Electronic Circuits and electronic circuits, electronic schematics plus an extensive resource for hobbyists, inventors and engineers

DiscoverCircuits.com, has 45,000+ electronic circuits, cross-referenced
into 500+ categories.    We have searched the web to help you find quick design ideas.
We make every effort to link to original material posted by the designer. 
Please let us if you would like us to link to or post your design.

HOME Schematics Index Hobby Corner Dave's Circuits Electronic Resources Contact Info
Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches


DiscoverCircuits.com -- Hobby Corner
Last Updated on: Thursday, November 30, 2017 07:42 AM

Hobby Circuits 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

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. 

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.

 

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.

Click on Drawing Below to view PDF version of Schematic



Hobby Circuits List
eMail David A. Johnson, P.E. about this circuit


HOME Schematics Index Hobby Corner Dave's Circuits Electronic Resources Contact Info
Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches


 About Us   |  Advertise on DiscoverCircuits.com   |   Report Broken Links  |    Link to DiscoverCircuits.com  |    Privacy Policy


Copyright  January, 1998 - November, 2017     David A. Johnson & Associates.  All Rights reserved. 


 Linking is ALLOWED but COPYING any content or graphics to your web site is EXPRESSLY PROHIBITED.