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First try on laser alarm

Dr_Doggy

Well-Known Member
yes, if you can get a switch or button in there its much easier...

ok unhook buzzer and Ldr,
put meter on pin 3 and ground...
test resistor for resistance,
hook up resistor to pin 6,
hook up other wire on resistor to 9v ...
check pin3 ...
now take resistor from 9v and hook up to ground
check pin3 ...

..... this will test the chip
... if chip works then hook up buzzer and do test again
 

fixit7

Member
yes, if you can get a switch or button in there its much easier...

ok unhook buzzer and Ldr,
put meter on pin 3 and ground...
test resistor for resistance,
hook up resistor to pin 6,
hook up other wire on resistor to 9v ...
check pin3 ...
now take resistor from 9v and hook up to ground
check pin3 ...

..... this will test the chip
... if chip works then hook up buzzer and do test again
I am a bit confused.

If I put meter leads on pin 3 and ground, how can I test resistance of resistor?

You have probably done this many times, but may forget details that semi-newbies need.
 

fixit7

Member
I want to add this led and a switch to my breadboard so don't have to keep plugging in my power supply.

It has a built in resistor. Sorry, it did not come with a data sheet.

Will adding this add any complication to the laser alarm project?

118244
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
yes, very strange results.

take a pic of your breadboad.

Some breadboards have break in the "power" busses, some don't. In other words if this is a about a 3" x 8" bread board with two
busses" on the top and bottom. Those 2 busses might actually be 6. The outer two traces Corner to corner on the long edge is not continuous.

The one on this https://www.baldengineer.com/electronics-introduction-to-breadboards.html page isn't.

EDIT: 4 changed to 6 busses
 
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Dr_Doggy

Well-Known Member
lol.. leave the meter on pin3 & gnd power circuit and test the volts

use the resistor or one of your jumpers to hook up pin 6 to first power , then ground but not at the same time
 
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fixit7

Member
NOTE:
To Switch high power devices such as Relay, speakers etc use transistors to turn it on by drawing power directly rather than sourcing it from 555.

Is my circuit drawing power from the 555?
 

fixit7

Member
I think I have got it going. :)

I did not have all the pins going to Vcc.

And R2 is a 220 ohm resistor.

I substituted a 12 v led(with built in resistor) for the piezo buzzer.

With no laser light, the led lights.

With laser pointed at the LDR, led turns off.

Is that what it is supposed to do?
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
You need R1. It's not a critical value. During the time the output is going off, there is a momentary short through the timer ground to Vcc. This could definitely degrade the timer.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
Do you have any resistors close to 1K and (9-10K)?

remove R1 and R3 (Photocell).

Substitute around 1K for R1 and 9K for R3. Jumper R3 with a solid wire briefly to simulate laser light and 9K without.
 

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