Go Down

Topic: Project 9 related question (Read 10039 times) previous topic - next topic


I'm doing project 9 at the moment but it seems I have some gaps in my understanding that are bothering me enough to seek for some answers.

Could someone please explain how a diode does what it does.

If I connect motor to a LED and spin the motor manually the LED lits up momentarily. (Spinning magnetic poles result in induction induced back-voltage, that's fine.)
If I place a diode in series with the setup above the LED is either lit or not depending on which way the diode is placed. (Also fine, current only flows in one direction through a diode.)
If I place a diode in parallel with the setup above the LED is also either lit or not depending on which way the diode is placed. (This is where I start losing it.)
The same thing applies whether I put the diode before or after the LED.

So the diode not only prevents current from flowing through the component itself but also in the whole circuit. What is the mechanism?
Why can't the current just ignore the diode if it can't flow through it anyway.


By reading your story i question myself if you know that an LED is also a diode exept an LED lichts up and a normal diode dosent. The part where you discribe abou putting an LED and a diode paralel to eachother and the LED changes to on or off depanding on your diode, either means you dident place them parellel or you put the LED in wrong. diodes basicly conduct one way. Meaning if you put 5V on one end you get 5V out of the other, but if you turn it around you wont get anny voltage, same goes f.or an LED. I hope this information helps you abit, i coud go into more detail if you like, but my guess is that you dont need more detail.


Hi, I don't understood how the MOSFET work... I think that the MOSFET connect the source to the drain when a voltage is applied to the gate, is that true? Because I did some experiments with my MOSFET but it seems that the gate is always connected to the source and not to the drain, because the tester says there is continuity trought gate and source when on the gate there isn't any voltage applyed and where there is a voltage too soo gate and source are always connected but neither of the two is connected to the drain...
Sorry but it's my first time with a MOSFET and I can't understand it's working. :~ :~
And I'm sorry for the bad language too, I'm not english  :P
Thank in advance. Soon!


Jun 15, 2014, 03:47 am Last Edit: Jun 15, 2014, 05:04 am by Dansercoer Reason: 1
Why can't the current just ignore the diode if it can't flow through it anyway.

The current can, the voltage can't. But I also don't know why the diode is not in series with the motor to prevent back-current from damaging the transistor?


I am not able to get the MOFSET to activate by the DigitalOut Pin 9.  If I apply direct positive voltage to the lead, it works.

I have printed out the value of Digital out from pin 9 and it seems to be correct.  I have also applied power to the board by another 9 Volt battery thinking that my Raspberry PI is not supplying enough voltage to activate the MOFSET.

Is anyone else experiencing this?


Go Up