I need to design a circuit that has three LEDs, each LED has its own push button switch, but there is only one common buzzer.

Goal: when a push button is pressed its corresponding LED should glow along with the buzzer sound.

  1. Design the circuit with single battery source.
  2. Design the circuit with two battery sources such that when a push button is pressed LED should glow from one battery source and buzzer should sound from other battery source.

Please help me with either of the above two circuit diagrams.

  • 2
    \$\begingroup\$ Welcome to EE.SE. Your question seems to be something like a homework. But you should show your effort first before requesting help. What have you tried so far? You can either draw schematic via the extension or upload a photo of well-drawn schematic. \$\endgroup\$ Feb 20, 2019 at 5:25

1 Answer 1


This is simply 3V batteries with LED and Current limiting switch with Diode OR logic. and a 3V Piezo Buzzer .


simulate this circuit – Schematic created using CircuitLab

  • If White LEDs then no 50R resistor needed, if 3V battery max. If Red or Yellow 2~2.1V , 0.9V drop/50~18mA
  • \$\begingroup\$ This circuit is above my child standard, he is just in 8th class and need the working model for the exhibition, we followed your procedure without R1, R2, R3, R4 and 1N4148 but all LED glows by pressing any of the switch but if we dont use buzzer it works fine. Does R4 and 1N4148 part is compulsory? what is 1N4148 ? or what else we can use in place of 1N4148 that can be easily available ? \$\endgroup\$ Feb 20, 2019 at 8:12
  • \$\begingroup\$ USe any diodes, make sure they aren't in backwards and R4 prevents Q1 from damage Diodes isolate each LED from the each switch. DIODE OR logic \$\endgroup\$ Feb 20, 2019 at 9:56

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