hi ,,

can i use neon lamp as in fig below with any photo sensor like LDR to know if the Ac 220v/50Hz source switched on or off ?






thank you

 

That should work just fine. make sure external light cannot get to the LDR, just the light from the neon lamp.
It may be worth adding a capacitor across R2 so you get a more steady signal.
Are you using a commercial Neon lamp or wiring it yourself? Just remember to be VERY careful around mains!

 

just one point .... Neon has a very specific spectrum , mostly in the red , is your LDR sensitive to this ?? if the neon and LDR are very close it will probably be OK.

 

I've used that set-up. It works very well, using a bog-standard LDR. As Dendad suggetsed, use a capacitor across R2.

 

That should work just fine. make sure external light cannot get to the LDR, just the light from the neon lamp.
It may be worth adding a capacitor across R2 so you get a more steady signal.
Are you using a commercial Neon lamp or wiring it yourself? Just remember to be VERY careful around mains!

i want to buy the lamp and ldr and put them in black tube or cover them using heatshrink ^^
if i want to connect the output of the circuit to interrupt pin of any micro-controller should i modify the circuit ? or adding the capacitor across R2 enough?

regards

just one point .... Neon has a very specific spectrum , mostly in the red , is your LDR sensitive to this ?? if the neon and LDR are very close it will probably be OK.

i will put them as close as possible ^^

 

I've used that set-up. It works very well, using a bog-standard LDR. As Dendad suggetsed, use a capacitor across R2.

1uF enough ?

 

if i want to connect the output of the circuit to interrupt pin of any micro-controller should i modify the circuit ? or adding the capacitor across R2 enough?

To work a uC input the voltage must cross the input thresholds and by selecting the resistor value that should be possible, especially if you make sure all external light is excluded.

 

1uF enough ?

Depends what you want the micro to do in response to a light level change. If R2 is 10k then I'd use 10uF to give a time constant longer than the mains cycle.

 

thank you all

 

Hi ,

I tried the circuit with 10uf ,it worked fine .

But when I used push button with indication lamp across it the neon lamp became on, even the button not pressed .

Also I tried to use 220v coil relay to get logic signal .. it worked fine but if button has an indication lamp across it the relay became on when the button pressed or not .

Can I solve this problem ?

Thank you

 

Use a spare contact on the relay for the indicator lamp.
The slightest leakage current will light the Neon.
Max.

 

The problem :There are 5 buttons in parallel each one with indication lamp across it.. and the buttons about 5-15 meters from the circuit .



Thank you