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The circuit is a motion detection alarm circuit, I know what the circuit does but I want to know about the resistors attached (R2 is attached to the transistor for amplifying the output to 5V). Why R1 and R2 are attached? Anything do with the delay? Can you explain to me the relay circuit of npn transistors?

PIR circuit

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  • \$\begingroup\$ To limit the current to the LEDS to keep them in spec and not burn them out. \$\endgroup\$
    – Trevor_G
    Commented May 26, 2017 at 14:58
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    \$\begingroup\$ Yuk. It hurts to look at that fuzzy image. \$\endgroup\$
    – Olin Lathrop
    Commented May 26, 2017 at 16:35
  • \$\begingroup\$ by removing R1 and led can i replace it with a DC motor? if so then what voltage DC motor should i use? \$\endgroup\$
    – Santosh Divakaran
    Commented Aug 26, 2017 at 13:40

1 Answer 1

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R1 protects led 1 from dying.

R2 protects q1 from dying. It also sets the base current that is multiplied by the gain of the transistor to allow that much current through the C-E junction.

Diodes like led 1 and the base of a transistor must be current limited so they don't go into a overload condition and burn out.

The delay is completely internal to the PIR module.

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  • \$\begingroup\$ so that is 5v through the C-E junction in this cause ,any way of increasing the output voltage to 8v ??? \$\endgroup\$
    – Santosh Divakaran
    Commented May 26, 2017 at 15:06
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    \$\begingroup\$ Yes, by replacing the 5V of the circuit with 8V. Then you have to change the resistors too so that the leds don't break. And if the PIR module or buzzer don't work with 8V. Change them too. Or you could disconnect the 5V from led2/the buzzer and connect just that to 8V. The transistor does not amplify or double the voltage. It acts like a switch. \$\endgroup\$
    – Passerby
    Commented May 26, 2017 at 15:18
  • \$\begingroup\$ by removing R1 and led can i replace it with a DC motor? if so then what voltage DC motor should i use? \$\endgroup\$
    – Santosh Divakaran
    Commented Aug 26, 2017 at 13:35

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