TMCM1290 EVAL phototransistor question

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Hello,

I’m using a TMCM-1290 evaluation board with a stepper motor and a phototransistor (GP1S093HCZ0F) for homing purposes. The board is connected via RS485 to USB.

The motor works perfectly, but I’m having trouble getting the sensor to interact with the motor. The sensor detects light at a single position, which should serve as the home position. Currently, the sensor itself works, but the motor does not respond when the sensor is activated.

The phototransistor is connected to the REF. SWITCHES input. I connected the cathode and emitter to GND, placed a resistor between the supply and the anode, and left the REF input connected to the collector. The board has a 4.7 kΩ pull-up resistor for the left REF input.

I tested by manually shorting LEFT REF to GND, which successfully triggered a logic low and caused the motor to respond to the TMCL code. However, this does not happen with the phototransistor connected.

Using a voltmeter, I measured 0.8 V between GND and the collector when light is detected, which the driver interprets as low, and 5 V when the light is off.

Any suggestions?

[jwet]

Look at how your ground current is flowing and where you are grounding the sensor's ground.  If it has appreciable ground current flowing in it, it could get elevated and the part won't see your .8v as a valid low.  A valid low is anything below 1v.

Also, the phototransistor is getting turned on but not very hard.  The collector voltage should saturate down below a quarter of a volt or so.  Decrease the resistor supplying current to the anode of the LED in your sensor to turn it on harder- don't exceed 20 mA or so.  You're getting .8v , this is close to 1v and with ground shifts could get corrupted.

Good Luck