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# square wave circuit

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#### townsvillian

##### New Member
Hi I need a circuit diagram to make a square wave module for a project

Can anyone help me.

Thanks

There are hundreds of ways of generating square waves. Do you want a discrete component solution or IC? Variable frequency / duty cycle or fixed? What voltage? What frequency range?

simple square-wave generator

You'll probably get lots of 555 circuits here, but my favorite square-wave generator uses a single gate. You should use a high input impedance, CMOS schmitt-trigger input type like the 74HC14 (or 74HC132 if you want a gated oscillator). It's conceptually simple and works well. The oscillation period is ~ 1.7RC. The first cycle after power-up will be longer than the rest, because the cap has to charge to the STs upper switching threshold from ground. The duty cycle of this circuit is close to 50%, if you want an exact 50% duty cycle, run the oscillator at 2X the desired output frequency and follow it with a flip-flop.

Adding a couple steering diodes lets you vary the duty cycle by controlling the high and low periods independently.

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The voltage I require is 12v in and 24v 50Hz out.
It is to trigger solinoids which require 8VA each. I have up to 24 Solinoids but I expect that no more that 6 would be on at anyone time.

Try this !!!!!!!!

Its easy to make square wave with this software.
Just put your frequency and duty cycle you want and press calculate.

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Square wave from IC555

I am very new to Electronics, I need a circuit using IC555 with 3 sec ON and 1Sec OFF cycle square wave. The output has to drive a realy. The supply is 12V DC. The circuit should have flexibility to change the ON time using some switch or pot etc. Pls help. Most of the circuits I could find have fixed duty cycle and do not have any method to alter the duty cycle.

townsvillian said:
The voltage I require is 12v in and 24v 50Hz out.
It is to trigger solinoids which require 8VA each. I have up to 24 Solinoids but I expect that no more that 6 would be on at anyone time.
555 connected to an h-bridge with a 1:2 transformer on the output.

A 555 timer driving an h-bridge (though a buffer stage) being run from a 12V to 24V switching regulator.

for fixed freq (even fixed duty) I prefer a 74HC14-Schmitt with a resitive feedback and cap to GND

townsvillian said:
The voltage I require is 12v in and 24v 50Hz out.
It is to trigger solinoids which require 8VA each. I have up to 24 Solinoids but I expect that no more that 6 would be on at anyone time.

Do you happen to be in a country that uses a 50Hz mains voltage? If so, a comparator fed with a stepped down 50Hz sine wave can produce a 50 Hz square wave. It would be a very simple circuit and extremely frequency accurate. This approach is obviously useless if you do not have a 50Hz line voltage or if your circuit is not line powered at all.

If that's the case then I can't see why anyone would want a 50Hz squarewave over a 50Hz sinewave which can be easilly obtained from a transformer.

I do not know the purpose of his circuit and therefore do not know why he suggested that square wave is required. If a square wave is indeed necessary, then the approach I described will work given that he has 50Hz mains available. If a sine wave will suffice, then the solution is far more simple.

I need to create a square wave with a variable frequency. I originally tried to do this with a MC4558 op amp, however I ran into stability problems. Then I picked up a dual 555 timer and can't seem to get near the adjustment range I need.

Specs:

~10V input
Frequency range of between ~0-1200hz, linear response preferred
Needs to be stable, and protected from a signal failure.
Adjustable through the use of a potentiometer (we currently have 0-100k ohm pots)

Any ideas?

drivemusicnow said:
I need to create a square wave with a variable frequency. I originally tried to do this with a MC4558 op amp, however I ran into stability problems. Then I picked up a dual 555 timer and can't seem to get near the adjustment range I need.

Specs:

~10V input
Frequency range of between ~0-1200hz, linear response preferred
Needs to be stable, and protected from a signal failure.
Adjustable through the use of a potentiometer (we currently have 0-100k ohm pots)

Any ideas?

Getting down to 0Hz is going to be your problem. I would not do this with a 555. You can get great predictable response (linear) if you use a microcontroller to generate the waveform. You can get to true 0Hz this way.

True 0 hz isn't required. We are trying to create a fake speed sensor that at 0 Hz is 0 RPM, and is 16 pulses per rotation. Therefore really "close to 0" is all we need.

With the 555 we can only get an adjustment range between 115hz and 125hz (or a factor of that by using a different sized capacitor).

What microcontroller would you use and how would I set up the circuit?

drivemusicnow said:
True 0 hz isn't required. We are trying to create a fake speed sensor that at 0 Hz is 0 RPM, and is 16 pulses per rotation. Therefore really "close to 0" is all we need.

With the 555 we can only get an adjustment range between 115hz and 125hz (or a factor of that by using a different sized capacitor).

What microcontroller would you use and how would I set up the circuit?

Any uC with an A/D would do the job just fine. Set up a voltage divider with your external pot, run that into the A/D pin on a uC and then linearly map the A/D input voltage to your 0-1200Hz range. Then toggle an output pin at th eappropriate frequency.

Microchip has some low cost uC that contain A/D converter. There are many others as well (I'm not advocating Microchip)

If you can write a little C code to program the uC, this would be a low cost, fast way to do it. The hardware schematic is trivial.

Hello to everyone!

I need some help regarding a school project that's similar to the one discussed here:

I need to design a square wave generator with a variable frequency (2-5 kHz) , 50% duty cycle , but using only discrete components. What solution should I adopt?

look up astable multivibrator.

I know that's a posibility, but is it the best? Also, I need to be able to adjust the amplitude of the wave to 0-1 V (peak to peak) so could you offer me some suggestions about a simple amplifier that can do that?
I was thinking of projecting an audio-frequency oscillator and hook it up to a Schmitt trigger to form the square wave.

Last edited:
hi please am in need of as simple squarewave generator using few components.frequence of 2hz and workingvoltage of 3v

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