Resistors value help

willy1067

I modified a IBM parallel circuit to work with the basic stamp 2.

I am using motors that require more power consumption than the original circuit provides, so I will change Q1-Q8 from MPSA13, NPN to larger IRF510.·· Now by doing so I will need to change the value of resistor R18 from 1k ohm to what? (I think 2 ohms) due to my motor M1 changing from (150 ohms resistance, 180 mA current, 4.86 W/m power)· to (31 ohm resistance, 610 mA current, 12 W/m·power).

Also, because each new motor consumes 610 mA of current each, and the IR510 able to drive 4 Amps, I figure that I can only drive·4 motors at a time·without heating sinking protection.· (Am I right?)

Also, The ground in both the BS2 and the separate power supply are joint.
Is this safe for the BS2?

Post Edited (willy1067) : 12/8/2007 11:41:47 PM GMT

Mike Green

The IRF510 is not designed to switch using logic levels. You want the IRL510. If you use the IRF510, it may turn on, but not supply adequate current to the motor. Look at the datasheet for the MOSFET. You'll see graphs of gate voltage vs. drain current. You may see that the drain current is not high enough for the motor when 5V is applied to the gate.

R1 through R8 are not necessary with the MOSFET. You would want some kind of resistor between the gates and ground to hold off the MOSFETs when the Stamp is reset and the I/O pins are set to INPUTs, but the LEDs and their resistors will do the job.

The ground for the BS2 and the whole motor circuit has to be connected together. Just do the wiring so that the high motor currents don't flow through the wire to the BS2.

The LM317 regulator will not be able to handle the current for all the motors. Can you run the motors directly off the 6-9V input?

Mike Green

1) Don't use R1-R8. Just eliminate them.

2) There's a different symbol for MOSFETs. Look at the first page of the datasheet for this: www.ortodoxism.ro/datasheets/irf/irl510.pdf