Hi All,
I'm trying to figure out how Roomba dirt detect circuit works but having trouble to understand how the final stage works. I've drown a schematic from the pcb and did some measurements with an oscilloscope while tapping on the piezo sensor.
As far as I understand IN+ is a reference voltage. When IN- becomes greater than IN+ OUT drops low and pulls IN+ low through diode D4. This is some sort of hysteresis to implement output latching.
What I don't understand is how OUT stays 1.7V in idle state when IN+ is 2V and IN- is 0V. I believe the output should go to VCC which is 14V but my measurement shows it is 1.7V in idle.
I double checked the pcb and it seems like D4 is the only feedback from the OUT.
I would appreciate any help.
I'm trying to figure out how Roomba dirt detect circuit works but having trouble to understand how the final stage works. I've drown a schematic from the pcb and did some measurements with an oscilloscope while tapping on the piezo sensor.
As far as I understand IN+ is a reference voltage. When IN- becomes greater than IN+ OUT drops low and pulls IN+ low through diode D4. This is some sort of hysteresis to implement output latching.
What I don't understand is how OUT stays 1.7V in idle state when IN+ is 2V and IN- is 0V. I believe the output should go to VCC which is 14V but my measurement shows it is 1.7V in idle.
I double checked the pcb and it seems like D4 is the only feedback from the OUT.
I would appreciate any help.