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.

 

A cheap mutlimeter is cheaper/better than all the components you got there.

http://www.ebay.com/itm/Digital-LCD...158808?hash=item4196e05658:g:v2oAAOSwPYZU~-Bg

 

9 volts, 1K, and an LED...in series.

 

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.

Do you need the tone generator? Couldn't the LED serve as your indicator?

Are you testing points that could be damaged by 9V?

 

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.

 

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.

 

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

Adding an LED in parallel with the buzzer will not stop the buzzer.

 

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.

 

I ended up re purposing an old dog collar beeper. 6V battery, beeper...I soldered long "leads" to it, and it works as intended.

 

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.

 

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