hi,
It is only a simulation of his circuit, to show the operation, it is not optimized.
Of course I expect him to make any required changes.

 

hi,
Look at this, 3.6kHz tone while the switch is closed.
Simplified version of your circuit.
E
Update MOSFET .

Try a FDS4072N3

Thanks

Indeed as adviced the N MOSFET is the suited one

1. As crutschow asked why do you propose a lower value for R2?
2. And why do you use C3 with 47uF?

Thanks for the advices and help

 

hi G,
I am not proposing a low value resistor, it is a simple simulation of a MOSFET switch.

When using a voltage regulator you must use decoupling capacitors.
Your circuit has no values for the components or the value of Vcc

The simulated circuit will not give you a 1sec On/Off of a 3kHz signal.

Are you asking for a design of fully working circuit.??

If so please specify which type of MOSFET you have available and the 9V reg type, value of Vcc etc...

E

 

hi G,
I am not proposing a low value resistor, it is a simple simulation of a MOSFET switch.

When using a voltage regulator you must use decoupling capacitors.
Your circuit has no values for the components or the value of Vcc

The simulated circuit will not give you a 1sec On/Off of a 3kHz signal.

Are you asking for a design of fully working circuit.??

If so please specify which type of MOSFET you have available and the 9V reg type, value of Vcc etc...

E

Ok thank you, I understand now. I thought you proposed those values for that reason

I didnt know it was for decoupling. I usually place 100nF and another of 1uF normally close each IC as decoupling. I asked about the capacitor because I didnt know if it was recommended when using a the MOSFET as a switch, as I wasnt familiar with the MOSFET application.

Im not trying anyone to give me a fully working circuit to anyone. I am trying to learn something else before buying some parts and start doing some tests. I will be using an external AC-DC 12 or 24V converter or in case I can run an electrical line maybe I use a 12 or 24V large battery.
- As voltage regulator I think I will use standard L7809
- As N-MOSFET, I would choose something else from the adviced because it seems to be obsolote and because it is I think too big. DMN3018SSS could be a good option I think

 

I want to use a NO switch, so using a NC switch is not an option.

It would help *greatly* if you posted the schematic in your head; without it, this is a guess. You can do this with the NO switch and one resistor.

1. The Reset input (pin 4) probably is connected to Vcc. Disconnect it. If it is connected to Vcc through a resistor, what is that value?

2. Connect Reset to Vcc through a medium-value resistor (10 K - 47 K).

3. Connect the switch between the Reset input and GND.

When the magnet approaches the circuit, the switch closes and holds the 555 in the Reset state - output low, timing capacitor held close to GND.

ak

 

hi G,
The DMN3018SSS N MOSFET looks suitable, bit over rated in Drain current, what price are you paying.?

Do you still want a 1Sec On/Off rate of a 3.5kHz square wave drive for the piezo.?
Have you considered a 9v audio beeper instead of the piezo, it would cut the need of a second 555.

E

 

hi G,
The DMN3018SSS N MOSFET looks suitable, bit over rated in Drain current, what price are you paying.?

Do you still want a 1Sec On/Off rate of a 3.5kHz square wave drive for the piezo.?
Have you considered a 9v audio beeper instead of the piezo, it would cut the need of a second 555.

E

Unit price for the N MOSFET is 32cents. There are other SOT23 with smaller package that can drain around 0,5A

1Sec On/Off rate of a 3.5kHz is not strictly neccesary. It was an example just to say that I didnt want a nonstop sound. I think that achieving a 50% duty cicle would produce sound intermittently and without the need of an extra 555; even if the intervals are shorter than 1sec

 

I think that achieving a 50% duty cicle would produce sound intermittently and without the need of an extra 555; even if the intervals are shorter than 1sec

hi G.
How would you achieve a 50/50 cycle rate that was suitable to drive a piezo, that would produce sound intermittently, that you could hear.??

Post a sketch of your idea.

E
BTW: which type of piezo do you have.?

 

I was reading that adjusting the capacitor and resistor values it could be possible to achieve 50% duty cycle

I will need to change the voltage regulator because the thin piezo work at 3V-5V. I will pick a switching 5VDC fixed output voltage regulator.

As piezo I think this could be suitable for me as it has 3mmthickness
https://www.cuidevices.com/product/resource/cpt-1203-78-smt-tr.pdf

 

hi G,
The piezo you posted requires a 4kHz square wave drive, of course you can set the 555 to give a 50:50 drive, but it will sound continuously while the 9V is applied.
ie: while the switch is Closed.
Is that OK.?

Look at the Vppk to Drive.!

E

 

You can also use a CMOS inverter as an oscillator and then the other gates as an amplifier to drive the piezo device and have less standby current, and only need one capacitor. and then the switch can just stop the oscillation and so the total current draw will be very small. This idea just hit me while eating breakfast.

 

hi G,
The piezo you posted requires a 4kHz square wave drive, of course you can set the 555 to give a 50:50 drive, but it will sound continuously while the 9V is applied.
ie: while the switch is Closed.
Is that OK.?

Look at the Vppk to Drive.!

E
View attachment 217223

Ok, it can take the 9V

It is a bit more disturbing to have the whole time the sound but I think it would be smaller the circuit just using one 555

You can also use a CMOS inverter as an oscillator and then the other gates as an amplifier to drive the piezo device and have less standby current, and only need one capacitor. and then the switch can just stop the oscillation and so the total current draw will be very small. This idea just hit me while eating breakfast.

How would you do that? I truly dont know. I really thought that the easiest way to drive the buzzer was using the 555 as oscillator

 

With this calculator I could set the values to obtain a 4khz frequency

 

This is another option and it doesnt use R1. It also has a 50% duty cycle

 

The minimum value for R1 is about 1kΩ, it can't be zero.

 

hi G,
This is your circuit in LTS, note the two 1k2
Looks OK at ~4kHz, not 50:50
E

I was using post #53.!

 

hi G,
Look at this option for 50:50.
E

 

hi G,
Look at this option for 50:50.
E

That will give 50:50 with an idealized 555 (or a CMOS 555) with output equal to the supply.
A real 555 will have an output about a diode drop below the supply, and thus the duty-cycle will be slightly off from 50:50.
Use the 555-1 model, if you have it.

 

Ok, it can take the 9V

It is a bit more disturbing to have the whole time the sound but I think it would be smaller the circuit just using one 555
One CMOD inverter as a


How would you do that? I truly dont know. I really thought that the easiest way to drive the buzzer was using the 555 as oscillator an oscillator, with a capacitor to common and a resisttor for feedback, followed by another inverter driving two in parallel, while the oscillator output direct drives the other two inverters for the opposite phase. The piezo element connects betrween the outputs of the two sets of two inverters. The closed switch keeps the input ogf that oscillator held low, and none of the gates are outputting any current until oscillation starts. One resistor, one capacitor, and one 4049 hex inverter IC. That is about as simple as I can make it. And the piezo will be rather lioud with 2x Vcc as rge drive voltage;

 

Hello everyone,

I have a circuit regulated with a LDO 9VDC that uses a 555 timer and I want it to work when I activate the circuit with a magnet. Willing to do that I chose a reed switch and as I could read, most reed switches have a NO contact.

That said, the normal application would make the 555 work when you approach a magnet to the switch and the contact is closed; but I want to reverse it, I want to make the 555 timer work when the magnet is far from the swtich and stop working when the magnet gets close and the switch closes.

What do you think is the most efficient way to do this? I want to use a NO switch, so using a NC switch is not an option.

Did you consider MrBill2 suggestion in post #59?

You wouldn't need a 555. Setup the a NAND as a "gated" oscillator so it can be enabled or disabled. The duty cycle will be near 50%.
Use a CD4093B Quad Nand gate, it can also be used for debouncing the switch and can run at 9v. Use a mosfet to drive the piezo.