# Need to generate a 1kHz square wave with amplitude +12v to -12v

#### tonydix

Jul 29, 2021
5
The title says it all. Could use a 555 timer or an arduino which I have or could purchase an op amp but which one ? Miss typed kHz Sorry
Many thanks
Tony

[kHz ]

Last edited by a moderator:

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,805
[mod edit: corrected the title]

A 555 is a good choice for a 1 kHz square signal. An Arduino may be a tad more precise. It's up to you to decide the source depending on your requirements.
From there on you can easily amplify to +-12 V. Almost any opamp is suitable at 1 kHz. Other factors to consider are:
- required output current
- available supply voltages (If you have only +-12 V supply, you'll need a rail-to-rail opamp)

A square wave can also be amplified by a simple transistor based level shifter.

Have a look at this thread or this one.

Last edited:

#### tonydix

Jul 29, 2021
5
Thanks for the response. I can see many circuits which use the 555 for 0v to12v square wave but I dont see how they handle the -12v.
I was thinking of using an old pc power supply to deliver the +12v and -12v to the 555. Would I therefor need a dual 555 timer ?
Thanks

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,805
I dont see how they handle the -12v.
By amplifying and level-shifting the 0 V ... +12 V signal. You can use an opamp (used in an adder configuration) or see the links in my post #2.
Would I therefor need a dual 555 timer ?
That wouldn't help, both would work from 0 V ... +12 V only, still no -12 V output.

Moderator
Sep 5, 2009
14,304

#### tonydix

Jul 29, 2021
5
post-1696148 looks very interesting but I dont understand how vss and vdd are generated by the unit top right. Could you explain.
Thanks

#### tonydix

Jul 29, 2021
5
That looks very helpful would a 741 IC fit the bill ?
Thanks
Tony

#### WHONOES

May 20, 2017
1,217
The input impedance of the good old 741 is quite low, in the order of 100K if my memory serves me correctly, which would affect any calculations. I would go for something a bit more modern like the TL series of op amps ant of the TL031, 071, 081 would fit the bill. If all you have to hand is the 741 then it may be worth trying. The slew rate of the 741 is quite slow but if rapid rise and fall times are not required then that may not be an issue.

#### AnalogKid

Jun 10, 2015
2,927
How much output current do you need? What is the +/-12 V signal driving? Do you need a fast rise or fall time?

Depending on the answers, this might be done with a 2-transistor booster stage driven by the 555 output.

ak

#### tonydix

Jul 29, 2021
5
Thanks I was hoping for 250ma !

#### AnalogKid

Jun 10, 2015
2,927
Way to bury the lead. No "standard" opamp can supply anything near that voltage and current. A power opamp from Apex or Burr Brown can, but they are expensive. I have a circuit somewhere, from another thread.

ak

#### WHONOES

May 20, 2017
1,217
It is easy enough to put a couple of transistors on the output of the opamp to boost the current required.
I'll post a circuit in a while. I will include current limiting to protect the output against a short circuit.

#### WHONOES

May 20, 2017
1,217
See attached schematic and graph. The potentiometer has been included so that you can adjust the frequency to your exact requirements.

Any questions, come back!

#### Attachments

• OPAMP MULTIVIBRATOR.pdf
11.4 KB · Views: 15
• OPAMP MULTIVIBRATOR-graph.pdf
576.9 KB · Views: 12

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,805
Alternatively use the 555 as you are used to and add a level shifter plus amplifier to provide the reuired output current:

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