This is a homework exercise?
It should be in the homework subforum.
no, this is my project for school
What is the circuit supposed to do?
Seems a bit odd. If you connect the battery when there is no light on the LDR, the thyristor will turn on, the LED will start glowing and there will be a click in the speaker. When the LDR gets illuminated - it depends on the thyristor and the speaker (a thyristor will not turn off if the load current is large enough).
this is the circuit of a laser security system
Can you explain in more detail?
From http://en.wikipedia.org/wiki/Thyristor :
Thyristors have three states:
Reverse blocking mode — Voltage is applied in the direction that would be blocked by a diode
Forward blocking mode — Voltage is applied in the direction that would cause a diode to conduct, but the thyristor has not been triggered into conduction
Forward conducting mode — The thyristor has been triggered into conduction and will remain conducting until the forward current drops below a threshold value known as the "holding current"
Another thing I would like to add is the thyristor is BT-169
What can you tell us about the Speaker?
Have you bought the components? How does the laser get used?
Look at http://www.nxp.com/documents/data_sheet/BT169_SER.pdf [Broken]
A slight problem: BT-169 is not specified for DC operation.
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