Well, here are some examples of how you can use them.
For turning on/off a motor or light drawing more than 600
mA, you will most likely need some power control device
such as a relay. A relay with a coil drawing less than 600
mA and a drive voltage less than 15 volts can be directly
connected to the output of the pill timer as shown in
Figure 9. Don’t forget to include a diode across the relay’s
coil to prevent voltage spikes when the relay is turned off.
These voltage spikes can easily destroy the drive transistor
Q1. The diode is placed with its cathode on the positive
output side of the pill timer so that it is reversed-biased. If
you put the diode in backwards, don’t worry. When you
apply power, the diode will send you a nice little smoke
signal that it’s in backwards. Start over with a new diode.
Another neat device for controlling electrical power
are AC electronic relays that use semiconductors to turn
the power on and off. Electronic relays are very
affordable, are controlled with a DC voltage signal level,
and can switch as much as 220 volts at 20 amps.
Referring to Figure 10, the pill timer requires a pull-up
resistor across its output (1K to 10 Kohms) to generate
the digital control signal necessary to control the
electronic relay. The relay’s positive input is connected to
the resistor on the side of transistor Q1, while the
negative input goes to ground (negative power input,
or -5V on Figure 10). Remember, in this configuration,
the sense of the output is reversed.
Something that many electronic hobbyists want to
control are LEDs. Looking at Figure 11, the LED is
connected in series with a limiting resistor to the pill timer,
making sure the anode end of the LED is toward the
positive output of the timer. LEDs can be strung together
in series using a single limiting resistor, as long as the
output voltage is sufficient. The limiting resistor should
limit current to a maximum of 20 milliamps. Assume each
LED has a voltage drop of two volts. LEDs can also be in
parallel, but you’ll need a limiting resistor for each LED.
One helpful fixture I made for testing the software in
pill timers is shown in Figure 12. It provides easy
connections to the world. Power is provided by a nine volt
battery with an LED to show that power is on. An LED
with a limiting resistor is connected with a jumper plug,
and another jumper plug is
connected to JP1 on the pill timer
to allow easy shorting of the
startup sense. Finally, a six-pin
header is installed to allow the
PICkit 2 to be directly installed,
making for easier software
■ FIGURE 9. Traditional relay connection.
■ FIGURE 10. AC
The files for the three assembly programs and the
circuit boards are available for downloading at the article
link. Readers can make any changes to any of these files
for private use, but may not use any of these materials in
commercial products or for resale.
From a software standpoint, what you can do with a
pill timer is largely limited by your imagination. Although
the program space of the PIC10F200 is small, there is still
a lot of capability to do many things, expanded by also
being able to use a control input signal. But, the neatest
thing about pill timers is their size and being able to stick
them into almost any place with a piece of double-sided
tape. Making little displays for the holidays becomes a
snap, so enjoy this new medicine for curing the headaches
in your projects. NV
■ FIGURE 11. LED connection.
■ FIGURE 12.
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