I have been trying to use a TMB12A03 buzzer in a circuit. It doesn't sound when I think it should. I finally constructed a simple test circuit to try to understand what's going on. When I put a 9V battery across the terminals of the buzzer, it sounds. When I put the 9V battery across the buzzer in series with a 1K resistor, it doesn't sound. (see attached sketch).

What am I missing? The buzzer has the positive terminal marked, and I was careful to make sure to observe the polarity when connecting it to the battery. I measured the resistance across the terminals of the buzzer, and it is in the 1M range--so I wouldn't think adding a 1K resistor in series would make much difference. I also tried several different buzzers from the same batch with the same result, so I know it isn't a failed buzzer.

I downloaded the data sheet but didn't see anything that would indicate why it isn't working. (see attached file).

I'd appreciate any insight or suggestions.

 

Your resistance reading is leading you down the garden path.

Take the maximum voltage and the maximum current and apply Ohm's law, this will give you a better idea of the resistance while operating.

 

Measuring the resistance of the buzzer is meaningless because it is not a resistor.

 

I'd appreciate any insight or suggestions.

I have some of those beepers and a 150 ohm series resistor works fine at 9 volts

 

 

The datasheet for the buzzer says, "rated voltage= 3VDC, operational voltage= 1.5-5VDC" NOT 9VDC. Current= 30mA Max at 3V rated voltage.
A series1k resistor with 30mA in it has a voltage drop of 30V then of course the buzzer does not work.

 

So to operate the buzzer from a 9V battery, you should use a (9V-6V) / 30mA = 200Ω nominal resistor in series.

 

It seems to me, those buzzers are designed to be fed from a voltage source . Add a resistor in series as suggested, and add a 100 uF 10V capacitor across to pins of the buzzer for reliability

 

Thanks for the helpful advice and suggestions.

I substituted a 150 ohm resistor for the 1K and now the buzzer works. Out of curiosity I measured the voltage across the buzzer and the current through the buzzer with the 150 ohm resistor in series; the voltage was 5.32V and the current was 26 mA, giving an effective resistance of about 200 ohms for the buzzer in that configuration.

 

Stop thinking about resistance for things that are not resistors. It is only misleading.

 

Stop thinking about resistance for things that are not resistors. It is only misleading.

I understand what you're getting at, but then why do we talk in terms of "input impedance" and "output impedance?" In Horowitz and Hill they talk about the output and input impedance of an emitter follower. So when is it valid to talk about the resistance or impedance of a circuit or component and when not?