hi,
The internal capacitance of MOSFET is very low.
You could try this experiment.

Remove the 1k from PIR to Gate and replace it with a signal diode in series with 100R.
Then from the Gate to 0v add a 1uF capacitor and a 1meg Ohm resistor in Parallel.

The 2 second On time should charge the 1uF cap , so that it holds a charge, the charge will then leak away through the 1meg Ohm.
See how long the LED stays lit.
If it is too short try a 10uF

Do you follow OK.?
E

 

I think I do yes.

But, if I replace the 1K at the gate with a wire and connect the wire (gate) shortly to vcc, then the mosfet will stay on and will not turn off until I connect the wire (gate) to 0v.

Thats what I have learned it should do from poul:

So what I wonder is, why doesnt it act the same way when PIR is connected to gate?

 

hi,
The only reason the LED stays On is because the way you describe it, means the Gate is 'floating' , ie: open circuit, until you connect it to 0V, then the Gate cap will discharge.

With the circuit you have on the bread board, the only way you can have have a longer on time is to charge that 1uF or 10uF.
E

 

So what I understand is that the PIR somehow discharges the mosfet cap.

You wrote that I had wired the BC transistor incorrect. How is that?

 

So what I understand is that the PIR somehow discharges the mosfet cap..... Yes

Prepare and post a drawing of the BC547 circuit section, then I can explain any errors.

 

thank you very much for your help, i really appreciate it.
I will look at it again tomorrow, im totally wasted

 

Sorry I dont know how to draw a circuit.
The first photo should give you the type number of the mosfet.

thank you

I’m not picking on you, but if you want to make electronic circuits, you need to learn how to draw them. Particularly when you need assistance.

Schematics (drawn electronic circuits) are the language of electronics. Without them, you cannot tell if you’ve hooked everything up correctly. And when you request help, your potential helpers can’t necessarily understand what you’ve done.

I’m sure that the pictures you posted seem to show everything, but perhaps a connection is hidden behind a component. Or two components that should be connected are plugged into different rows.

Since you searched and learned how to connect your components, I urge you to search and learn how to draw a schematic. The first skill helped you in this project. The latter skill will help you in all of your projects.

Just my two cents...

 

I’m not picking on you, but if you want to make electronic circuits, you need to learn how to draw them. Particularly when you need assistance.

Schematics (drawn electronic circuits) are the language of electronics. Without them, you cannot tell if you’ve hooked everything up correctly. And when you request help, your potential helpers can’t necessarily understand what you’ve done.

I’m sure that the pictures you posted seem to show everything, but perhaps a connection is hidden behind a component. Or two components that should be connected are plugged into different rows.

Since you searched and learned how to connect your components, I urge you to search and learn how to draw a schematic. The first skill helped you in this project. The latter skill will help you in all of your projects.

Just my two cents...

yes I am totally with you! thank you.

 

hi,
How long do you want it to stay On.?

Look at this link, you will find it useful for your projects.
http://fritzing.org/download/

E

I have downloaded Fritzing. I already need a part (PIR) so I have to draw a new one.
Ill try to look at some other programs that might have more parts.

 

I have downloaded Fritzing. I already need a part (PIR) so I have to draw a new one.
Ill try to look at some other programs that might have more parts.

“Fritzing” is terrible for communicating. It has many of the same problems as taking a picture.

CMartinez suggested ExpressSCH from ExpressPCB. I agree with his suggestion.

You can easily make your own parts with ExpresSCH.

 

sorry, expressshc wont work for me because they start asking for my email.
Im not fond of handing out my email address for them to having it laying around in all kinds of databases.