A Schematic I'm trying to understand.

Martin_H

The schematic below contains a line following circuit on the left, but on the right it has a pair of signal conditioners for wheel encoders. The inputs are on sv3 and produce outputs on pins 9 and 10 of sv1.



These transistors look like inverters with a built in pull up to me. So absent any input or as an input rises above a critical threshold the output should be zero volts. As the encoder output falls to zero volts the transistor's base will be near zero, so the output will be five volts. So it seems to threshold the input to a digital output. But does it also provide any hysteresis to the output, or will glitches get passed through?

Phil Pilgrim (PhiPi)

Your take on the transistors is correct, and there is no hysteresis.

-Phil

Martin_H

Thanks Phil.

evanh

You could be getting issues around encoder power. I hope there is a resistor on each encoder output to limit it's draw. What value is R1? If R1 drops too much when driving Q1/Q2 then the encoder LEDs will go out.

I'd throw in a capacitor or two across the power rail also. Circuits feel naked without them.

Martin_H

@evanh, at the present time I'm only using the line following portion of the sensor. The wheel encoder portion is unpopulated, but if I do add the parts I would probably replace R1 with a zero ohm shunt and use a separate resistor for each wheel encoder LED.

Mark_T

The transistors may be to boost slew-rate as cheap-skate signal conditioning - 2 transistors cheaper than a 74HC14 perhaps?