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DC signal to AC signal

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im_in_asia_now

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I've been thinking about how to change a DC signal (from 0 to X volts) into an AC signal (from (-X/2) to X/2 volts).

Instead of connecting the load between the DC signal and ground, I considered connecting the load between a DC signal and a second DC voltage (X/2).

Ok, so going off of a DC signal project everybody's familiar with, I tampered with a 555 circuit, using a ~50% duty cycle (http://www.electro-tech-online.com/...quare-wave-pulses-have-a-50-duty-cycle.94231/) and finally came up with this:

555 AC square wave.JPG

The signal is taken from between R1 and R2 and is an AC square wave at about -4 to 4 volts, where the original DC square wave is about 0 to 12 volts.

And I realise, this is just a simulation. So if this wouldn't really work in practice, by all means just let me know.

555 AC square wave osc.JPG

An explanation of the extra parts:

D1 is used to achieve a ~50% duty cycle
D2 is used to prevent a negative voltage on 555 pin 3 (not sure if this is even necessary, and it reduces the final output voltage)

R1 and R2 are the voltage divider network to create the AC square wave.

V2 is a negative voltage source, not sure if this will even work correctly in practice.

R3 is used to prevent a short between pos and neg terminals of the two voltage sources.

Please share your thoughts:

How much does this idea suck and what are some other ways to change a DC signal into an AC signal?

How ineffecient is this setup (where does it waste too much power) and what are the most obvious ways to improve it (if its worth improving on)?

Thanks

edit: asc:

View attachment 555 AC Square Wave.asc
 
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im_in_asia_now

New Member
I don't see how a Voltage to Frequency Converter could change a DC square wave to an AC square wave...

I could use an oscillator and a shmitt trigger to create an AC square wave, but I was considering how to change a DC signal into an AC signal of the same shape. Is changing DC signals to AC signals just something that has no use?

No feedback on the 555 AC square wave circuit?
 
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im_in_asia_now

New Member
I'm not planning to build it into a larger circuit, I was just interested in some ways to manipulate signals. Just basic electronic geek curiosity.
 

smanches

New Member
Doesn't a cap block DC but let AC pass? That's all I know. :p
 

ericgibbs

Well-Known Member
Most Helpful Member
I don't see how a Voltage to Frequency Converter could change a DC square wave to an AC square wave...
I've been thinking about how to change a DC signal (from 0 to X volts) into an AC signal (from (-X/2) to X/2 volts).

Instead of connecting the load between the DC signal and ground, I considered connecting the load between a DC signal and a second DC voltage (X/2).
If you read this section of your posts, there is no mention of a 'DC squarewave' only 'DC signal', which IMO means a DC voltage.?
 
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im_in_asia_now

New Member
I see what you're saying now.

What I'm talking about is changing a DC wave signal (DC square wave, DC triangle wave, DC sin wave, etc. oscillating between 0 and X volts)- with a shape and frequency- into an AC wave signal of identical shape and frequency (oscillating between -Y and +Y volts).

The way I would do this is by shifting the voltage of the signal. The schematic diagram I provided achieves this, changing a DC square wave from a 555 into an AC square wave with similar shape and identical frequency and phase.

I just wanted to see what other ways there are to achieve this, and how practical the idea was. Maybe I should try posting in general electronics chat since this isn't a big project though.
 
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smanches

New Member
It doesn't matter which forum you post in, except for general relevance. Most everyone reads all the forums anyway. This is why it is VERY discouraged to cross-post.
 
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ericgibbs

Well-Known Member
Most Helpful Member
I see what you're saying now.

What I'm talking about is changing a DC wave signal (DC square wave, DC triangle wave, DC sin wave, etc. oscillating between 0 and X volts)- with a shape and frequency- into an AC wave signal of identical shape and frequency (oscillating between -Y and +Y volts).

The way I would do this is by shifting the voltage of the signal. The schematic diagram I provided achieves this, changing a DC square wave from a 555 into an AC square wave with similar shape and identical frequency and phase.

I just wanted to see what other ways there are to achieve this, and how practical the idea was. Maybe I should try posting in general electronics chat since this isn't a big project though.
hi,
I have just run you circuit in LTS, where on the circuit are you taking the output from.?
 

shimniok

Member
One thought is -- it's just a question of what you consider 'ground' when measuring. Let's say you take a 0 to +12V signal generated by a 555 using just a +12V supply and feed it thru two identical resistors in series (voltage divider, IOW) Now, arbitrarily call the node between the two resistors the ground. Now you have a +6 to -6V square wave.

Otherwise, you'd need to find a way to convert a positive voltage into a positive and negative voltage. Like, alternately charge one of two capacitors from a +V source and turn around and use the caps to act as + and - voltage sources by whatever is consuming the power.

I ran across this recently and it seems that a great way to do this would be with a LM2663 - Switched Capacitor Voltage Converter

How to make that AC? Erm... use op amp signal generator(s) perhaps to generate square, sawtooth or sine waves... ?

Michael
 
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Hi gang,
Did anyone figure out how to do this? I have a project that needs this exact solution. I have a DC square wave signal 0 to 3.8v, varying frequency.
it needs to be converted to an AC signal for the device it's intended to drive; the device doesn't react to the DC signal. The final waveform could be square or sine...or triangle for that matter. Main thing is AC.

So, will the original method in the schematic using the 555 signal source work? (i don't have software to open the .asc file posted later).

thanks!

- a -
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Hi gang,
Did anyone figure out how to do this? I have a project that needs this exact solution. I have a DC square wave signal 0 to 3.8v, varying frequency.
it needs to be converted to an AC signal for the device it's intended to drive; the device doesn't react to the DC signal. The final waveform could be square or sine...or triangle for that matter. Main thing is AC.
As with the original poster, there's no such thing as a 'DC squarewave' - a squarewave is AC already.
 

BrownOut

Banned
Hi gang,
Did anyone figure out how to do this? I have a project that needs this exact solution. I have a DC square wave signal 0 to 3.8v, varying frequency.
it needs to be converted to an AC signal for the device it's intended to drive; the device doesn't react to the DC signal. The final waveform could be square or sine...or triangle for that matter. Main thing is AC.

So, will the original method in the schematic using the 555 signal source work? (i don't have software to open the .asc file posted later).

thanks!

- a -
Look at post #6. A simple capacitor does this for you.
 

MikeMl

Well-Known Member
Most Helpful Member
Why not just put a DC blocking capacitor in series with the signal, as shown here:
 

Attachments

As with the original poster, there's no such thing as a 'DC squarewave' - a squarewave is AC already.
I respectfully beg to differ. This signal is a square wave which oscillates between 0v and +3.8v.
An AC signal - Alternating Current - oscillates from 0v to some positive voltage, back to 0v, to some negative voltage, then back to 0v. F'rinstance, U.S. line voltage cycles from 0v to +110v, to 0v, to -110v sixty times every second; 60Hz AC.

What I am working with is a DC voltage that is simply being turned on and off very quickly, hence "DC square wave".
 
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