i tried to simulate the circuit below with the Proteus 8 Professional , but i didn't find the SL100 transistor so i replaced it with BC547 , is it ok? and when i give the pin 4 high , the LED starts to pulsing but the buzzer doesn't work .

can anyone help me to simulate this circuit ? enter image description here

  • \$\begingroup\$ What happens if you change R4 to 100 ohms? But I'd move LED1 and R5 to across the speaker. \$\endgroup\$ – PeterJ Apr 26 '16 at 12:07
  • \$\begingroup\$ Can you explain more ? \$\endgroup\$ – Abdu Jellah Apr 26 '16 at 13:09

The transistor is being used as a switch so you should be able to use almost anything provided it can handle the current - not that a 1/2W speaker needs much current. As for the lack of sound, are you using a speaker or a buzzer, if your using a speaker, the frequency driving it may be too low, if you can see the led pulsing, it's got to be below 50Hz, not many small speakers work well at those frequencies. Try fiddling with VR1 to see if you can the circuit to buzz at an audible frequency.

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  • \$\begingroup\$ I tried both buzzer and a speaker, there is no sound at all . \$\endgroup\$ – Abdu Jellah Apr 26 '16 at 11:36

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