Hello All,

I'm trying to design a circuit that measured a voltage, compares it and if it is lower then a certain value, the output goes high, meaning i have a error.
So far so good...

my issue is how can i keep that error until i reset it ? the idea is that if the error output goes high a led will turn on indicating a error has occurred and it should only be turned off by manual reset.

Any idea about how can i implement this ?

Thank you all!

Best regards,
BD

 

Depending on the output levels, I’d use an SR flip flop. The output of your comparison circuit goes to the set input. Wire a push button to the reset input. Use the Q or Q’ output to drive your error indicator, depending on if a high or low output is an error. Maybe a CD4013 wired as an SR flip flop.

 

I'm trying to design a circuit that measured a voltage, compares it and if it is lower then a certain value, the output goes high

Schematic of your design. Please

 

As above, a flipflop. There are several options: two NAND logic gates, two NOR logic gates, two transistors, one-half of a dual flipflop chip, etc. Which one fits your available parts and skill set?

Also, what is the power source, and what will the output signal drive?

As above - schematic?

ak

 

Arduinos solve any thing.

Now whats the range of the voltage in,
what is the difference in voltage between good and bad
how fast are you looking to detect a drop, a us drop is more difficult than a minute drop

 

So this is my circuit as i have it ( ltspice file).
I'm going to look into SR latch to understand how to implement that.
I wanna do this fully analog , no microcontroller

 

So this is my circuit as i have it ( ltspice file).
I'm going to look into SR latch to understand how to implement that.
I wanna do this fully analog , no microcontroller View attachment 215915

Here’s a reference to building an SR Latch with either NAND or NOR gates.

 

What is the actual voltage trip point value you want to detect?

What is the complete range of input voltage values?

What is the output impedance of whatever is providing the voltage being sensed?

What power supply voltages are available?

ak

 

Hello All,

I'm trying to design a circuit that measured a voltage, compares it and if it is lower then a certain value, the output goes high, meaning i have a error.
So far so good...

my issue is how can i keep that error until i reset it ? the idea is that if the error output goes high a led will turn on indicating a error has occurred and it should only be turned off by manual reset.

Any idea about how can i implement this ?

Thank you all!

Best regards,
BD

What the circuit will need is a electronic “memory” element called a latch. This element can take different forms but a couple are made from discrete Transistors or an integrated circuit. The latch will need the capability to be “set” or “reset”.

 

What the circuit will need is a electronic “memory” element called a latch. This element can take different forms but a couple are made from discrete Transistors or an integrated circuit. The latch will need the capability to be “set” or “reset”.

Like the SR Latch in my last post.

 

I wanna do this fully analog , no microcontroller

It can be done with all analog components, but you want a logic output so things will be non-linear.

With that caveat, this can be done with one opamp (plus some supporting stuff) - depending on the answers to post #8.

ak

 

So this is my circuit as i have it

How is that comparator circuit using U1 going to operate if you are switching the V1 supply? The output of U1 is normally high with the + input at 3.5 volts and - input at zero. Every time the pulse switches on V1 and if that voltage at the - input is higher than 3.5v you will get a negative pulse.
Why do you need to switch V1?
Why not connect R3 directly to V1?
SG

 

How is that comparator circuit using U1 going to operate if you are switching the V1 supply? The output of U1 is normally high with the + input at 3.5 volts and - input at zero. Every time the pulse switches on V1 and if that voltage at the - input is higher than 3.5v you will get a negative pulse.
Why do you need to switch V1?
Why not connect R3 directly to V1?
SG

Im sensing the voltage of a battery. V1 allows to connect the voltage divider to the circuit only when i want to read the voltage.
The supply for the circuit is generated from another circuit.
This circuit is only to be switched from time to time to check the battery voltage.
The output signal polarity can be switched to what is more convenient.

Thank you

 

What is the actual voltage trip point value you want to detect?

What is the complete range of input voltage values?

What is the output impedance of whatever is providing the voltage being sensed?

What power supply voltages are available?

ak

I want to give the error signal when the battery voltage goes lower than 9.6 V( nor sure if that the exact value i have now on the circuit )
The battery voltage could swing from 12.4 to 9v .
I have a 5v supply for the circuit

Thank you for the help

 

Here’s a reference to building an SR Latch with either NAND or NOR gates.

Thank you for the refernce.
I'll check that out!

 

V1 allows to connect the voltage divider to the circuit only when i want to read the voltage

But do you understand what I was getting at? As long as V1 is above 9.6 volts then every time you go to check V1 U1 will output a negative going pulse. Once it's below 9.6 volts then the output of U1 stays high but it is normally high between readings.
How is that going to work for you?
SG

 

First pass. Missing decoupling, unused section pin treatment, etc. Many other rail-to-rail opamps should work.

ak

 

First pass.

That will work if Vbatt is connected continuously to R1.
But the TS said, "I'm sensing the voltage of a battery. V1 allows to connect the voltage divider to the circuit only when i want to read the voltage."
Did you look at his schematic in post #6?
The V1 or Vbatt battery to be monitored is not connected until switched on by Q1 and the FET, hence the output of U1 will always be high.
SG

 

thank you all for the feedback !
I'll try and post back when i have this working as planed !

 

my issue is how can i keep that error until i reset it ? the idea is that if the error output goes high a led will turn on indicating a error has occurred and it should only be turned off by manual reset.

That will work if Vbatt is connected continuously to R1.

Actually, it will latch the error state after the battery is disconnected, as requested.

My read of the #6 schematic is that the battery is V1, and is connected to the monitor through M1 when V2 pulses high. His trip point is 3.6 V. My trip point is 2.5 V with an input adjustment that covers the 9 V to 10 V input range. Disconnecting the battery has the same effect in both circuits - the output goes high, the error state. In my circuit the output latches there, so if the battery returns to the "good voltage range, the output continues to indicate that an error occurred.

But I can see where this might not be what the TS wants, per your question in #16.

ak