Thursday, August 30, 2012

Toothbrush Timer

toothbrush timer in action

Putting young kids to bed is a lot like wrangling cats; lots of running, chasing, screaming, and occasional scratching.  So come bed time, oral hygiene for my girls usually consists of sticking the toothbrush in their mouths, wiggling it around for a few seconds, then fighting over who gets which stool to reach the sink.  The dentist told them they need to brush for one minute.  As time tends to be a bit abstract for young kids, I figured an electronic timer might help improve their brushing habits.  Given the recent passing of Hans Camenzind, the inventor of the 555 timer chip, I thought it appropriate to make a circuit with that chip in his honor.

timer circuit diagram

A quick search on Google turned up this simple adjustable timer circuit utilizing the 555 timer.  When you turn the timer on, a green led lights up.  After the preset time elapses, the green led goes off, the red led lights and a buzzer sounds until the power is turned off.  The time is adjusted with the potentiometer.  Just what I was looking for.  It looked easy to build and I had most of the parts on hand so it wouldn't cost much.

stripboard layout

I have always wanted to build something into an Altoids tin.  This seemed like the perfect opportunity.  I apologize for the lack of build photos but I usually use my cell phone camera, and my cell phone is on the fritz.  The circuit diagram and the stripboard layout are pretty self explanatory however.  Just keep in mind on stripboard, all of the holes are electrically connected horizontally.  So if you are using standard PC board or perfboard, you will have to make the horizontal connections yourself.  For example, the upper end of the 100K resistor and the lower wire of the potentiometer are electrically connected, even though it is not evident on the stripboard diagram.

inside view

Surprisingly, I couldn't find any large green led's in my collection of parts so I substituted a blue one.  Despite the messy appearance, the circuit worked first time.  After a few attempts with a stopwatch I had the potentiometer dialed in for one minute.  I'm not too happy with the Altoids tin though.  The potentiometer is too large to fit, so I had to cut a hole in the top of the tin.  I wanted it hidden so no one would change the time setting.  I'll probably swap out a micro potentiometer in the future.  And, I still need to find or make a knob to fit the power switch.  But it works, and the kids get excited about using the timer when brushing their teeth.  Don't miss the captivating video demonstrating the timer in action.

No comments:

Post a Comment