Two semi-related questions regarding driving a 3 volt pager motor off a 9 volt battery. I'm planning on wiring everything up the same way as is done here (This NPN transistor controlled by the Arduino, with a capacitor and diode in parallel with the motor), but the voltage source is 9 volts and the motor is supposed to run off 3 volts. This leads to the following questions:
What is a simple way to get the motor to safely run? I was planning on adding resistors on either side of the motor to make a voltage divider so the motor receives ~3 volts (doesn't need to be perfect), but I want to make sure that'll be fine.
What type and what specifications should the diode be? 3v Zenner diode?
You could experiment with PWM to the transistor - this reduces the effective voltage
across the motor (well, actually the current), but the response probably isn't linear,
try analogWrite (pin, 85) ; to start with.
MarkT:
You could experiment with PWM to the transistor - this reduces the effective voltage
across the motor (well, actually the current), but the response probably isn't linear,
try analogWrite (pin, 85) ; to start with.
So as long as I keep the PWM signal fairly low, the voltage across the motor should be within acceptable limits as to not damage the motor?
This 143:1 gear motor spins at 40RPM at 3V, drawing 400mA at stall generating 44.4 in*oz torque (free running at 50mA).
If you set the PWM to 30% (75 .. 90 or MarkT'2 85 suggestion) and get max 40 RPM, I'd first check whether the tiny 2N3904 won't get too hot, rather than worry about the motor. ( 400 mA is way beyond the transistor's max Ic )
Ah, 2N3904 is limited to 0.2A, too low for motor! Choose a switching
transistor with 1A or more current rating, or a logic-level n-channel MOSFET
with a low enough Rds(on)
This 143:1 gear motor spins at 40RPM at 3V, drawing 400mA at stall generating 44.4 in*oz torque (free running at 50mA).
If you set the PWM to 30% (75 .. 90 or MarkT'2 85 suggestion) and get max 40 RPM, I'd first check whether the tiny 2N3904 won't get too hot, rather than worry about the motor. ( 400 mA is way beyond the transistor's max Ic )
Sorry, I should have provided a link to the actual motor I was planning on using - the one in the tutorial isn't the one I was planning on using, I was just planning on setting up the circuit that way. This (or something very similar) was what I was planning to use ( just need it to vibrate), and it's rated for 85 mA. Since the proposed transistor can handle up to 200 mA, I should be fine with pager motors as long as I don't get a crazy one right?