Hi All,

I would appreciate feedback on the proposed circuit for providing the limit switch input to a CoTS motor controller.

Switching Signal should switch high/low when the beam on the KRB031 is either interrupted or not interrupted.

Switching signal will connect to the IN3/LSN signal line of the motor controller.

The input on the motor controller is pulled upto 5V internally. This is why the circuit shown has no pull up itself.

R1 is set @ 220r to give 18mA current on the internal LED which is less than the 25mA max but should provide sufficient illumination.

The motor driver input requires minimum of 3.5V for logic high and maximum 1.6V for logic low.

Have I overlooked anything in the schematic?

 

R1 is set @ 220r to give 18mA current on the internal LED which is less than the 25mA max but should provide sufficient illumination.

I would set R1 at 390 ohm and R2 at 10K.
I don't think you need that much current through the LED.

 

Before all else I would suggest using a Logic Level MOSFET. Next in addition to sghioto's fine suggestion I would suggest a 10 K resistor to ground from MOSFET Gate to Ground.

Ron

 

Before all else I would suggest using a Logic Level MOSFET. Next in addition to sghioto's fine suggestion I would suggest a 10 K resistor to ground from MOSFET Gate to Ground.

Ron

The BSS138 should be fine:

Gate resistor to ground is OK but should be at least 10X the value of R2.

 

Appreciate that.

Ron

 

thanks folks very helpful.

Would you expect the output to switch almost entirely from 0v to 5V?

 

thanks folks very helpful.

Would you expect the output to switch almost entirely from 0v to 5V?

Yes.