Toggle button NE555 trigged over Arduino

Hi all, I realized in a pattern on the internet using a toggle button and ne555 monostable mode so everything is ok. Now, I’d like to add the ability to simulate pressing using digitalWrite from Arduino (which could be very useful in many situations), and I thought to use the classic means of a transistor (which should act as a switch) but it does not work, the circuit is closed but not ‘clicks’ as if it were closed by pressing the button. I am a neophyte electronics and certainly do not have the appropriate knowledge on the operation about ne555 to make arguments like this, the problem is probably due to the logic of charging and discharging of the capacitor, i have attached schematic. I noticed that every time I press the button, the polarity of the two ends of the button are reversed and so I added a diode to avoid a short, this system would be fine (if it worked) only when the polarity of the terminals A and B (indicated in the diagram) were respectively + and -, and not the opposite. On a site I noticed that they use a relay to do something like that but I would avoid this solution.

what do you think?

Happy New Year to all.


What are you trying to do?

Toggle on/off the Arduino using a momentarily-open push-button switch? AND also have the Arduino control powering on/off itself?

No I have explained myself badly. I would like to close the circuit in the schematic points A and B of the button, through a transistor triggered by a digital pin, I can do this, but it does not work the same as if it clicks the button pressed. I can not understand what to do.

What are you REALLY trying to do? (example: toggle lamp on/off with push button switch, fire death ray to moon, etc).

The reason for my question is maybe there's a simpler way to do what you're really trying to do.

i.e. Is there an absolute requirement that you must use this 555 circuit? (because you got the power of a microprocessor, why do ou still need a 555 ic chip?)

it is true, I would not need to do this using Arduino everything becomes easier, but I would like to avoid congesting Arduino as the project really needs to do too many things. Thought using a transistor to close this circuit was much simpler =(. thanks u vasquo and happy holidays.

You still didn’t answer vasquo’s question, and i’m having a hard time understandig your question and your goal.
Your schematic is also hard to read and what i can read doesn’t make any sense to me (but ofcoure that can be me).
But am i right to see you are trying to replace the button by the 2n2222 ?
The button has 3 contacts, P1, P2 and P3 and your transistor is across P2 and P3.
The button connects P1, P2 and P3 all together (strange, but that’s the way it is drawn).
And you just connect P2 and P3 with your transistor.
P1 is tied to the 555, P2 and P3 are not.
So any interaction between your transistor and your 555 is impossible.
So there’s your difference.

Do you really need to use this strange switch (why ?) or can you do this an other way ?

Hello and thank you for your interest. Put it this way: apart from the final goal, I want to close the points A and B with a transistor, simple. The terminals of the button are not all connected together, of course. In other terms, I want to replace the button with a transistor. I built this thing, but I do not get the desired result as if you had pressed the button.

I explained why you do not get the same result. If you press the button as shown (i'm not familiar with that symbol), then all inputs are tied together. Your transistor only connects A and B or P2 and P3. It does not break the connection between P1 and P2.

If the switch actually switches (toggles) P1 or P3 to P2 (so not pressed is P1 + P2 and pressed is P2 + P3), then you would need to also take over that breaker switch (P1 / P2). This can be done, you will need an extra transistor (different type) for that. I now see the title tells it's about a toggle switch, sorry about that.

Also, take in consideration that a transistor can be used as a switch, but it really is not a switch. You will have a larger voltage drop over this transistor as you would have over a switch. This might also contribute to an unwanted effect.

The schematic is unclear. Are you trying to blink (2) LEDs alternately using the 555 circuit? Then you want to turn on/off the 555 using the arduino?

What are you REALLY trying to do? It's a freaking simple question.

What are you REALLY trying to do? It’s a freaking simple question.

That’s apparently classified, :slight_smile:

ok, I simplified the schematic from the original design to the modified and running, try it if you have the components you will see that out pin3 is not activated.


Right. These schematics are readable. You are using the transistor as if it were a switch (that is your goal). You added a few diodes in the line between the charging capacitor and the threshold and trigger pins. This changes the way your 555 will operate, but doesn't per se kill it.

But where will the current go, needed for the transistor to work ? You'll have to figure out some other way to use your transistor to switch your blinker.

the transistor is working properly, but for some reason does not close the circuit as if it were a button press, I would like to understand this but I think I abandon the idea now

The transistor "generates" a voltage drop of about 0.7 volts, and so does the diode. (What's the reason for the presence of that diode ?) This is why i said you added a couple of diodes to the switch (a transistor can more or less be seen as a controllable diode). This effect allone will mess up your setup, and will show a difference between switching with a switch and with a transistor.

Just don't beleive what you're being told, measure and see what's going on.

If you want to be sure to replace the switch with something you can control with an Arduino or whatever, use that transistor to switch a relay.

the transistor is working properly, but for some reason does not close the circuit as if it were a button press, I would like to understand this but I think I abandon the idea now

Current needs to flow between Collector and Emitter of Transistor (controlled by the Base current) for it to work as a “switch”… so the “load” will be either in the collector or emitter leg. So the Collector terminal, through the “load” is connected to Vcc, and the Emitter to ground.

You just can’t substitute the Collector and Emitter legs of a transistor and treat it as the (2) physical terminals of a switch like the way you’d shown in your schematic.

Hi all. the transistor actually does its job without problems if the ouput of ne555 corresponds to high. each time you press the button, but the polarity (the collector and emitter terminals) therefore, the diode is used to prevent reverse current collector emitter circuit. Maybe then I can not explain, but if you have a way to do a test with the components you will realize the thing. Thank you all for your interest, I felt it was easier.