All About Circuits

Super sensitive intruder alarm

L

LesJones

Joined Jan 8, 2017
4,190
I think the LED is faulty or the wrong way round. Measure the voltage between ground and pin 1 of the LM358 with the beam clear and blocked.Post the results. also try adjusting RV2 so the slider is at the top end (Positive end.)

Les.
 
Audioguru

Audioguru

Joined Dec 20, 2007
11,248
The circuit is very poorly designed:
1) No part number for the IR receiver or module. It is probably a photodiode.
2) If the LED is red then its 1.8V forward voltage drop is too low for the 555 to be reset so it will not work. There is nothing limiting the LED current so the LM358 will probably burn it out, then the 555 will oscillate.
3) If the reset pin voltage on the 555 is high enough then it will produce an ultrasonic bat sound frequency of about 30kHz.
4) If the speaker is 8 ohms then the 1uF capacitor will feed it ultrasonic bat sounds above 20kHz.

Why not find a circuit that was designed properly by an expert?
 
Audioguru

Audioguru

Joined Dec 20, 2007
11,248
I should have looked up the reset voltage in the datasheet of the 555. Most circuits show the reset pin connected to the positive supply voltage.

I played the video but I could not understand the horrible Engrish. He sounds like the people who phone me every day from the other side of the world to sell "Duck Cleaning". I wonder why the ultrasonic beep from the simulated circuit sounded like a machine gun?
 
Audioguru

Audioguru

Joined Dec 20, 2007
11,248
Yeah, the 555 is not a power amplifier so it is overloaded when it drives an 8 ohm speaker. Since the power supply is missing an important bypass capacitor then the supply voltage droops and is amplified by the opamp which turns the 555 on and off like a machine gun.
 
AnalogKid

AnalogKid

Joined Aug 1, 2013
11,048
R6 is way too small. At 3 V (the max output of a 358 powered by 5 V) the 358 needs to source 23 mA into R6. It can't. My guess is that the output isn't getting up high enough to turn on D3.

Since the opamp is running as a comparator with a totem-pole output, what is the purpose of RV2 and R3? What is the adjustment supposed to do?

ak
 
-live wire-

-live wire-

Joined Dec 22, 2017
959
Unless you are using extremely precise instruments and control/amplifier circuits, you will not want it to be so sensitive. There are plenty of things that will influence the input like humidity, temperature, and other factors. You want it to set off an alarm if there is a significant change, like a person walking in front of the sensor. I would suggest either a motion/distance sensor with a micro-controller or a simple laser tripwire where if a person blocks it and the resistance increases, it creates a voltage divide that lights up the LED in series with buzzer, or uses a relay/transistor to do that. A 555 might not really be necessary here.
 
M

mufet

Joined Jan 11, 2018
8
You must log in or register to reply here.
Thread starter Similar threads Forum Replies Date
myall What determines the frequency of this super simple tesla coil circuit? General Electronics Chat 8
Z Super Capacitor Jump Starter Power Electronics 20
dcbingaman Super Accurate Resistor Fun General Electronics Chat 100
K Cannot change 90 Mhz FM receiver (SRR) to 16 MHz FM Wireless & RF Design 34
yash001324 i need a pcb circuit of super sensitive intruder alarm General Electronics Chat 6
Similar threads
What determines the frequency of this super simple tesla coil circuit?
Super Capacitor Jump Starter
Super Accurate Resistor Fun
Cannot change 90 Mhz FM receiver (SRR) to 16 MHz FM
i need a pcb circuit of super sensitive intruder alarm

You May Also Like

Top