I'm using 4 Si2302 logic level mosfets to drive 4 coreless dc motors. The speed of the motors is control led by the PWM signal from an Arduino Pro Mini. The power supply for the boards is a 3.7V (4.2V when fully-charged) 500mAh 50C Lipo.
The circuit is setup in the following way:
- Source to ground
- Gate to PWM pin with a 10KΩ resistor to ground.
- Drain to motor terminal 1
- Motor terminal 2 to Vcc
- Diode placed across the motor terminals
The motor gets its RPM value via a joystick which is connected to an Analog Input on the Arduiuno. This is then converted to a 0-255 value and outputted at the PWM output.
I'm facing the following problems with the circuit:
As soon as I supply power to the circuit the Motors run at full RPM till the Arduino starts taking data from the joystick. It then settles down to the RPM corresponding to the joystick position. Is there any way to counter this so that the motors remain switched off until the Arduino starts receiving values from the joystick ? (My understanding was that the 10KΩ Rgs resistor would take care of this.)
The second problem is that the mosfet never fully switches off. This happens even when the joystick is at the 0 position. I have also tried switching the pins HIGH and LOW, however there is still movement in the motor. Is there any remedy to this problem?
When I measure the resistance between Gate and Source, the mosfet shows around 6K ohms. Shouldn't this be around 10KΩ since the Rgs resistor is 10KΩ ? Is this a sign that the mosfet is damaged ?