DiscoverCircuits.com -- Hobby Corner
Last Updated on:
Tuesday, April 01, 2014 04:34 AM
Hobby Circuits'
Category List
The contents &
graphics of Discovercircuits.com are copyright protected.
LINKING to Dave's circuits is permitted but DO NOT COPY any files to your WEB
SITE server |
|
|
|
|
More |
Poor Man's
Timer
Aug 24, 2008
designed by David A. Johnson, P.E. |
Often during testing of certain
equipment and components, you would like to keep track of the elapsed time in
hours, minutes and seconds. There are some nice commercial digital timers and
counters available for just this sort of application. However, although it
may not be as accurate, there is a cheaper way to go. I’m sure many of you
have some old wrist watches or battery powered dial faced alarm clocks collecting
dust in some drawer. |
|
With just a bit of effort you can
turn these into value pieces of test equipment. You must use the analog clocks
and watches with dial faces and not digital types, since the analog devices retain the
elapsed time information, even after the power is interrupted. With a wrist
watch that has a day/date feature, you can time things up to 31 days, to an accuracy
of a few seconds. |
Most wrist watches are powered by 1.5v button cells while many dial
face alarm clocks are powered by 1.5v AA or AAA cells. These timing devices draw
very little current and can easily be wired into an electronic circuit. The
circuit might be connected to a microprocessor or some sensing device. When
power is applied to the clock, the elapsed time is recorded. When power is
turned off, the elapsed time information is retained.
To convert these devices into a timer,
first open the back of the watch or the battery compartment of the clock.
Remove the battery. File a 1/8 inch wide by 1/16 inch deep notch into the
metal of the watch case or the plastic of the battery compartment lid. Next,
solder two wires onto the battery contacts. |
[H-Corner/ads/i-HC-boombox_adsense.htm]
|
|
Use a thin red wire, about 12 inches
long, for the positive side and a darker color, such as black, for the negative
terminal. If you have difficulty applying solder the clock’s battery contacts,
you can first press some adhesive copper tape onto the contacts, then solder the wires
onto the tape. Route the two wires through the notch. Then close up the back
plate or compartment. That is it. You are now are ready to time something.
|
|
|
Watch Face |
Clock Face |
|
|
|
Watch Back |
Clock Back, Battery Removed |
|
|
|
Notch Filed in Watch Case |
Wires Soldered to Battery Contacts |
|
|
|
Wires Soldered to Battery Contacts |
Wires Routed Through Notch |
|
A simple voltage divider circuit can
be used to convert the +5v logic signal from a computer or a logic device into a 1.5v
signal, to power the clock. I suggest a capacitor be included, to provide the
needed peak current pulse needed by the clock’s solenoid. |
|
Click on Drawing Below to view PDF version of Schematic |
|
What might you use this thing for?
One application might be to time how long a door remains open during the day or week.
Maybe you could use it to time how long a battery can power a device or maybe how many
hours a computer is being used per month. I will later show how this simple
device can be used to measure the milliamp-hour capacity of a button or coin cell
battery. |
|
More
Hobby Circuits'
Category List
eMail David A.
Johnson, P.E. about this circuit |