Voltage Sensing Circuit for Low Voltage Values

Thread Starter

Deve

Joined Dec 28, 2015
95
This should be an accurate representation of the circuit. Now for the fun part trying to meld the three circuits on to one board. The last two schematics on the page I will put together on one board and add a few things concerning the oil pressure warning and alternator circuit.

Low Fuel Warning Schematic:
http://devestechnet.com/Images/Projects/WarningSystem/LowFuelWarningCircuitSchematic.jpg

Entire Writeup:
http://devestechnet.com/Home/WarningSystem

Once again, thanks for the help. I would like to learn how to use LTSpice and it would be awesome if they had a tutorial circuit that were included. Currently there is a mental disconnect that I will have to work on somehow to get over the learning curve.
 

MikeML

Joined Oct 2, 2009
5,444
There are several LTSpice tutorials on the web, including at Linear.com

You left out the series resistor between pin 3 and the sender. That must be there to create the hysteresis, and to provide a modicum of protection for the opamp in case of a miswire...

You need to deal with the unused half of the LM358. Not good to leave the inputs floating... Read post #9 of this previous thread. I would tie the non-inverting input of the unused opamp to 2.49V, and then wire its output to its own inverting input.

Minor bitch: If you go to a forum, ask for help, someone steps up and does the entire design for you, it is bad form to present it on your own web site as your original work...
 
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Thread Starter

Deve

Joined Dec 28, 2015
95
So Pin 5 (+) to the 2.49 point, then pins 6 (-) and 7 (output) together? Thanks for catching that.
 

Thread Starter

Deve

Joined Dec 28, 2015
95
Website programming is HARD and something I picked up last year. You have a plan before starting any articles and part of the plan is to get all of the Credits for the entire article in once the Article is completed. That way I have time to sit and think about who I could have missed, etc. My website is something like nobody has ever seen in that it features new ideas and takes them all the way to fruition and then gives the information away freely. I don't make much money that way, but I meet more friends that way. If you doubt my honor, look higher in the article and you will see another schematic where I credit ElectronicsNMore. You just have to wait your turn to get the accolades. :) DONE!

Is the circuit fixed now Mike? Since your name is on it, I am very hopeful that you will also take the responsibility for making sure it's going to work as advertised. Thank you!
 

MikeML

Joined Oct 2, 2009
5,444
The circuit looks ok now. I would be for actually putting this in a car and driving around with it. I worry that the LED will flash a lot as the tank empties due to sloshing of the fuel.

If that is problem, we can increase the hysteresis (which will minimise the flashing). You could also use the other half of the opamp to make a slosh filter such as I talk about here (post #8).
 

Thread Starter

Deve

Joined Dec 28, 2015
95
Yup. response #8. One of the problems I run into is I have no vehicle to actually test it on. The cab is sitting on the floor! So I will take it that this is solid enough to proceed in the manufacturing of the PCBs and hope for the best. Or, we could err on the side of caution? Problem is, that discussion was a little over my head Mike. I'm trying, but learning is a process.
 

Thread Starter

Deve

Joined Dec 28, 2015
95
In my overall circuit, there are four total LED's (all the same) and yet I have four different resistor values. [the resistor that always accompanies an LED] Are they different as a product of the circuit being different, or the designer just putting in a wide variety of numbers? They span from 330-1200. I am at the stage where I am questioning each (questionable) component so I get this right.

On the slosh filter, my starting question would be, where at the comparator to connect, pins 1,2 or 3, and is it as simple as replacing the 10K with two 470K's and a few capacitors? The way it behaves on the bench, I cannot see that being a problem, but I do not always trust myself either.
 

Thread Starter

Deve

Joined Dec 28, 2015
95
Mike, now that you have had time to think about it, do you think we should include a slosh filter or no? I have spent the weekend building a soldered version of the entire system. The Oil Pressure warning system, the Water Temperature warning system which is quite complicated but now I am ready to solder the circuit you worked on. So far everything is working together well.

Once I get the soldered version together and each system works I will start learning how to use Diptrace and get this to a PCB maker.
 

#12

Joined Nov 30, 2010
18,224
If you want I can provide you ( for free) schematic and prog (in C) allowing you to set blink at any voltage level.
Let me know.
A microprocessor and C language programming to simulate a high quality zener diode and an op-amp?
I bet you hold focus groups to decide which shelf to put the milk on in the refrigerator.
Why do you always want to complicate the hell out of simple things that can be done with 1 or 2 chips?

@Deve
If you want to change your dashboard lights to LEDs, I have a 2 chip circuit to do that, too.
 

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Picbuster

Joined Dec 2, 2013
1,047
A microprocessor and C language programming to simulate a high quality zener diode and an op-amp?
I bet you hold focus groups to decide which shelf to put the milk on in the refrigerator.
Why do you always want to complicate the hell out of simple things that can be done with 1 or 2 chips?

@Deve
If you want to change your dashboard lights to LEDs, I have a 2 chip circuit to do that, too.
Your method works fine no problem with that.
Using my method gives you flexibility allowing thresholds modifications on the fly and activate free pins when needed.
And is build from a few components also.
With the milk yes a huge problem the bottle is to high for the shelf I want to put it on.(smile)
 
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