HELP: Automatic bell using microcontroller

Replies

• 

  reachrkata

  Here goes -
  
  Refer the datasheet of DS12887 on the internet. Its a Real Time Clock IC. The Controller AT89C52 is reading the clock data and displaying it on the LCD.
  In addition, at required time conditions (Eg . Every one hour) based on the RTC value, it also activates a relay which turns on a Bell.
  
  L7805 is the Power supply for the controller, RTC and Relay coil.
  
  There is however one major mistake in the circuit. The emitter of Q2 needs to be connect to GND. 😒
  
  -Karthik
  
• 

  rohit330

  Thanks @ reachrkata
  by the way, could you just explain how those two transistors used to drive the relay... I think, interrupt is providing at the time we require output on our buzzer.. right? so, a low is fed to npn...
  and then, R4 to R11 are pull up resistors?? for ?? 😐
  then a pot on 9th pin of lcd..then C6, R15 on 8952 RST pin 😔
• 

  reachrkata

  To answer your questions -
  
  1) Its the other way, when we require to activate the buzzer, a HIGH is given by the port. This drives Q2 to saturation, which inturn drives Q1 to saturation and 12V is applied to the relay coil which then activates the relay. The Q1-Q2 circuit is added because the microcontroller cannot by itself drive the 12V relay coil.
  
  2) I am exactly not sure why the R4-R11 pull-ups are present. Perhaps you can check the datasheets of the controller and RTC to get an idea.
  
  3) The Pot perhaps does the job of providing the LCD bias voltages. LCD biasing is a separate topic in itself and you can google it for more info.
  
  4) The RC in the Reset pin is usually added so that transient spikes on the reset line do not unnecessarily reset the controller.
  
  -Karthik
  😁
• 

  reachrkata

  To answer your questions -
  
  1) Its the other way, when we require to activate the buzzer, a HIGH is given by the port. This drives Q2 to saturation, which inturn drives Q1 to saturation and 12V is applied to the relay coil which then activates the relay. The Q1-Q2 circuit is added because the microcontroller cannot by itself drive the 12V relay coil.
  
  2) I am exactly not sure why the R4-R11 pull-ups are present. Perhaps you can check the datasheets of the controller and RTC to get an idea.
  
  3) The Pot perhaps does the job of providing the LCD bias voltages. LCD biasing is a separate topic in itself and you can google it for more info.
  
  4) The RC in the Reset pin is usually added so that transient spikes on the reset line do not unnecessarily reset the controller.
  
  -Karthik
  😁
• 

  rohit330

  Thanx @ reachrkata 😀
  For microcontroller, no internal pull ups are there for port 0. And that pot is for contrast setting of lcd. Then RC circuit to reset the MC every time it starts.. I asked one of his friend.. Just wanted to know more..
  Regards..😀