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Return to BlogDummy Alarm with Flashing LED
Posted Jan 14, 2012 at 12:01 pm
Figure 1
A LED flashing briefly once every 5 seconds to imitate the indicator of a real alarm is the function of this dummy alarm project with the use of a 7555 timer IC.
To prolong battery life, the circuit was designed to use very little current in order to be left ON permanently. Optionally, an ON/OFF switch may be included if desired. The circuit uses a low power version of the standard 555 timer, the 7555 timer IC. A bright flash with a low current is provided by a super bright red LED. The average total current for the circuit is less than 0.2mA since the LED is OFF for most of the time. A set of 3 alkaline AA cells should last for several months or a year with this very low current.
A standard 555 timer IC can also be used in the circuit which will increase the average current to about 2mA while the battery life will be much shorter. If a greater power supply voltage at 15V maximum is used in this alarm, the 1K resistor for the LED should be increased to keep the LED current low around 3mA.
Click here to see the rest of the project.
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2 years ago: the project is simple and good
1 year ago: really its an good intiative to the beginners
1 year ago: What is the function of each components?
3 weeks ago: Thank you so much for diagramming these alarms out. I have just started to get into all of the circuitry involved and have been looking for some easy projects to cut my teeth on. Thank you so much for the great project idea.