[SOLVED] buzzer problems & 8051

[punisherzz]

hello all,

i have implemented the given circuit , in hardware and software, the 8051 code is simple i give a pulse of 0.5s at pin 2.0. Neither the hardware nor the software is working :???: :sad:, i have attached the Proteus design. please tell me why buzzer does not give a beep whereas the LED does, is the current low or what.
and recommend a possible solution.

regards.

PS: there is no problem with the buzzer, i checked by connecting it to the Vcc of my real cct , it works at 38mA , my transistor Beta is 130. Ib=25uA. Ic=2.2mA. Ie=2.16mA (real circuit).

 

[amol_shah]

Put a pull up resistor at transistor base. Check this link: Interfacing Relay to Microcontroller | 8051 Tutorial | Tutorial
Instead of relay Put a buzzer over there and check if the buzzer works at 5v or at 12v.

 

[vlsi_whiz]

I think the problem is with the Reset, you cannot always connect the reset to ground via pull-down. You need to put in a reset switch. Since the uC has its reset pin low when power-up, it will not be in a good known state and so it will not function properly. After power-up, you need to apply reset by driving the reset pin high for some time and then de-assert it by driving it low. This will put all the memories, statemachines, and logic in the uC to the IDLE state and the uC will start up correctly.

I suggest you try reseting the uC after you power-up the ckt and then check if it works.

 

[prakashvenugopal]

Hi,

Just increase the reset period by changing the capacitor 10uf instead of Capacitor 1uf. This may work. To be safe, i will design my power on reset circuitry for 500ms.

 

[punisherzz]

@vlsi_whiz and prakashvannugopal, i forgot to change the reset circuitry in the proteus design, im sorry abt it, but when i implemented the hardware, i placed same (exact) circuit with momentary switch and 10uF capacitor as given in mazidi book and it works fine in hardware, i have tested it. so the problem doesnt lie in reset circuitry, there is some problem with the BJT design.
PS: also changed the uC, but no help.

---------- Post added at 14:05 ---------- Previous post was at 14:05 ----------

thanks for the guide, ill try it.

---------- Post added at 15:56 ---------- Previous post was at 14:05 ----------

just needed the pullup resister of 4.7k from Vcc to supply enough current to base, so that BJT goes in saturation thus providing the current to the buzzer. thanks all.