I need a circuit that will convert an analog signal of up to 12 volts to a square wave of 0 to 5 volts. I tried to
simulate the circuit with LTSpice using different values for HiRef and LoRef but it failed. I attached the circuit
schematic. I hope someone can help me with this.

thanks

 

Since the outputs of an LM339 are open collector, the diodes are unnecessary. They are backwards in your diagram and will never result in a low output.

 

Here is how a "Window Comparator" should work. V(in) can be other types of waveforms.

 

An LM339 can only sink current. No current flows OUT of the output. Therefore no current can flow through your diodes.
Try turning them round.
I don't understand your description of what you want your circuit to do, but it looks like a window comparator to me.

 

Tha

Here is how a "Window Comparator" should work. V(in) can be other types of waveforms.
View attachment 349205

Thanks man this is great. When I run the sim on my pc it is missing the symbol for the LM339. I don't know how to
set up a symbol.

 

Thanks man this is great. When I run the sim on my pc it is missing the symbol for the LM339. I don't know how to
set up a symbol.

I think perhaps my LM339 model in LTSpice is faulty as well.

 

An LM339 can only sink current. No current flows OUT of the output. Therefore no current can flow through your diodes.
Try turning them round.
I don't understand your description of what you want your circuit to do, but it looks like a window comparator to me.

Hi

I want to be able to feed an analog signal in and get a square wave out. Yes, a window comparator is what
I was thinking.

 

Depending on exactly what You are trying to accomplish,
a 7555 Chip may be the simplest solution.
It Flips and Flops at 1/3 and 2/3 of the Supply-Voltage, maybe that'll work for You.
.
.
.

 

Depending on exactly what You are trying to accomplish,
a 7555 Chip may be the simplest solution.
It Flips and Flops at 1/3 and 2/3 of the Supply-Voltage, maybe that'll work for You.
.
.
.

Thanks. I will look into that!

 

Thanks. I will look into that!

Below is the LTspice sim of a circuit using the 555 as suggested by LQC:
The output goes high when the TRIG input drops below 1/3Vcc (1.67V) and goes low when the THRS input goes above 2/3Vcc (3.33V)

 

I've collected the files you need in a .zip file including the symbol and the sub-circuit. Extract all four files into a folder and see if it runs.

 

Hi

I want to be able to feed an analog signal in and get a square wave out. Yes, a window comparator is what
I was thinking.

That gives an output frequency that is twice that of the input signal.
A comparator with hysteresis (555 type as per @LowQCab) gives and output at the same frequency.
This
http://sim.okawa-denshi.jp/en/compkeisan.htm
helps you design a comparator with hysteresis

 

You say the signal is “up to 12V.” What should your circuit do when it is 1V? What if it goes negative? What waveform(s) might it be?

What is the frequency and duty cycle of the square square wave output

Is this for an actual project, a homework assignment, or just for learning?

In any case, a better specification of the input and output is needed.

 

I've collected the files you need in a .zip file including the symbol and the sub-circuit. Extract all four files into a folder and see if it runs.

Thanks Papabravo!

 

Below is the LTspice sim of a circuit using the 555 as suggested by LQC:
The output goes high when the TRIG input drops below 1/3Vcc (1.67V) and goes low when the THRS input goes above 2/3Vcc (3.33V)

View attachment 349218

Thanks!

 

Thanks!

I appreciate all of the responses. After giving this more thought, I have come up with what I believe to
be a set of specs for the circuit based upon your responses.

1) Attenuate the input voltage if it is above 5 volts.
2) Amplify the input voltage if it is below 3.3 volts.
3) Accept any type of waveform, ac or dc, from 1 Hz to 60MHz.
4) Protect the circuit from negative voltages and voltages say above 15 volts.
5) Provide a 5 volt square wave output with the same frequency and phase as the input.
6) Low noise output suitable for digital circuit interface.

Probably a pretty tall order.

 

3) Accept any type of waveform, ac or dc, from 1 Hz to 60MHz.

That will require some very high speed digital gates such as the 74AC series.

5) Provide a 5 volt square wave output with the same frequency and phase as the input.

How do you define phase if the input is not sinusoidal?
That would be very difficult to do at 60MHz.

 

Probably a pretty tall order.

That is the understatement of the year.

Why are you doing this?

 

I did have second thoughts that possibly the TS was wanting a voltage to frequency converter. But now it seems more like an input circuit for a frequency counter. That would be a good place to look for a sample circuit . My HP counter works with about 100mV to several volts.

 

I did have second thoughts that possibly the TS was wanting a voltage to frequency converter. But now it seems more like an input circuit for a frequency counter. That would be a good place to look for a sample circuit . My HP counter works with about 100mV to several volts.

Would this circuit work? Not sure what voltage should be used for VCC?