[SOLVED] lm339 output problem........................................... ...

[kdg007]

I am trying to amplify the signal from photodiode(used LED as transmitter) using the comparator.as you can see,i have used 1M pot for the -ve terminal.I have checked the voltages of both inputs of comparator before giving the signal , 0.5v at -ve input and 0.5v at +ve input(using the 100k pot,i have changed the voltage).I am unable to get the desired signal at output pin.

Signal from frequency generator -> 5v/div (1cm block in CRO)
signal from photodiode -> 50mv/div (1CM BLOCK IN CRO)

please help !!! is something i am missing ?

thanks in advance.

 

[betwixt]

The output is connected to 0V !!!
I'm sure this is an error in drawing the schematic but if you correct it we can look further.
Do you need the negative supply?
What is the real load on the output?

Brian.

 

[kdg007]

its a schematic mistake,sry about that, the output is not connected to 0V.
i am a newbie in this,i am not sure what u mean by negative supply,do u mean the photodiode connected to the inverting terminal ?
i want the ouput to be square wave .


thank you.

---------- Post added at 17:17 ---------- Previous post was at 17:02 ----------

the output load is showing 5v... but i am not getting any signal.

 

[albbg]

Please check the pin-out. Pin 6 is the inverting input, pin 7 is the non-inverting input. In your schematic pin 6 and pin 7 are exchanged. Furthermore I can suggest you to place an high value resistor (rouhgly 1 Mohm) between output and non-invertin input, in order to have some hysteresis the help to avoid unwanted oscillations when the signal stays close to the reference voltage.

 

[kdg007]

is this right schematics?
-
i have reversed the position of the photodiode just to check,i am getting a square wave ,but is this the right procedure for the safety of the circuit ?
-
also,y specific value of 1M for output to nin-inverting input??

 

[kdg007]

D1,has been reversed upside down... forgot to change it in the picture

 

[albbg]

Can be OK, but it should works also with the diode in the original position, that is better since the reverse bias decreases the diode capacitance. You can try to change the 1M pot with a 100 k pot and regulate it until you see the squarewave.