DIY Dirt Cheap Continuity Tester with LED + 555 IC

Picture of DIY Dirt Cheap Continuity Tester with LED + 555 IC
Hi, i wanted to have a continuity tester (my multimeter doesn't have a buzzer) so i don´t have to look away from the circuit I am testing to see the multimeters display. Although i wanted a buzzer i also added a LED and an on/off switch for late night tinkering "stealth mode"
I don´t have any engineering or electronics background (actually i am a surgeon), but i love to make stuff and i am self teaching electronics with the help from Google and . This is my first instructable and English isn´t my native tongue, so bear with me please...

DISCLAIMER: If following this guide anything/anyone/yourself damages i shall not be held responsible.Do it at your own risk. Take all the safety measures (goggles, gloves, etc)
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Step 1: Bill of materials:

-Highlighter (worn out)
-Blue LED
-555 IC
-0.01uF ceramic capacitors= 2
-1uF electrolitic capacitor = 1
-180 k resistor = 1
-56 k resistor= 1 (i did it on the weekend with no opened stores, so i used 47k + 10k series resistors)
-Piezo buzzer= 1 (i used a Hycom HY-07 that i took from an old modem)
-Button cell batteries= 3
-Battery holder (from a cheap-o pen/flashlight i had)

-Soldering Iron
-hot glue gun
-xacto knife

Step 2: Let the stripping begin..

Picture of Let the stripping begin..
First of all, i took apart the highlighter, threw away the tip and the ink cartridge by cutting the back end with an xacto knife. And i did the same to the flashlight/pen in order to take the battery holder away.

Step 3: Test 1,2,3

Picture of Test 1,2,3
I found a buzzer circuit ( ) the easiest and simple circuit i could find and tried it on the breadboard. It worked out fine, except i changed de 10k resistor (pins 7 and 8 of the 555 IC) for a 180k resistor because i liked the tone better.

Step 4: Avengers Assemble

Picture of Avengers Assemble
i soldered all together over the 555 directly trying to make it as compact as possible (although i had plenty of room inside the highlighter, i did that way just in case i want to house it in a smaller pen someday)
Phil B1 year ago
You are brave to solder directly to the IC. I tend to destroy ICs and try to use a socket to avoid static electricity damage. The US Navy Electronics course is available free for download (1998 edition) here. It is a great resource for anyone who wants to learn basic electronics from beginning to end. Thank you for your very practical Instructable.

me shahbaz from lahore student of laptop repairing also basic electronic ,plz add me

in ur friend my email is

skype id . shahbaz007761

thegrendel1 year ago
If you use a piezo buzzer module, rather than a piezo speaker,
then you can omit the 555 and associated components. A piezo
buzzer needs only current applied to buzz, and requires no oscillator
to drive it.

Nicely done project, though.
lean04 (author)  thegrendel1 year ago
thanks, i´ll have that in mind for next time.
lean04 (author) 1 year ago
Thanks, the 555 timer is like the swiss army knife of electronics, and internet is a great powerful tool for courious people like us..
jaesn1 year ago
Great Idea! Got to love the versatility of the 555 timer. Also, how great is the internet? I'm teaching myself electronics through the same method.