Hi,
I've been building a test/proto perfboard for game buttons. Concept is simple: 4 'action' buttons, 1 reset button, a buzzer and some indicator LEDs.
The original design is (src:elonics.org):

The modifications I made is replacing the LED+resistor on the 555 output with an IRLZ44N connected with gate to the 555 timer output to turn on a piece of 24V LED strip, and made it a 4 button circuit.
Reason for this is that the circuit is powered by 12V (VCC in next drawing) and the LED trip runs on 24V.
So the 'new' design is:

So I put everything together:


So, left photo: top bar and middle 'bar' are negative.
Right photo: bottom line is VCC (12V). Brown is negative rail, blue is reset rail and green is the status rail.
Soldering wise it was easier to connect all 24V's going to the buttons in a cluster near the first (right one, on the 2nd photo) 555 timer, so I did.
This all works though due to some weird issue with the first button (right on 2nd photo) that when one other button is pressed, eventually the led strip connected to the first (right) 555 timer suddenly started to turn on slowly. Even when the 555 timer was removed.
While trying to find out the cause, I'd read somewhere that between Gate and Source, a MOSFET acts as a capacitor. This in my opinion explains the slowly powering on of the MOSFET/ledstrip. So I placed a 10k resistor between the trigger pin and ground.
This helped as the first button doesn't turn slow on anymore when another button is pressed. BTW: only the first555 timer MOSFET slowly turns on, the others just work as expected. I can't measure the voltage rise on the gate because as soon as I either connect my multimeter or oscilloscope, it turns off. Which also made me think of adding the pull-down resistor.
So my question is why is this happening? Why is that single MOSFET turning on by itself?
Is it because I placed all 24V+ lines near it? And is the first MOSFET 'charging' due to inductance? Should I add pull down resistors to the other MOSFET gates as well?
I did triple check all traces/connections and there are no bridges etc that shouldn't be there.
any thoughts are welcome.
[edit]
Edit's to complete initial post based on additional questions in comments.
* IC has been swapped, 'issue' stays with the same 'position'. To add to this, I've also replaced the FET and the diode.
* with the connected pull-down the led strip does turn on when the button is pressed.
KR,
Onno.
I've been building a test/proto perfboard for game buttons. Concept is simple: 4 'action' buttons, 1 reset button, a buzzer and some indicator LEDs.
The original design is (src:elonics.org):

The modifications I made is replacing the LED+resistor on the 555 output with an IRLZ44N connected with gate to the 555 timer output to turn on a piece of 24V LED strip, and made it a 4 button circuit.
Reason for this is that the circuit is powered by 12V (VCC in next drawing) and the LED trip runs on 24V.
So the 'new' design is:

So I put everything together:


So, left photo: top bar and middle 'bar' are negative.
Right photo: bottom line is VCC (12V). Brown is negative rail, blue is reset rail and green is the status rail.
Soldering wise it was easier to connect all 24V's going to the buttons in a cluster near the first (right one, on the 2nd photo) 555 timer, so I did.
This all works though due to some weird issue with the first button (right on 2nd photo) that when one other button is pressed, eventually the led strip connected to the first (right) 555 timer suddenly started to turn on slowly. Even when the 555 timer was removed.
While trying to find out the cause, I'd read somewhere that between Gate and Source, a MOSFET acts as a capacitor. This in my opinion explains the slowly powering on of the MOSFET/ledstrip. So I placed a 10k resistor between the trigger pin and ground.
This helped as the first button doesn't turn slow on anymore when another button is pressed. BTW: only the first
So my question is why is this happening? Why is that single MOSFET turning on by itself?
Is it because I placed all 24V+ lines near it? And is the first MOSFET 'charging' due to inductance? Should I add pull down resistors to the other MOSFET gates as well?
I did triple check all traces/connections and there are no bridges etc that shouldn't be there.
any thoughts are welcome.
[edit]
Edit's to complete initial post based on additional questions in comments.
* IC has been swapped, 'issue' stays with the same 'position'. To add to this, I've also replaced the FET and the diode.
* with the connected pull-down the led strip does turn on when the button is pressed.
KR,
Onno.
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