Light measurement

[Arouse1973]

A 741 is specified for a minimum of + and - 9V. And the extent of the outputs can be as bad as 3V from V+ and V-. So, with a 9V single sided supply, you can only expect the output to swing is from 3 to 6V.

I agree with Kris, either a 358 with +7v or more or a rail-to-rail opamp. I would go with the latter, Microchip makes some very good ones that I have had no problem with.

Bob

Hi Bob

I do agree with you both another op-amp would be better, Sometimes is nice to get on with something you have been working on for a while rather than waiting another day or so for the postman. It's nice to offer alternatives with the components they have. If he had more than one 741 then this could be done easily and A/D scaled down for sensing. He could get 29mV steps on a 10bit if he wanted. Probably more than enough.

Where did you find the info of minimum voltage of +/- 9 V. Max is +/-18 V for 741C and +/-22 V for 741 and 741A. I am just interested I didn't know that.

Cheers
Adam

 

[Iggnasp]

Hi Adam again. Whats is VF1 and VF2 I think VF1 is Led voltage range which get from light but I not to sure about VF1 if you can please tell me.

 

[Arouse1973]

Yeah sorry I should have removed VF1 and labelled VF2 as output. It was a modified circuit from a previous design.
Cheers
Adam

 

[Iggnasp]

Okey. You also worked with light sensor?
Ignas

 

[Arouse1973]

Many times
Adam

 

[BobK]

Where did you find the info of minimum voltage of +/- 9 V. Max is +/-18 V for 741C and +/-22 V for 741 and 741A. I am just interested I didn't know that.

Hmm, I thought I saw that and now I cannot find it. Another data sheet said 5V to 40V for the power. I guess I was wrong. I cannot imagine it would be very useful at 5V, seeing as the outputs cannot get close to V- or V+

They are always characterized only at + and - 15V, so anything goes at any lower voltage.

Bob

 

[Iggnasp]

Adam I have for you another question. Maybe you know about it. When I measure light and generate to electric signal and I need that result it will be insensitive. I think about electrolytic capacitor in output. But I really to sure or it's good ideas.
Ignas

 

[Arouse1973]

Sorry I didn't understand your question. What do you mean insensitive?
Adam

 

[Iggnasp]

How to adjust the sensitivity of the sensor outpu when you measure?

 

[Arouse1973]

Increasing the feedback resistor will do this.
Adam

 

[Iggnasp]

Hello everybody again I get a LM758 operational amplifiers. Maybe someone can offer schematic with this amplifier and led light measurement?