Mosfet project not working as expected

Ok I tried this on a breadboard and it worked. So much so that it burned my breadboard traces. So I moved it to a pcb but its not working. The source is a 7.4V battery and the nano is fed by a 5V battery pack. The mosfet is fqp30n06 but I put 2 jumper cables across the load and i get not voltage across it after 10 seconds that pin 5 goes high. The indicator LED that I also toggle whenever I set pin 5 to high or low works fine, it lights on and off every 10 seconds, but no voltage across the load. Here is my setup and my code:

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);

}

void loop() {
  delay(10000);
  Serial.println("burn!");
  digitalWrite(13,HIGH);
  digitalWrite(5,HIGH);

  delay(10000);
  Serial.println("off!");
  digitalWrite(5,LOW);
  digitalWrite(13,LOW);
  }

The diodes in the schematic appear to be backwards, but you say the LED works??? Are the two diodes supposed to be the load for the mosfet? Unless something else is missing and the diodes are actually wired the other way around then that would be a near-dead short across the battery when pin 5 goes high. Your sketch turns the mosfet off after 10 seconds. I would think both diodes would be toast.

I see numerous errors.

First off, You have the led reverse biased, with another diode in parallel. I can understand why the breadboard couldn't handle the heat if they were in the other direction. It would be a short circuit.

If the led is your load,

-get rid of the 1N4004

-put a current limiting resistor in series with a NEW led, (or ensure that one isn't burnt already). A 470ohm resistor will do, and put the cathode towards ground (Striped or marked end)

-the mosfet you have is not logic level. It needs 10V on the gate to be fully on. It might squeak enough current through to light the led, but it's not the right mosfet for use in the arduino. Look for one that has a RdsON voltage listed for 5V.

Connect the grounds together.

What is the value of R1?

Sorry, R1 is 6.2kΩ, the LED is not my load, its meant to be a dc motor and no, it doesnt work.

The diode's white band is connected to the 7.4V Vcc+ side.

So a motor sits where the led is. The diode is correct then. The biggest issues are the mosfet wanting 10V on the gate and not having the grounds from the 2 different supplies connected. The gate starts forming a channel when it reaches a certain threshold in relation to the source, listed as VgsTH. Without connecting grounds, the gate has no reference to the source. Just connect the battery - to gnd on the arduino

Connecting the grounds might make the motor spin like you want, but the mosfet will be dropping some of the voltage as heat. The motor might not spin as fast as it should. You really should find some logic level mosfets to play around with.

Hi, Have you got the gate,drain and source pins correct in the real world? Have you got the negative of the battery connected to the gnd of the Mega?

Can you please post a picture of your project and its PCB back and front?

Thanks.. Tom.. :)

Hi,
I think your are trying do do something like this;
Motor-MOSFET.jpg
The MOSFET is not a logic level device.
This is the pinout.
MOSFET_PINS.jpg
Tom… :slight_smile:

ok here is my pcb. Let me try to explain going down the board, top to bottom, right to left:

  1. The nano sits atop the female headers.
  2. The resistor goes out of GND (4th pin on the nano) right about the center of the pcb (6.2kΩ)
  3. Straight over to the left is a 2 pin female header where the 7.4V battery pack connects
  4. Just below the battery pins you can see the 3 pin female header for the mosfet GDS right to left
  5. Pin D5 on the nano goes out via red cable to the G of the mosfet
  6. The Drain of the mosfet connects via red cable to one pin of the motor and underneath to the diode
  7. The diode connects to the V+ of the battery headers
  8. The Source of the mosfet connects via black cable to the battery -

Sorry, I hadnt uploaded the right pic. The fuscia are the underneath connections...

Hi,

  1. The Drain of the mosfet connects via red cable to one pin of the motor and underneath to the diode
  2. The diode connects to the V+ of the battery headers

Please explain with a picture of your project please. What connections of the diode, cathode and anode, where do they connect?

Have you got the negative of the battery pack connected to the gnd of the Nano?

  1. The resistor goes out of GND (4th pin on the nano) right about the center of the pcb (6.2kΩ)

The resistor has two connections, where do they go? Please explain with a picture of your project please.

Thanks.. Tom... :)

Ah! Alas, the GNDS are not connected... ::)

Marciokoko: Ah! Alas, the GNDS are not connected... ::)

I'm pretty sure I mentioned that back in post 2. When asking for advice, listen to it carefully, then make the decision whether it is correct or not by investigating further.

Hi, And Post #6.

Tom... :o

Ok I connected the grounds, what Im doing is hooking up a voltmeter and measuring the voltage at the load connectors to see if there is a voltage diff after 10 seconds when pin 5 goes high to activate the mosfet. But nothing happens still.

Ok so Ill look for a ll mosfet...im trying to remember why I bought those fqp mosfets....

Marciokoko: Ok I connected the grounds, what Im doing is hooking up a voltmeter and [u]measuring the voltage at the load connectors[/u] to see if there is a voltage diff after 10 seconds when pin 5 goes high to activate the mosfet. But nothing happens still.

Have you got the motor connected? What is your motor, specs/data. Can you post a pic of your project with the motor and battery connected please? Thanks... Tom.. :)

Here it is...its a 3-9V motor. The battery pack is 2-3.7V in series so 7.4V:

I JUST NOTICED MY NANO IS UPSIDE DOWN!

I fixed it but I still get nothing. I checked my board for continuity at the points where I think there should be and its fine.

Ok I just tried out pin 5 by itself and I dont get 5V between D5 and GND. So D5 might have been ruined in my previous try when I burnt the traces on my bb.

Ok no, I just tried the nano directly on the pins D5 and GND and i get 4.78V on HIGH. So the board works.

I put the board back on the headers and Im measuring at the top notches of the GND and D5 pin while inserted into the headers and I dont get 5V, i barely get 0.01 at times. Im guessing something on the pcb wiring is responsible for that?

Ive checked the pcb and cant find anything wrong with it.

Hi, Remove the Nano from the board and with the DMM in Ohms or continuity mode check the board from pin5 to gnd. See if it indicates a short circuit.

Tom... :)

How about a picture of the BACK of the board

tinman13kup: How about a picture of the BACK of the board

See Post #8. Tom.. :)