and Run LEDs —
has two additional inputs/outputs that can be used for
alarms, moisture sensors, and other peripherals.
Whatever the application, interference with the real
time clock (one second counter) connected to pins 2 and 3
or the ICSP header connections should be avoided. Be
careful to not push too much code into either the interrupt
handler (used by the clock) or the main loop. I found that
longer messages to the serial display could have timing
issues at the default (9600) baud rate of the serial display
when using un-optimized code. If you need more
component room for expansion, All Electronics sells a larger
solderable breadboard suitable for more advanced projects.
What do you have in mind for this circuit? NV
32 April 2014
; FIGURE 7.