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Help with circuit please

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Hi every1

I recently build this circuit:
Battery Powered Night Lamp | FREE Electronics Circuit Schematics Diagrams

I think all my wiring is correct. The problem is the circuit activates when the LDR is in light and not in the dark like it's indicated.
What I made out so far is:
If the LDR is in light the ohm's is low and current can flow.
If the LDR is in dark the ohm's is high and current can't flow.
Am I correct? If that's the case how can I trigger it?
Hope there's a simple way of just switching 2 components around or so.

Also, for C2 I didn't have a 25V Cap.
I used a 16V.
How much will this affect the circuit? Or will it only effect the output voltage?
Also I used a 1N4148 for D2

I want to use this as night light's around the house seeing that it can run quite long on a AA battery(If the circuit works?)
I have looked at a few drawings on how they trigger the 555 cmos but I get confused from all the different opinions ect.
 

ericgibbs

Well-Known Member
Most Helpful Member
Hi every1

I recently build this circuit:
Battery Powered Night Lamp | FREE Electronics Circuit Schematics Diagrams

I think all my wiring is correct. The problem is the circuit activates when the LDR is in light and not in the dark like it's indicated.
What I made out so far is:
If the LDR is in light the ohm's is low and current can flow.
If the LDR is in dark the ohm's is high and current can't flow.
Am I correct? If that's the case how can I trigger it?
Hope there's a simple way of just switching 2 components around or so.

Also, for C2 I didn't have a 25V Cap.
I used a 16V.
How much will this affect the circuit? Or will it only effect the output voltage?
Also I used a 1N4148 for D2

I want to use this as night light's around the house seeing that it can run quite long on a AA battery(If the circuit works?)
I have looked at a few drawings on how they trigger the 555 cmos but I get confused from all the different opinions ect.

hi,
The LDR is connected to the 555 RESET pin, if the pin is low the 555 is RESET.
When high the RESET is removed and the circuit works.

The LDR is acting as a resistor.

The 16V cap will not affect it, the 4148 has a higher voltage drop than a schottky diode, should be OK
 

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That I understand but like I said when it's light the circuit works and when it's dark it doesn't. Here is the pictures from Lochmaster.
8898-NightLight.jpg

8899-NightLight1.jpg


The 2 white dots on the left is where I connected the LDR. And the white dots on the right is the supply. Did I wire it wrong?
 
Last edited:
Sorry, the white dot on the right is the - for the LED and the minus sign is the - for the circuit. I used the white dot on the right at the + sign for supply to the circuit and the LED.
 

ericgibbs

Well-Known Member
Most Helpful Member
That I understand but like I said when it's light the circuit works and when it's dark it doesn't. Here is the pictures from Lochmaster.

The 2 white dots on the left is where I connected the LDR. And the white dots on the right is the supply. Did I wire it wrong?

hi,
Your layout looks OK.:)
Do you have a voltmeter.??
If yes, measure the voltage between pin4 and 0V , dark and light and tell us what you measure.

If you dont have a voltmeter, remove the LDR, does the LED now flash/light.?

Now connect a short link of wire from pin 4 to 0V, the LED should stop flashing.

Lets knw what you see.
 

ericgibbs

Well-Known Member
Most Helpful Member
Ok when in light, normal room light it measure's +- .960 VDC
And when I cover the LDR +- 1.508 VDC

hi,
The 0.96V is higher than the required typical RESET level, so the LED will always be ON.
At 1.5Vbatt I calculate you require 0.8V for a typical RESET.

Trying increasing the R3 [47K] to say 56K or 100K.

BTW: I assume you are using a CMOS 555 as the designer states.
 
Last edited:
Yip, using a CMOS. Ok will get the bigger resistors at home tonight and solder it on tomorrow at work and post my results. One thing I forgot was when I build the circuit I had my pin out wrong. I had the pins on the left of the 555 starting at the top with 5 6 7 8 not at the bottom 5 6 7 8 Could this maybe have damaged the timer? I think I tested it once or twice and not for long periods? I then discovered my simple mistake and corrected it?

Thanks for the help so far. Will give an update tomorrow. Almost time to go home. Will try doing it tonight otherwise tomorrow.

Thanks
 

ericgibbs

Well-Known Member
Most Helpful Member
Yip, using a CMOS. Ok will get the bigger resistors at home tonight and solder it on tomorrow at work and post my results. One thing I forgot was when I build the circuit I had my pin out wrong. I had the pins on the left of the 555 starting at the top with 5 6 7 8 not at the bottom 5 6 7 8 Could this maybe have damaged the timer? I think I tested it once or twice and not for long periods? I then discovered my simple mistake and corrected it?

Thanks for the help so far. Will give an update tomorrow. Almost time to go home. Will try doing it tonight otherwise tomorrow.

Thanks

hi,
If the supply polarity to the 555 was reversed when you had it 'crossed over' its highly likely its dead.:( fingers crossed.
 
hi,
If the supply polarity to the 555 was reversed when you had it 'crossed over' its highly likely its dead.:( fingers crossed.

I think I'm gonna change the 555 tomorrow. Just to make sure.
I'm gonna use the 100K. Don't have a 56K.
Will give an update as soon as I'm finished with it.
Hopefully I will get LED's this Friday after work.
Would really like to test this circuit over the weekend.

Thanks again Eric.
Appreciate it!!
 
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