PIC + Cny70

M

moonstreat

New Member

• May 3, 2010

• #1

good ..
I've got a serious problem, I assembled the following schedule:

**broken link removed**

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I am after the test did not work in my PIC16F876A because there its output voltage is too low, sometimes does not reach the 2V,

Somebody help me?

 

Last edited: May 3, 2010

MikeMl

Well-Known Member

Most Helpful Member

• May 3, 2010

• #2

The LM358 is a pretty bad op-amp, especially when you run it off a single +5V Supply! When you ask its output pin to source more than a couple of mA, it will only pull the output to about 2.5V.

It is better at sinking current than sourcing current. It will pull the output pin to ~100 mV when sinking 10mA. I suggest you reverse the inverting and non-inverting inputs, and connect the LED and its current limiting resistor between the output pin and the +5V supply. Or buy a modern rail-to-rail op-amp which is capable of sourcing and sinking > 20mA.

 

Last edited: May 3, 2010

M

moonstreat

New Member

• May 3, 2010

• #3

you can post me a circuit that works? I do not know what to do this

 

crutschow

Well-Known Member

Most Helpful Member

• May 3, 2010

• #4

Deleted message.

 

Last edited: May 3, 2010

Boncuk

New Member

• May 3, 2010

• #5

Hi moonstreat,

try this one.

Boncuk

 

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blueroomelectronics

Well-Known Member

• May 3, 2010

• #6

Why not use one of the built in comparators?

 

Boncuk

New Member

• May 3, 2010

• #7

blueroomelectronics said:

Why not use one of the built in comparators?

Click to expand...

There is nothing much to compare. The input will either be low or high.

Hans

 

blueroomelectronics

Well-Known Member

• May 4, 2010

• #8

You could then drop the external comparator. No extra ICs needed.

 

Last edited: May 4, 2010

MikeMl

Well-Known Member

Most Helpful Member

• May 4, 2010

• #9

moonstreat said:

you can post me a circuit that works? I do not know what to do this

Click to expand...

Here is how I would do it. I didn't have a sim model of your exact opto coupler, so you may have to optimize R20 and R40 for the specific one you are using. To simulate some variation in the light reaching the photo-transistor, I vary the current in R20. I have turned the comparator upside down to take advantage of its current sinking capability. I have also added some positive feedback R1 to prevent chattering (oscillation near the trip point).

 

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Last edited: May 4, 2010