The 555 IC Timer in an LDR curcuit board(Light sensitive trigger)

[Kartik.]

Can somebody lower the high level explanation of the 555 Timer IC in a light sensitive trigger

Heres the text,
Contrary to the normal use as an astable multivibrator, the 555 IC in this circuit functions as a comparator. To explain this rather unusual application,it is necessary to note the operations in the 555 IC - The output goes high upon the receipt of a trigger pulse at input pin 2. This pulse is of the voltage which is 1/3rd of the supply voltage.The output goes low again when the voltage at the second input pin 6 becomes 2/3rds of the supply. In the present design the second input is not used but the output of the chip can none the less revert the low state, since pin 6 is directly connected to the positive rail."

 

[Harald Kapp]

Show us the circuit, please.

 

[Kartik.]

http://4.bp.blogspot.com/_0wmbdDXZD.../AxGTjrewcvw/s320/light+sensitive+trigger.JPG

 

[Kartik.]

Thats the original one i have
right now i can provide you with the laterally inverted version of it only

 

[gorgon]

What is it you don't understand?
This circuit works as a comparator. If the pin 2 get below 1/3Vdd the output(3) goes high, If the pin(2) get above 1/3Vdd, the output(3) goes low. To do this the input pin6 must be higher than 2/3Vdd. On your last (reversed) drawing pin7 is pulling pin(6) low when the output is low. I don't know if this is necessary for the function, but you will introduce a small delay when the output is switching.

The function is just like any comparator circuit, with a output driver.

TOK

 

[Harald Kapp]

As I understand it:
This circuit uses only only one of the comparators built into the 555. If the voltage at TRIG is less than 1/3 Vcc (bright light), the internal FlipFlop of the 555 is set, the output goes high, the relay is turned off.
If the voltega at TRIG is more than 1/3 Vcc (dim light), the internal FlipFlop of the 555 is reset due to pin THRES being at more than 2/3 Vcc (it is connected to Vcc). Thus the output goes low and the relay is turned on.

Harald