You said the Vref = 1.49V and Vin=1.5V everything is fine, right?

Before you add 0.5V or 1.5V, please go to measure the voltage of Vin(+), how many volts is it?

Do you have add the 10K to gnd, if you have and then change it to 3.3K or less, I'm afraid that is the current flows out from the (+) of op amp and when the current flows through the 10K and then the Vin will get a as Vin = I*10K, so now you have to reducing the 10K.

 

As mentioned earlier it was 1.7v... however its only when I reduce the ref much lower than this to approaching 0.5 that it comes on without the battery attached..
Thanks
Will try lowering it tomorrow

 

You said the Vref = 1.49V and Vin=1.5V everything is fine, right?

Before you add 0.5V or 1.5V, please go to measure the voltage of Vin(+), how many volts is it?

Do you have add the 10K to gnd, if you have and then change it to 3.3K or less, I'm afraid that is the current flows out from the (+) of op amp and when the current flows through the 10K and then the Vin will get a as Vin = I*10K, so now you have to reducing the 10K.

On the ref voltage I know have 0.4 volts which is fine as I want to use a 0.5v to turn on the output. however, the led comes on without supplying any voltage. measuring pin 3 I get around .3 volt. Help !!

 

On the ref voltage I know have 0.4 volts which is fine as I want to use a 0.5v to turn on the output. however, the led comes on without supplying any voltage. measuring pin 3 I get around .3 volt. Help !!

Pin 3(+) is 0.3V and how many volts on pin 2(-) and pin 6(Vout) without led ?
How many volts of Vcc of op amp?

 

Pin 3(+) is 0.3V and how many volts on pin 2(-) and pin 6(Vout) without led ?
How many volts of Vcc of op amp?

vcc supply? 9v
pin1 3v
pin 2 .4v
pin 3 0.34v (with 680ohm resistor)
pin 6 7.98v
pin8 3v

Thanks for your help

 

vcc supply? 9v
pin1 3v
pin 2 .4v
pin 3 0.34v (with 680ohm resistor)
pin 6 7.98v
pin8 3v

Thanks for your help

What kind of the package do you used?
The Vcc and gnd of the circuit that I drawn was compatible with uA741, the pin 8 should be N.C. that it is no any voltage, unless the IC was damaged, do you have another same IC or try to use the other different ic to do the test, but be careful the pinout.

 

Hi
Its an mc34071p
tried another and the same
don't have any other ics
could buy some

 

I don't have mc34071p, so I used LM324 to tried, it's quite normal and it works as its function, when the pin(+) lower as 0.390V than pin(-) 0.396V then the output is low, when the pin(+) higher as 0.40V than pin(-) as 0.396V then the output is high.

If I only connected a 680Ω from pin(+) to gnd and measure the voltage of pin(+) and then there is no voltage at all.

 

Thanks
I will buy a lm324 - thanks for your help.

what software do you use for this?

 

Thanks
I will buy a lm324 - thanks for your help.

what software do you use for this?

You mean the circuit I drawn?
I used paint to draw it, I used all my own, if you want to use it then you can try the Wendy's version.
1. Introduction, and Paint as CAD.

If you mean what software to do the experiments, I just used breadboard to do the test.

 

Thanks friend...

how do you know what ICs to use - or do you just use what you have?

 

Thanks friend...

how do you know what ICs to use - or do you just use what you have?

It depends on what kind of the request, if the voltage higher than 0.1V then I will use what I have and usually use as LM324, I also prepared some other op amps as OP07, LM358, LF356, I also have some comparators as LM339, but I like to use the op amp to place the job of comparators, why I like to use LM324, because my previous ... previous boss given me over 50 pcs of LM324 when he end of his company, although LM324 is an old type IC, but it can be reach up to 1MHz, and it's general function is quite good, so the general purpose and many comparators can do also it can do, so I usually use LM324 to do the job of amplifying and comparing.

 

Ok - thanks
will let you know how I get on

 

lm324 you used - correct?
the last schematic shows mc34071?

 

lm324 you used - correct?

Yes.

the last schematic shows mc34071?

I forgot to change the IC number.