[ window voltage comparator ]

[texane]

Hi,

As a beginner, I am reading the following book: practical electronics
for inventor, from Paul Scherz.

For a light sensor project, I need a window voltage comparator. I use
one from the above book. I attached the schema.

What should happen:
Vout is +5v when 2.3v<Vin<2.7v
Vout is 0v otherwise.

However, I get the opposite...:
Vout is 0v when 2.3v<Vin<2.7v
Vout is 5v otherwise.

I use a lm339 quad comparator, so that I actually has only one
comparator. I tested the comparator inputs/outputs independently
to see if it works, and I get right measures. Maybe there is something
I didnot understand regarding the above schema...

Any idea?

Thanks for helping,

Regards,

Fabien.

[texane]

I think I misunderstood something... the schema
actually works as expected, sorry for posting

[Simon]

if you get a similar situation again (thats if it really happens) reverse the inputs on the comparators