project not working

Thread Starter

Chief400

Joined Mar 17, 2015
9
I recently found this web site which showed how to build the "ultimate continuity tester." The link is here http://electronicdesign.com/analog/ultimate-continuity-tester-hides-many-tricks-its-sleeve
I built the tester and followed the schematic very carefully on a bread board and have rechecked several times. The tester has a buzzer attached, but it will not buzz when the probes are contacted, the buzzer will only make one chirp per contact. I'm assuming the problem is with one of the transistors or the resistors feeding the transistor. I would appreciate any ideals as to what the problem might be. Here is a link to the schematic http://electronicdesign.com/site-files/electronicdesign.com/files/archive/electronicdesign.com/files/29/19768/fig_01.gif
Thanks
 

wayneh

Joined Sep 9, 2010
16,237
You probably have the wrong type of buzzer, one that requires a buzz signal, instead of one that needs only power to buzz. Shoot us a photo.

Oops, I read the description and see that the circuit itself is meant to drive the buzz. I guess the photo is even more important to help you diagnose the problem.

Do you have a multimeter so you can measure voltages at various points?
 

wayneh

Joined Sep 9, 2010
16,237
Hmmm...Well one thing you could do is neaten things up a lot by using your power rails more effectively. Don't build your own "rail" on the breadboard and run jumpers - use those side rails.

It's easy to have intermittent connections in this type of build and especially when the components have differing lead diameters. You can use a meter to verify that the leads of a component are actually in contact with the board.
 

Thread Starter

Chief400

Joined Mar 17, 2015
9
Thanks wayneh for your reply. To show my ignorance, are you saying like when resistor, capacitor, etc. goes to the positive, to actually attach it in the power rail?
 

wayneh

Joined Sep 9, 2010
16,237
That looks better. Question: How certain are you of those resistors? I've never seen the red ones like those. I'm just wondering if there is any chance they are inductors, or whether you may have misread the color codes.
 

DickCappels

Joined Aug 21, 2008
6,185
To Wayneth's point, it looks like the wrong kind of buzzer to me.

The schematic indicates a piezoelectric transducer or speaker/ Most of the encased transducers that I have seen and used look like the one shown in the photograph below and produce sound when driven with an audio signal, such as pulses from an oscillator.

The cylindrical ones, in my experience have circuitry inside and produce a tone when DC is applied.

If you apply 1.5 to 3 volts to your buzzer and a tone comes out, then you have the wrong part, as Wayneth first suggested.
 

Thread Starter

Chief400

Joined Mar 17, 2015
9
Thank you guys. I ordered all the parts from Mouser, so I'm pretty sure the resistors are correct. The speaker is one I had and I thought it was a piezo. I will go get one as suggested and try that. Will let you know.
 
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