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square wave circuit

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Phasor

Member
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?
 

laroche73

New Member
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.

for some more info:

http://www.rez-gif.supelec.fr/~see/doc/logique/74C14.pdf
 

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townsvillian

New Member
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.
 

muki55

Member
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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vkssingh

New Member
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.
 

Hero999

Banned
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.
 

Styx

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

Comcat

New Member
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.
 

Hero999

Banned
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.
 

Comcat

New Member
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.
 

drivemusicnow

New Member
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?
 

Optikon

New Member
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.
 

drivemusicnow

New Member
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?
 

Optikon

New Member
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.
 

cortez47

New Member
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?
 

Mikebits

Well-Known Member
look up astable multivibrator.
 

cortez47

New Member
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.
 
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gudjoe

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