Imagine I have a square wave that's either 5V or 0V, is there a way I can make it 2.5V or -2.5V?

 

Hello,

When the square wave is 50% on and 50 % off, then you may use a C-R network.
If it is not 50/50, you can subtract 2.5 Volts using an opamp adder circuit.

Bertus

 

Yes inputting into an op amp with a half supply offset.

 

Hello,

When the square wave is 50% on and 50 % off, then you may use a C-R network.
If it is not 50/50, you can subtract 2.5 Volts using an opamp adder circuit.

Bertus

It is, but it would take 120ms to center, and it can't take that long.

I thought about the opamp but I thought it wouldn't be able to reproduce negative voltage if it has 0V on V-.

 

Hello,

An opamp with dual powersupply can produce negative signals.

Bertus

 

I thought about the opamp but I thought it wouldn't be able to reproduce negative voltage if it has 0V on V-.

How is the circuit being powered?

 

How did you arrive at 120ms?
It depends on the C and R values chosen.

 

If you are trying to find the mid-voltage of your guitar signal you don't need a negative supply.

 

If you are trying to find the mid-voltage of your guitar signal you don't need a negative supply.

In multi sim, just an example for the frequency, resistance and capacitance I had, the point is, it would take some time.

How is the circuit being powered?

Just 9V, I don't have any negative voltage, that's the problem.

 

Use a 9V supply.
Create a 4.5V bias point by using a voltage divider with two 10kΩ resistors.
Use this to bias your input signal. Use a 1μF coupling capacitor. This will give a time constant of 5ms.

 

Use a 9V supply.
Create a 4.5V bias point by using a voltage divider with two 10kΩ resistors.
Use this to bias your input signal. Use a 1μF coupling capacitor. This will give a time constant of 5ms.

I tried to bias the square signal, can't get it to work.

I only can get the flip flop to output 5V (in this simulation), so I reduce that to 1V before the capacitor, after that the signal gets all screwed up.

 

Just 9V, I don't have any negative voltage, that's the problem.

If it's a 9 volt battery, you can use another for a negative supply.

Otherwise, you can use a voltage inverting switching regulator.

From On-Semi app note using the venerable MC34063:

 

It is, but it would take 120ms to center, and it can't take that long.

How much time do you need?

I thought about the opamp but I thought it wouldn't be able to reproduce negative voltage if it has 0V on V-.

You're right. It can't unless you cheat and use AC coupling.
In my opinion, the simplest way to bypass all that nastiness is to determine how much current your load needs when the output signal swings max negative and to use a negative supply which can supply that current.

 

It is, but it would take 120ms to center, and it can't take that long.

If this is for your divide by 2 audio circuit, the output will be going between 0V and 5V in a somewhat random fashion so I don't see that the initial settling time of the RC circuit is a significant factor.
You are unlikely to hear the effect.

 

If this is for your divide by 2 audio circuit, the output will be going between 0V and 5V in a somewhat random fashion so I don't see that the initial settling time of the RC circuit is a significant factor.
You are unlikely to hear the effect.

+1
Agreed. We are showing you how to bias the input to ½ supply voltage.
Will this work to shift musical notes to a lower octave? I don't think so.

The way to do this is to use a DSP (digital signal processor) and do the frequency shift digitally.
This allows you to do other effects such as adding chorus.

 

If this is for your divide by 2 audio circuit, the output will be going between 0V and 5V in a somewhat random fashion so I don't see that the initial settling time of the RC circuit is a significant factor.
You are unlikely to hear the effect.

Just affraid that it will mess with my amp, but I guess those values won't be high enough. I mean everytime I play a note, that effect happens, so it might saturate (clip the signal) or something.

 

+1
Agreed. We are showing you how to bias the input to ½ supply voltage.
Will this work to shift musical notes to a lower octave? I don't think so.

The way to do this is to use a DSP (digital signal processor) and do the frequency shift digitally.
This allows you to do other effects such as adding chorus.

I prefer analog effects, I like to learn the basics and put it to work ahah. Also they have more quality (not in this case ofc).

Just out of curiosity and slightly off-topic, by DSP you mean like an arduino?

 

I prefer analog effects, I like to learn the basics and put it to work ahah. Also they have more quality (not in this case ofc).

Just out of curiosity and slightly off-topic, by DSP you mean like an arduino?

By DSP, I mean a microcontroller. Arduino does not have the speed to do this. You need a faster MCU.

 

How about this?
I don't think the initial transient will be something you can hear.

 

There are dedicated charge pump ICs that can turn +9V into around -8 V with a lot less effort and noise than a traditional switching regulator. Since you don't need for the negative voltage to be regulated and the current requirement is very low, a 555 plus 6 external components (1 R, 2 D, 3 C) will be fine for this. Once you have an opamp powered by +/- V, the waveform can be shifted a fixed DC amount and will stay put no matter what the duty cycle or frequency, with no startup offset.

ak