I will try to describe about my problem again as much as possible, please let me know if there is any information is left out because it's getting a little confusing :


1. I want configure the MCU to switch 'ON' a very loud alarm buzzer whenever a certain requirement is met.

2. However, conventional buzzer on market normally have very low output volume so, instead of buying a conventional buzzer, i bought a very cheap battery (1.5vx3) operated magnetic switch sensor with alarm built-in (those sensor u attach at the door to detect any attempt to open the door). I decided to use the built-in alarm since it has ear-piercing output which is perfect for my project.


Built-in Alarm Circuit description
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Note : From now onwards, whenever i mention the word buzzer, it actually refer to the whole built-in alarm circuitry. I am not sure what exactly components are there on the circuit since it's quite small. It has a customized IC that i know nothing of (something like a black lump of clay if anyone knows what i mean). It also has an built in (i think)feedback oscillator circuit since it has a RC tank, and one high rating capacitor (i am not sure if this is a capacitor since it has 3 legs but it's twice as big as common capacitor). One of the 'capacitor' leg (middle) is connected to the ground. The other 2 legs (left and right) is connected directly to a piezo diaphgram and i believe these 2 legs carries high voltage since i get electrocuted when touching them. And finally, a switching transistor and a magnetic sensor (that goes 'short' if a magnet is presence nearby and 'open' if the magnet is taken away) which i think is not relevant to the alarm circuit since i have the alarm circuit ON at all time and will sound once power supply is connected.


3. I tried connecting the power supply to +5V Vcc directly instead of the 4.5V battery and it works out perfectly. Problems starts to kick in when i try to interface it to the MCU. Also, it's good to note that the only access i have now is the +ve and -ve terminal of the buzzer circuit since i do not dare to interfere with the remaining circuits in between because it's kind of complex.

I am using P1.0 of the MCU as signalling pin.

First Method :

I connected +5V Vcc directly to the +ve terminal of the buzzer and GND to the -ve terminal of buzzer, trying to use current sinking method by turning the alarm on by setting P1.0 to 'low' logic. Obviously, it is not as simple as that and it doesnt works (no sound at all). So i scrap off the idea.

Second Method :

I am using a PNP Transistor(JA101Q). Firstly, i connect the 'B' to the P1.0 through a 10k resistor. After that, i connect 'E' to the +5V Vcc. The 'C' is connected to the -ve terminal of the buzzer. The +ve terminal of the buzzer is tied to GND.

Problem : When i give a 'low' logic signal to P1.0, the circuit works but it only output a very low hissing sound. This is what i am trying to figure out at the moment and i need helps.


Any idea what would be the most efficient way to switch on/off this alarm?