Motor over current sensor

Thread Starter

Matt D.

Joined Nov 10, 2013
65
Thanks BR that is a really site. I like that it is interactive.
I still would like to know why there are the voltage ranges when the voltage is increasing or decreasing on the datasheet for an IC?
I would have thought it would be more specific.
 

BR-549

Joined Sep 22, 2013
4,938
Remember, that you were advised not to use a Schmitt trigger.

A trigger has two settings. First a positive setpoint and then a negative setpoint. These setpoints are not set by the chip. They have to be set by you, with an input voltage divider and a feedback voltage divider.

That's what the bottom example of link shows you how to set.

If you are determined to use that chip, google and study all you can on schmitt triggers.

You will need to invert the trigger action. You want the neg fall first...then the pos.

If you don't follow what I'm saying.............study the triggers first...........then ask questions.


Good luck.
 

Thread Starter

Matt D.

Joined Nov 10, 2013
65
When I first mentioned Schitt Max said that was going to be another suggestion. It is just that I have this IC on hand.
I don't understand how one would set the trip point. In a voltage divider with say a photocell does the voltage not slowly move in some cases? Therefore how is the voltage predetermined by you?

Your link? I don't see what you are talking about. I just see the main page with all the links.
I've researched the Schmitt triggers and have reached my understanding as far as I can go.
I think it is fair and legitimate question I've come here to learn and have researched first and now I'm stuck with that principle. I'm not trying to waste anyone's time. I'm not asking what Ohms law is.
 

BR-549

Joined Sep 22, 2013
4,938
In order to understand a schmitt trigger data sheet, you will need to study op-amps. A schmitt trigger, is just a particular op-amp configuration.

If you study op-amps, you will see that they may be configured many different ways. Several of the configurations can be used to preform your needed function.

For instance, Max suggested a comparator for your solution.

When you understand how they work, and how easy they can be to work with, you will be using them everywhere.

http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/opampvar.html
 

Thread Starter

Matt D.

Joined Nov 10, 2013
65
I'm not stuck on the Schmitt trigger and will look at the other IC Max suggested, however I would like to understand how one sets the trip point on the Schmitt trigger. I'm just not getting it and I'm not sure you are giving an explanation but rather giving other solutions.
Honestly are any of the links you provided will explain how you exactly set the trip point when the voltage is variable on the Schmitt trigger?
 

Thread Starter

Matt D.

Joined Nov 10, 2013
65
Apparently it is just a range the IC has and not something you set. And the positive going and negative going CAN overlap.
I finally found a publication by TI called understanding Schmitt Triggers.
Perhaps you might find it useful.
 

Thread Starter

Matt D.

Joined Nov 10, 2013
65
Yes I know what a voltage divider is and how if you use a CDS in place of one of the resistors then you will have a slowly changing voltage (like when used outside). The Schmitt trigger will keep the IC from ocillating because it has the hysteresis.
 

BR-549

Joined Sep 22, 2013
4,938
Sorry, no matter what I do, I can't get that link to copy, like I can the other links.

As I said before, both setpoints are controlled by voltage dividers. That you design.
 

BR-549

Joined Sep 22, 2013
4,938
Copy and search this on google.......it will give you the links.

"schmitt trigger site:hyperphysics.phy-astr.gsu.edu"
 

Thread Starter

Matt D.

Joined Nov 10, 2013
65
Sorry Cadium Sulfide cell. Photo resistor.
I don't think you can exactly set the setpoint.
Look at the document I mentioned,
 

BR-549

Joined Sep 22, 2013
4,938
I have read that document more then once, my friend. I thought we were taking about motor current.

If you want to teach me, I have some pretty deep questions.

And from your responses, I don't think I can teach you.

Good luck with your studies.
 

ronv

Joined Nov 12, 2008
3,770
Apparently it is just a range the IC has and not something you set. And the positive going and negative going CAN overlap.
I finally found a publication by TI called understanding Schmitt Triggers.
Perhaps you might find it useful.
No, they don't overlap. For a given power supply voltage and temperature there will always be separation.
But you are right, you cannot adjust them like with a voltage divider, so you have to adjust the voltage divider made by your CDS and a resistor (or pot) to match the thresholds of the IC.
 
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