Square wave oscillator Off grid

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Jagau posted this 13 August 2020

Hi all
I would like to share with you this little square wave oscillator which works the same as a function generator and which operated on battery which can vary from 6, 9 or 12 volts DC according to your needs.


The heart of the oscillator is a TLC555 from the CMOS series which has very low power consumption and is completely different from the old NE555.

It has a 10K potentiometer to vary the frequency from 13Khz to 130Khz and another 5K potentiometer to increase the amplitude of the signal at will.

 

A drawing of the schematic that I present to you freehand


It can be easily changed by changing a single resistor and a single capacitor.

5 ma on 9 volts battery here


The particularity of this oscillator is that the output voltage changes from positive to negative through zero in the center. This is the AC square wave shape.

Most of these freely sold circuits are above zero volts they are only DC square wave and could not be use for experimentation.

Very low or high amplitude at your choice


This way you are isolated from the electrical network and have greater freedom of measurements without ground return.

 I also hope for those who would like to join us and experiment with us and do not have a function generator, this is the ideal opportunity, easy to assemble and inexpensive.

Jagau

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Chris posted this 13 August 2020

Hey Jagau,

This is awesome! A very nice, cheap project for anyone to take on that needs a small oscillator!

Thank You for Sharing! This is awesome!

Best wishes, stay safe and well My Friend,

   Chris

thaelin posted this 16 August 2020

Great addition to the group. Has a very tight transition time but then cmos is very fast usually. Big thanks and will add to the bench soon as can order the tl555.

thay

 

Jagau posted this 18 August 2020

Hello Thay


Yes the CMOS TLC555 has quite surprising performance especially when looking at the manufacturer's specs:

Minimum and maximum Rise time and fall time are very fast, they approach those of manufacturers of high quality function generators. These are very important parts when making oscillators.

I will be producing an addition to this oscillator shortly
to be continued

Jagau

Zanzal posted this 20 August 2020

Hello Jagau, the TLC555 is a very good choice. If you only need it to drive high impedance output like most gate drivers then it could be made significantly more efficient (likely less than 1ma at 10kHz).

Fighter posted this 21 October 2020

Hi Jagau,

As I found in specs TLC555CP (the version I found) is capable of going to about 2 MHz.

I tried to find a online calculator for resistors and capacitor to build one capable to go to 250 KHz maximum.

So far didn't found a useful calculator, the schemes for which they are calculating are different than your schema.

What values would you recommend to change for a version with 250 KHz maximum frequency (or maybe more, higher frequency is better) ?

For your schema how are these values calculated based on the desired frequency range ?

I intend to build one for a QLED experiment.

Thanks for help.

Jagau posted this 21 October 2020

Hello Fighter
When I built this oscillator I used the following formula:
In theory the generator's frequency can be calculated as follows:


f = 0.72 / (R1 * C1)


However in the reality the obtained frequency tends to be lower, especially at the higher end of the generator's range. This can be compensated for by adding a variable resistance rather than a fixed resistance.


I also kept some assembly notes to have different frequency ranges with a capacitor-resistor combination.
1 nF with 2.2 kOhm = 250 khz
1 nF 6.2 kOhm = 100khz
10 nF 2.2 kOhm = 30 khz
10 nF 6.2 kOhm = 10khz
0.1 uF 2.2 kOhm = 3.1 khz
A tip, it is best the best is to use a potentiometer to vary the frequency as desired.

So for your project change the 5k pot to a 2.2k pot. at pin 3 the other pot (10K) at output is for amplitude only

and pin 2 change 10nf to a 1 nf capacitor.

Hope this help

Jagau

Fighter posted this 21 October 2020

Sure, I intend to keep the variable resistors as in the schema.

So for a range up to 250 KHz it should be something like this ?

Jagau posted this 21 October 2020

Hi fighter

No it is the 5k pot you have to change for 2.2k 

So for your project change the 5k pot to a 2.2k pot. at pin 3 the other pot (10K) at output is for amplitude only

and pin 2 change 10nf to a 1 nf capacitor.

Jagau

Fighter posted this 21 October 2020

Oh, okay. So variable resistor 5K becomes 2.2K. And the 10nF capacitor becomes 1nF. Right ?

Jagau posted this 21 October 2020

Yes

Jagau

Fighter posted this 21 October 2020

Thanks for the help !

Fighter posted this 4 weeks ago

Hi Jagau,

I'm currently building the oscillator and I have two questions.

The first question is: what's the value of this capacitor ? The same 1 uF like others ?

And the second question is: according to the specs TLC555CP can provide directly about 100mA which I think is more than enough to drive the primary coil for QLED devices. Would be wise to use it this way or should I add a MOSFET on output so TLC555CP will command it for supplying the current for the primary coil ?

Thanks for your guidance.

Note: in my build I added a 2000 uF electrolytic capacitor on the input of the circuit for a later use, it shouldn't have any impact on the oscillator's functionality. I intend to try to use it later for charging it from the secondary coil (QLED-style).

Jagau posted this 4 weeks ago

 

Hi fighter


For the first question, the capacitor is a 0.1 uf or 100 nf


For the second, the manufacturer tells us that this integrated circuit allows you to easily make a 100 ma well with a 10 ma power supply within these limits if your leds do not exceed 100ma I do not think there is a problem.

According to this charter, you can even go up to 300ma but the IC will heat up,


Anyway, the output is fully compatible with cmos, ttl and mos, you can always increase your power.

For the 2000uf capacitor at the input, we normally use  between 1-100uf  with 0.1uf in parallel. The small capacitor is used to cut high frequencies which could degrade the use of the integrated circuit and the large capacitor for the low frequency line filtering.

I imagine you want to use it as a future power source instead of a battery?

Jagau

Fighter posted this 4 weeks ago

Hi fighter

For the first question, the capacitor is a 0.1 uf or 100 nf

Got it.

For the second, the manufacturer tells us that this integrated circuit allows you to easily make a 100 ma well with a 10 ma power supply within these limits if your leds do not exceed 100ma I do not think there is a problem.

According to this charter, you can even go up to 300ma but the IC will heat up,


Anyway, the output is fully compatible with cmos, ttl and mos, you can always increase your power.

I think I'll go without MOSFET for now.

For the 2000uf capacitor at the input, we normally use  between 1-100uf  with 0.1uf in parallel. The small capacitor is used to cut high frequencies which could degrade the use of the integrated circuit and the large capacitor for the low frequency line filtering.

I imagine you want to use it as a future power source instead of a battery?

Jagau

I also kept the small capacitor in place, the bigger one is additional.

That is correct, the bigger capacitor will be the power source in the future, that's the plan.

Thanks for the guidance !

Fighter posted this 3 weeks ago

This is my build of Jagau's AC Oscillator.

I know that in my build I pushed the frequency range to the limits.

You'll see I placed two sockets so the 10nF capacitor and the 5K variable resistor can be easily replaced with different values to change oscillator's frequency range (link to larger image here):

The only modification I made was to add a 2200uF/25V electrolytic capacitor on input.

In the following scope images I'm using a 9V battery on input, an 1nF capacitor and an 2.2K variable resistor which is offering a range starting at 266KHz and ending at 2.05MHz. The scope probes are connected directly on output and there is no other load.

Frequencies shown in the images are (in order): 266KHz, 510KHz, 833KHz, 1.25MHz, 1.76MHz and 2.05MHz.

You'll notice that as I'm forcing the frequency up the square wave is becoming deformed, my electronics knowledge is limited so I don't have a explanation for this but I suppose there is one and this is normal.

Also depending on frequency there seems to be a slight difference between the positive voltage (Max) and the negative voltage (Min), also don't know the cause for that (link to larger image here):

But we don't need MHz frequencies for our experiments so it's an excellent oscillator for experiments were real AC is needed even if we're using DC for input.

Just want to thank to Jagau for this excellent AC Oscillator, I intend to use it in QLED-type experiments.

Jagau posted this 3 weeks ago

Hello fighter
nice job, you now have one more tool in your lab, I often use it too.
A recommendation from the manufacturer is this in section 10.1;


10.1 Layout Guidelines
Standard PCB rules apply to routing the TLC555. The 0.1-μF ceramic capacitor in parallel with a 1-μF electrolytic
capacitor must be as close as possible to the TLC555. The capacitor used for the time delay must also be placed
as close to the discharge pin. A ground plane on the bottom layer can be used to provide better noise immunity
and signal integrity.

For the question of lowering the negative side you will have to make a power supply circuit with a virtual ground, this will correct the problem of voltage difference.
I recommend this simple and efficient one for all the ICs that you will have to use in the future.

This circuit is not mine, it works very well I use it in my setup

Jagau

 

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