Motor Stopping and Starting?

Hello guys,

I am currently trying to run a motor off a programmed chip (PICAXE 08M) by using an N-Channel Enhancement MOSFET (2N7000). Without connecting the output of the chip to the MOSFET it works fine (the LED on my testbed is ON). After I connect the Output of the chip to the gate of the MOSFET the motor turns on as expected, but then after a few seconds it will just turn OFF. Another few seconds it turns ON.

I can't figure out why this happens. If I just connect it to the LED again it's ON without any problems (as expected)

Any idea's why this is happening? Is it maybe noise?

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The Circuit is attached. Note that the BJT should be taken as an Enhancement N-Channel MOSFET as described above.

The data sheet for the motor is found:

**broken link removed**

The data sheet for the 08M PICAXE is attached.

If you don't have any decoupling capacitors on the power then it's likely noise from the motor is causing a problem. You should have a minimum of a couple hundred microfarad across the supply line and a 0.1µF cap directly across the PICAXE pins.

crutschow said:

If you don't have any decoupling capacitors on the power then it's likely noise from the motor is causing a problem. You should have a minimum of a couple hundred microfarad across the supply line and a 0.1µF cap directly across the PICAXE pins.

Click to expand...

Ahh.... Yeah I thought it might be that (worked better after I did put decoupling caps on it) so its not my actual design or anything obvious like that is it?

fouadalnoor said:

Ahh.... Yeah I thought it might be that (worked better after I did put decoupling caps on it) so its not my actual design or anything obvious like that is it?

Click to expand...

Nothing obvious.

Those little high rpm motors often have a lot of brush noise. You can suppress it by adding a .01 ufd across the motor and a .01 ufd from each motor lead to the metal case. It often helps to use twisted pair for the motor leads and the power supply as well.
The 2N7000 is not a logic level FET so it may have a little problem being driven from the pic. There is a logic level version of it but I can't recall the number off the top of my head.