Home > Circuit Blox > Remote Panic Alarm
REMOTE PANIC ALARM
UPDATED:.12:18 29 June 2014
OPERATION NOTES

This circuit will activate or deactivate a siren by pressing the appropriate button on a handheld infra-red transmitter:

  • #1 = Turn siren Off
  • #2 = Turn siren On

It is advised to use a paper or mylar cone speaker of at least 1W. Do not use high quality speakers for home entertainment systems.

Circuit Voltage: 6 to 12 volts

Infra-Red Transmitter/Receiver
Select the required channels using the jumper

Link A0 = Ch1,2
Link A1 = Ch3,4
No link = Ch5,6.

TRIANGLE WAVE ASTABLE:
Adjust the warble rate using VR1. Start with VR1 set at minimum, fully anti-clockwise.

ASTABLE:
Set Range 2 or 3 for audio frequencies. Adjust pitch using VR1


BLOCK DIAGRAM
CIRCUIT BLOX

EXPLANATION

The transmitter sends a coded pulse using Infra-Red light. A different code is sent for each button and channel.

The receiver picks up the coded signal.

  • If it is the correct signal for #2, it sends #2 output high which connects to the "Set" input on the Latch. The output of the Latch is sent high which connects to the -"Reset" on the Astable. This enables the Astable to oscillate its output which connects to the Darlington Driver and Speaker producing a loud siren sound. This will continue even when the button on the Transmitter is released because the Latch holds its state.
  • If it is the correct signal for #1, it sends #1 output high which connects to the "Reset" input on the Latch. The output of the Latch is sent low which disables the Astable and ceases sound production.


TEACHING OPPORTUNITIES: DEVELOPMENT:
Topics could include:
  • Infra-Red communication:
  • Data Transmission
  • Domestic remote controllers
  • Home Security control systems
  • Safety in the home for the elderly
  • Frequency Modulation
  • Sound Generation.
To increase the sound level at high frequency, a 10W or more bullet tweeter can produce some very loud sound with a 12v supply or more.

Beware - it is very loud!

The siren generation section could be removed leaving just the Infra-Red and the Latch. The output of the Latch could connect to a Relay with Driver, or a Darlington Driver, to control a different device offering remote on/off operation.


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