Momentary switch problem

[astroman01]

Hello everyone, I have only recently started learning about transistor electronics, I mostly did Arduino and ESP32 projects. I have designed a simple momentaty switch circuit that when you press the button, the circuit outputs 12V and when you press the button again, it outputs 0V. The power is supply is 12V 1000mA. I used the IRFZ44N mosfet and BC558A transistor. The capacitor is a 2.2uF tantalum cap. The resisor values show on the schematic. I have build the circuit on a breadboard. I think there may be a mistake somewhere, all the legs of the transistor and mosfet show 12v whether you push the button of the switch of not. I have attached the schematic and a photo of my breadboard circuit. The momentary switch has 4 channels and then the blue wire is the MASSE (which is ground). I have used the green wire as in this circuit which is channel 3. Any advice would be appreciated.

 

[KlausST]

Hi,

some questions / issues:
* on the bread board: are the top power bars connected with the bottom power bars?
* what´s the idea behind the BJT? How do you expect it to work?
* on the pictures with the bread board, I see a blue wire I expect it to be "GND" of the switches. But it is not connected to GND. At your schematic I see it should be connected to individual capacitors C1, C2 ... each with an individual R to OUTPUT_GND. But I don´t see how this could be possible. I neither see the capacitor connected to GND, nor the resistor connected to OUTPUT_GND. There is a resistor at the (wrong side of the) capacitor .. but seems to have both leads connected to the same column#11 - this can´t work.
* I don´t see the IRFZ44 center lead to be connected anywhere.
* I can´t see how the circuit should work like an ON - OFF switch at all.
* I can´t see how it relates to ARDUINO / ESP32 at all

the circuit outputs 12V and when you press the button again, it outputs 0V.

To be correct: 12V is continously present at the output. GND is switched by the MOSFET ... although I don´t understand how it is meant to do so.

Klaus

 

[astroman01]

Hi Klaus, thank you for your reply. I mentioned Arduino / ESP32 because that is all electronics I have done. I am beginning to learn transistor electronics.

The bottom power bars are for the 12v 1000mA input. The top ones are the output.

Yes the blue wire is switch ground connected to cap. The capacitor positive side is on the left. The ground of switch is connected to + side.

Can you perhaps draw a diagram to assist me?
The BJT is controls the 12 v supply to the mosfet. The collector pin is connected to gate of mosfet

 

[D.A.(Tony)Stewart]

The circuit schematic does not work and teaches you nothing about electronics.

But your jumps and resistors should be short and straight like the schematic.

It is supposed to be a divide by 2 Flip Flop using a pullup PNP and pull down Nch FET to output with the charged cap position to either trigger the PNP On or turn the Nch & PNP off depending on the drain voltage. But fails miserably.

 

[astroman01]

The circuit schematic does not work and teaches you nothing about electronics.

But your jumps and resistors should be short and straight like the schematic.

It is supposed to be a divide by 2 Flip Flop using a pullup PNP and pull down Nch FET to output with the charged cap position to either trigger the PNP On or turn the Nch & PNP off depending on the drain voltage. But fails miserably.

Hi Tony, I would still like to make the circuit work, could you perhaps assist me?

 

[D.A.(Tony)Stewart]

What are the 4 switches supposed to do?
What is your load?
What do you expect to learn if no one else can figure it out?
Cut resistor leads to stand up (short + long) or lay flat (short+short) and rewire it like the schematic with short orthogonal connections.
The layout should look neat and tight. AWG22 telephone wire works best, cut and stripped to different lengths. with 2to 3 mm stripped.

Show a link to the source of this circuit.

 

[astroman01]

The load is for in a led lights in a motorhome. The circuit is something I designed myself, or tried to. If the cicuit can supply 12v to the output when I press the switch and be off/0V when I press it again, I will be happy with it. Does not need to be anything complex. The circuit I designed as shown in photo, is made so that each switch channel has one of those circuits and the ground of the switch (the MASSE)

 

[KlausST]

Hi,

I was about to ask exactly the same as Tony just did.

***
If I had to design 4 DC channels (12V 1A) controlled by 4 pushbuttons simply ON/OFF ... I guess I´d use a simple microcontroller. (and 4 logic level MOSFETs)
It results in the lowest part count:
1 x microcntroller (internally clocked, internal pull ups on the ports),
1 x power supply capacitor,
1 x 3.3V supply or 5V supply (even a zener will work),
4 x MOSFETs ... maybe MOSFET protection.
That´s it. The benefit is that it is very flexible for options.(like a dedicated power up default state, debouncing, timing, timed power OFF...a nd so on)

***
But for sure a D-FF per channel, a JK-FF per channel .. would work too. But they need debouncing on each input.


Klaus

 

[FvM]

What's your trick to connect 4 switches with common ground to post #7 circuit that needs 4 isolated switches? Looks simply impossible.

 

[D.A.(Tony)Stewart]

I think the switches are irrelevant for the toggle power switch and used for Arduino purposes with internal pullup and debounce with 1nF across switches or in software.

the problem is R , hFE ratios to make the flip flop work. It does not as shown.

Can anyone make it work? The source link may have clues.

 

[BradtheRad]

Classic push-on-push-off switching circuit made from 2 NPN. Cousin of a bistable multivibrator. And both are cousins of the SR flip-flop made from 2 transistors.

Current flow through the capacitors is guided to turn on one transistor while shutting off the other. Adjustments are delicate in order to achieve a balanced condition that is easily pushed to imbalance. The long-tail pair characteristic assists snap-action.
Variations on this circuit can be seen via internet search.

Link below runs this circuit in Falstad's animated interactive simulator: (falstad.com/circuit)

tinyurl.com/ylw28amz

Click to navigate to website:
load schematic into simulator,
run it on your computer.

Select Toggle Full screen (under File menu)
Click the momentary switch to toggle the flip-flop (change state).