Cheap Continuity tester?

Thread Starter

musicalavtech

Joined Mar 23, 2012
54
What values of resister and led would work in series with a cheap tone generator, and a 9V? Only needed to check unpowered wiring circuits for shorts.
 

dl324

Joined Mar 30, 2015
14,468
What values of resister and led would work in series with a cheap tone generator, and a 9V?
Many DVM's have an audible continuity checker.

The continuity checker I use most uses 2 AA batteries and a flashlight bulb. An added benefit is that it can check diode junctions and most LEDs. The last time I bought one they were a couple dollars.
 

Thread Starter

musicalavtech

Joined Mar 23, 2012
54
It's just for point-to-point wiring on a panel that is unpowered. To quickly check for shorts before powering up. I have a meter to use after powering up, to check voltages. I know 2 leads, battery, and buzzer is the super simplest, but I thought to add a led for noisier environments. I don't even need a switch.

#12 mentioned a 1k resistor, as long as a buzzer or other cheap audible would work.

Because the panels are good size, with no good place to set a meter, is why I want to use this.
 
Last edited:

RichardO

Joined May 4, 2013
2,271
I have 2 continuity testers.

The simple one is an old Sonalert with a 9-volt battery. Shorting the leads powers it up. This is fine for cables that are not connected to anything. It also is a quick way to test LED's. I never use it in a circuit because of its high voltage and current.

The other continuity tester is more specialized. Since its open circuit voltage is less than a diode drop, it can safely be used in IC and transistor circuits. It only beeps if the resistance is less than about 100 ohms. This beeper is used to verify correct wiring of prototype circuits or to follow traces on a PCB.
 

MisterBill2

Joined Jan 23, 2018
11,892
A sonalert can work very well, but not that cheap. Most continuity beepers use a one or two transistor oscillator and a speaker. But a 4049 hex inverter can use one section as an RC oscillator and the other five sections as an amplifier to drive a speaker quite loud. All those parts should add up to not much. The speaker and battery will be the expensive items.
 

AnalogKid

Joined Aug 1, 2013
10,057
A small piezo beeper (not the bare piezo element) should be able to act as the current limiter for the LED. $2.24, Digj-Key

Battery + > LED > Beeper > Battery -

Break the loop anywhere to insert the test leads.

ak
 
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