Can anyone explain me this circuit

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SUMMARY

The discussion centers on a laser security system circuit utilizing a BT-169 thyristor. When the circuit is powered without light on the Light Dependent Resistor (LDR), the thyristor activates, illuminating an LED and producing sound from a speaker. The circuit's functionality is contingent on the thyristor's ability to maintain conduction until the load current falls below the holding current threshold. Additionally, it is noted that the BT-169 thyristor is not recommended for DC operation, which may pose challenges in practical applications.

PREREQUISITES
  • Understanding of thyristor operation, specifically BT-169 characteristics
  • Familiarity with Light Dependent Resistors (LDR) and their behavior in circuits
  • Knowledge of basic electronic components, including LEDs and speakers
  • Awareness of circuit design principles for security systems
NEXT STEPS
  • Research the operational characteristics of the BT-169 thyristor in AC vs. DC applications
  • Explore alternative thyristors suitable for DC operation in security systems
  • Learn about designing circuits with LDRs for light-sensitive applications
  • Investigate the integration of sound output devices in electronic security systems
USEFUL FOR

Electronics students, hobbyists working on security projects, and engineers designing light-sensitive circuits will benefit from this discussion.

gaurav_dua
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http://prntscr.com/60xcwx

Thank you
circuit.jpg
 
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This is a homework exercise?

It should be in the homework subforum.
 
NascentOxygen said:
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).
 
NascentOxygen said:
What is the circuit supposed to do?
this is the circuit of a laser security system
 
Svein said:
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).
Can you explain in more detail?
Thanks
 
gaurav_dua said:
Can you explain in more detail?
Thanks

From http://en.wikipedia.org/wiki/Thyristor :
Thyristors have three states:

  1. Reverse blocking mode — Voltage is applied in the direction that would be blocked by a diode
  2. 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
  3. 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"
 
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Another thing I would like to add is the thyristor is BT-169
 
  • #10
What can you tell us about the Speaker?

Have you bought the components? How does the laser get used?
 
  • #11
gaurav_dua said:
Another thing I would like to add is the thyristor is BT-169

Look at http://www.nxp.com/documents/data_sheet/BT169_SER.pdf

A slight problem: BT-169 is not specified for DC operation.
 
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