jeffrey said:
I am a high school student and need this for a science fair experiment.
I want to be able to record exactly how long it will take for the
person to wake up. As soon as the buzzer wakes them up, they will
press the button to stop the stopwatch.
So at a predetermined time at night (say, 5AM, or 2AM, or whatever),
the buzzer will go off and a stopwatch will start counting up. As soon
as the person wakes up, they will press a button to stop the
counting-up. They will record whatever the stopwatch says on a sheet
of paper. (Or, if possible, the time will be stored onto a memory
chip.)
I need to make this device as dummy-proof as possible, so many students
will participate in my experiment. It needs to be as cheap as possible
to build and it needs to be very easy to use (All they have to do is
press a button and the time shows up. They don't need to set anything,
or do anything whatsoever.)
Ok - I can give you part of it. First, break it down into
3 pieces:
------- --------- ---------
| Alarm | | Control | | Elapsed |
| |========>| |======>| |
| Clock | | Logic | | Timer |
------- --------- ---------
The alarm clock is a battery powered (*important* for safety)
travel alarm clock you can buy. You can also buy the elapsed
timer. See the web sites below for possible examples.
http://www.seniorshops.com/multitimer.html
http://fantes.com/timers.htm
The control logic input is as follows:
+Vcc ---------------+--------+
| |k
[Relay] [1N4001]
| |
+--------+
Alarm |
Clock /c
Piezo + ---[1K]----| NPN 2N3904
Buzzer \e
|
Ground
When the alarm rings, the relay will energize;
when the alarm is turned off by the subject, the
relay will de-energize. Ground connects to the
negative side of the supply and the negative
side of the battery in the clock.
If you use a clock/timer/stopwatch other than what
I describe below (for example, one of those on the
links I furnished above), then additional circuitry
will be needed, and cannot be specified without
knowing details about the device you choose.
If you use another battery powered travel clock like
the ones at the Electronic Goldmine link I posted,
then you can connect the relay operating point and
normally open point to the double sided PC board
I mentioned in an earlier post, ans slide that
into the battery compartment of the elapsed time
clock, between the battery + post and the contact
in the battery compartment of the clock. That second
clock will start running when the alarm rings, and stop
running when the subject turns the alarm off.
You *will* need to ensure that the alarm is set before
each test. Whether you let the total time accumulate
on the elapsed timer, or record it each time (and
reset the elapsed timer if you like) is up to how you
want to perform the experiment.
The above approach is about the cheapest/easiest you can
use for your experiment. You can go for a more high-tech
looking project at increased cost/complexity. You can also
go for a higher precision in counting the elapsed time, again
at a higher cost/complexity. You'll need to consider your
budget/skill/time available to decide which way to go.
Ed