Please help me understand this circuit schematics (Door Alarm)

How do the bare wire loop (door knob), Q1 and L1 form a high-frequency oscillator ?
What are the purposes of C1 and C2 ?

I cannot simulate correctly the bare wire loop. How do I simulate this circuit correctly ? Which open-source simulation software to use ?

What happen to Q2 and Q3 when I touch and NOT touch the bare wire loop ?

Can someone elaborate it in MORE DETAILS ?

I'm not sure why this oscillates, but it says right on the schematic that L1 is 10uH.

kevin998x said:

How do the bare wire loop (door knob), Q1 and L1 form a high-frequency oscillator ?

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where does it say that Q1 & L1 form a high frequency oscillator ?

What are the purposes of C1 and C2 ?

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these are standard bypass caps placed across bias resistors so that the bjt can operate at some frequency at its bias point.

I cannot simulate correctly the bare wire loop. How do I simulate this circuit correctly ? Which open-source simulation software to use ?

Click to expand...

falsted is decent for simple analysis. I see you already have that, though your circuit is incorrect. Whats the 1F cap for ?!? And similar differences.
A wire loop should be modeled as an inductance i think. Touching the knob will change this inductance. Note that the pot has to be adjusted so that the circuit is just on the threshold of triggering.

What happen to Q2 and Q3 when I touch and NOT touch the bare wire loop ?

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presumably they turn on or off, hence lighting the LED and triggering the Nand gate oscillators to produce a siren/ alarm sound.

Can someone elaborate it in MORE DETAILS ?

Click to expand...

hope this sets a direction for your further analysis ?