# How to choose a Buzzer for a wall current detector, when buying?

#### Aleksandari-

Joined Mar 6, 2021
3
Hi.

In this scheme
,

as they should be parameters for Buzzer?

For mentioned scheme, how to choose the right Buzzer, when buying?

With what range of current and voltage (nominal, operating voltage, ...)

#### KeepItSimpleStupid

Joined Mar 4, 2014
4,556
I ~= (9-2.1-0.6)/220 is about 28 mA
5-6 V

Joined Jan 15, 2015
5,876
Well to start with the 2N3904 NPN Transistor has a maximum forward current of about 200 mA if I recall correctly. Given a choice I would place my buzzer in parallel with the LED and LED current limiting resistor. Battery voltage is 9 volts and unfortunately they do not give any information about the buzzer used. They also do not mention the Vf (forward voltage) drop of the LED. This leaves a lot of guesswork. A typical Red Led will have a forward voltage of about 1.2 volts and a forward current Max of 25 mA. So running it at 20 mA I get 9volts - 1.2 volts = 7.8 volts / 0.020 amp = 390 Ohms. So use a 390 ohm resistor in series with the LED. I would then just parallel a 9 volt buzzer with the LED and series resistor. Buzzers are pretty forgiving and normally have a voltage range like 6 to 9 volts or 3 to 6 volts. Just find a low current buzzer in a 6 to 9 volt range. The LED current will be 20 mA of what you have available on the 2N3904 transistor. Most small buzzers are 20 to 50 mA.

Ron

Joined Jan 15, 2015
5,876
I ~= (9-2.1-0.6)/220 is about 28 mA
5-6 V
Well we hit that at the same time. Pretty forgiving circuit. I have seen that and similar but have no idea how well they work.

Ron

#### Aleksandari-

Joined Mar 6, 2021
3
The problem is that they only provided data for resistors and transistors, while for Buzzer and switch they only showed on that diagram (picture) that it is needed and they did not specify anything more, no necessary properties. There are a lot of different types of Buzzer and switch on the market and they didn’t specify which one fits that particular diagram.

#### Aleksandari-

Joined Mar 6, 2021
3
and normally have a voltage range like 6 to 9 volts or 3 to 6 volts.
No, in the stores where I buy Buzzers, there are also 12V, 20V, 1.5V, ...

Joined Jan 15, 2015
5,876
Most 12 volt buzzers will do just fine on 9 volts. A simple Google of AC Voltage Detector will bring up about a dozen variations of the circuit you posted. Some may give a part number for a buzzer. Things like common buzzers are readily available. Just make sure the voltage and current comply with your driver transistor. This is all pretty generic. You could use a 12 volt battery and a 12 volt buzzer. The 9 volt battery is there simply because they are abundant and convenient. Again, I would configure my buzzer and LED as shown below:

Note how the LED and buzzer are in parallel. Note how the buzzer is just a generic 6 to 12 volt buzzer.

Ron