DIY Laser Trip Wire Alarm -- The Learning Circuit 84

DIY Laser Trip Wire Alarm

The Learning Circuit | element14 presents | Project Videos

Now that we know how laser diodes work, it’s time to use one in a project! Karen uses a laser diode and an LDR sensor to create a “trip wire”. When the “wire” is “tripped”, meaning the laser beam is interrupted, lights will flash and an alarm will sound! To create the alarm siren, Karen couples together two 555 timer circuits. The entire project is triggered using a third 555 timer circuit used in bistable mode. And a relay circuit is used to control the motor and LED of the flashing alarm light.

Bill of Material:

Product Name	Manufacturer	Quantity	Buy KitBuy Kit
LM555CN - Timer, Oscillator & Pulse Generator IC, TTL Compatible, Astable, Monostable, 4.5 V to 16 V, DIP-8	On Semiconductor	3	Buy NowBuy Now
LM317T -1.2V to 37V, 1.5A Adjustable Positive Voltage Regulator in TO-220-3 Package	STM Electronics	1	Buy NowBuy Now
G5V-1-DC5 -Signal Relay, 5 VDC, SPDT, 1 A, G5V-1 Series, Through Hole, Non Latching	OMRON ELECTRONIC COMPONENTS	1	Buy NowBuy Now
Ceramic Disc Capacitor, 0.01 µF, 100 V, ± 20%, 5 mm	Vishay	3	Buy NowBuy Now
Electrolytic Capacitor, Miniature, 10 µF, 25 V, 515D Series, ± 20%, Radial Leaded, 5 mm	Vishay	3	Buy NowBuy Now
Through Hole Resistor, 10 ohm, MF25 Series, 250 mW, ± 1%, Axial Leaded, 250 V	Multicomp	1	Buy NowBuy Now
Through Hole Resistor, 100 ohm, 250 mW, ± 1%, Axial Leaded, 250 V	Multicomp	1	Buy NowBuy Now
Through Hole Resistor, 1 kohm, 500 mW, ± 1%	TT ELECTRONICS / WELWYN	1	Buy NowBuy Now
Through Hole Resistor, 10 kohm, 500 mW, ± 5%, Axial Leaded, 350 V	MULTICOMP	4	Buy NowBuy Now
Through Hole Resistor, 68 kohm, MF25 Series, 250 mW, ± 1%, Axial Leaded, 250 V	Multicomp	1	Buy NowBuy Now
1N4007 -Standard Recovery Diode, 1 kV, 1 A, Single, 1.5 V, 30 A	MULTICOMP PRO	2	Buy NowBuy Now
Trimpot, Single Turn, Cermet, Side Adjust, 220 ohm, Through Hole, 1 Turns	Bourns	1	Buy NowBuy Now
Trimpot, Single Turn, Cermet, Top Adjust, 10 kohm, Through Hole, 1 Turns	Bourns	1	Buy NowBuy Now
Laser diode - 5mW, 650nm, Red - Module	Adafruit	1	Buy NowBuy Now
2.5 Inch 5.0W 4 Ohm Full Range Speaker, 66mm	Visaton	1	Buy NowBuy Now
ADVANCED PHOTONIX LDR, Photoresistor, 1 Mohm, 250 mW, 320 V	ADVANCED PHOTONIX	1	Buy NowBuy Now
Rocker Switch, SPDT, On-Off-On, Panel	ZF ELECTRONICS	1	Buy NowBuy Now
Pushbutton Switch, SPST, Off-(On), Round, Red	NTE ELECTRONICS	1	Buy NowBuy Now
Prototype Board, Phenolic, 30 x 25 grid, 1.6 mm, 94 mm, 71 mm	Multicomp	1	Buy NowBuy Now
BATTERY HOLDER 4 X AA, 6V, w/ switch, wire leads	OSEPP	1	Buy NowBuy Now

Additional Parts:

Product Name
Rotating LED Beacon Light
Case materials
Extra Wire
(4) AA Batteries

Top Comments

Parents

miles90 over 4 years ago

We should learn something from this.

Should every circuit be protected with a fuse ? Shall we add overcurrent protection on every project ? This should be done during the development process at least.

Are batteries the best choice ? Most of DC power supplies adapter have short circuit and overcurrent protections build-in. I would have burnt a lot these otherwise.

The 555 timer chip is not the easiest component to work with. That’s probably the reason why I do not use it very often. I’m a beginner in electronics and the 555 timer is still challenging for me.

I will search for documents and books about 555 timers and let you know.
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beacon_dave over 4 years ago in reply to miles90

"... the 555 timer is still challenging for me.
I will search for documents and books about 555 timers and let you know... "

Have you seen this episode ?
The Learning Circuit: 62: How 555 Timers Work
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miles90 over 4 years ago in reply to beacon_dave

Yes I did. I learned a lot of things, especially the two comparators story. I will look again to the PWM story. To me this is the most interesting application of the 555 timer.

Thank you.
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makerkaren over 4 years ago in reply to beacon_dave

Came here to say this. Like, I’ve done the most videos on 555 timers at this point. So many. But happy to help more if I can. They’re really good at what they do, so I find them very useful for when I want to only use discrete components and not a microcontroller.
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makerkaren over 4 years ago in reply to beacon_dave

Came here to say this. Like, I’ve done the most videos on 555 timers at this point. So many. But happy to help more if I can. They’re really good at what they do, so I find them very useful for when I want to only use discrete components and not a microcontroller.
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