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Portable Low Frequency square wave generator circuit - Solved - page 3

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Laszlo:
Hi, as per zero 999 states, the 400mA current is rubbish. I don't know how I measured that with my calibrated DM.
The frequency output needs to be accurate to +-5% to simulate reasonably accurate speed.

I know it sounds absolutely dreadful, but I do need a circuit diagram of the whole thing as I have already tried to mesh a few things together with very little success (so far I killed 2 555 timers and my first lm741 had literrally burn't out once i plugged the positive end of the psu)

Do you think that the improved 555 timer desing which had been linked would be good enough for this? But again, how would I ac-couple the output of that, and how could I make that adjustable so it would keep its duty cycle?

rhb:
I'd like to suggest you consider an MSP430G2 LaunchPad with Mecrisp forth loaded on it driving a suitable solid state switch.  Super simple to program if you follow the PWM  example in the README.  Cheap too.

Zero999:

--- Quote from: Laszlo on January 27, 2019, 10:59:08 pm ---Hi, as per zero 999 states, the 400mA current is rubbish. I don't know how I measured that with my calibrated DM.
The frequency output needs to be accurate to +-5% to simulate reasonably accurate speed.

I know it sounds absolutely dreadful, but I do need a circuit diagram of the whole thing as I have already tried to mesh a few things together with very little success (so far I killed 2 555 timers and my first lm741 had literrally burn't out once i plugged the positive end of the psu)

Do you think that the improved 555 timer desing which had been linked would be good enough for this? But again, how would I ac-couple the output of that, and how could I make that adjustable so it would keep its duty cycle?

--- End quote ---
I agree, you need a complete schematic. You can stitch one together, once you have all of the building blocks in place.

The problem with the 555 timer is it's difficult to get a 50% duty cycle output. Your best bet is a CMOS variant, such as the 7555.

Another option is an astable with a divider to give a square wave. See attached for an example using the 4013 to 74HC74. The potentiometer sets the frequency and the switch changes ranges. I suggest you have at least two, say 1Hz to 30Hz and 30Hz to 1kHz, is getting 1Hz to 1kHz with one setting will be tricky.

This schematic isn't quite complete, hence the lack of component designators. You'll probably need to alter the component values.

spec:
HI Laszlo,

Attached is a schematic for a pulse generator to meet your requirements:

It is intended to be powered by a couple of mains to 12V, 1A or more, stabilized power supplies, which are available from many sources at quite a low price. Battery power could also be provided, if required.

The frequency control is by a single potentiometer to sweep from below 1Hz to above 1kHz.

Note that the 555 timer is a CMOS type- an ordinary 555 will not do.

http://www.ti.com/lit/ds/symlink/lmc555.pdf

http://www.ti.com/lit/ds/symlink/ucc21520.pdf

https://www.onsemi.com/pub/Collateral/FDD3672-D.pdf

https://www.onsemi.com/pub/Collateral/FDD3682-D.pdf

soldar:

--- Quote from: Zero999 on January 27, 2019, 11:50:03 pm --- The problem with the 555 timer is it's difficult to get a 50% duty cycle output.
--- End quote ---
There are several circuit designs with 555 timer that allow anywhere from 0% to 100% duty (with logical limits at both ends of the range) and there is no problem getting 50% duty cycle. OTOH it is easy to start with double the frequency and then divide by 2 and this results in 50% duty cycle exactly always and every time.

This project seems like it could be done very simply with a 555 timer, powered with 6+6 volt split supply or with a single supply and decouple the output with a large capacitor. Insert 50 ohm resistor in line with output and that should cover it.

Depending on where you are going to connect this device you might want to isolate it well, very well or really, really well.

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