Single ended spindle encoder (5i25+7i76)

Well, I have it wired this way currently, but still no success. Diodes did not die this time, however, so that points the problem elsewhere now.

Regarding the pull-up resistor, doesn't the 7i76 have internal pull-ups for all inputs? The current scheme is;

+5vp to to the + of phototransistor 1, 170 Ohm resistor to the + of the diode, in series to the next diode and to ground, the same +5vp in parallel to the + of phototransistor 2 and the - of both phototransistors to Encoder A+ and Encoder IDX+.

I'm seeing most phototransistors being hooked up differently though, so perhaps I'm doing it wrong. Should the negative of the phototransistor go to both ground AND the encoder input?

I'm using 12v for the field voltage and the cable is grounded, short cable. I'm not super worried about noise for now.

Thank you for your time.

Sorry, I forgot that the encoder input is 5V. Ignore that suggestion.

Can you see a voltage change at the 7i76 input pin when you move the disc through the sensor?

No, I cannot. I'm thinking the phototransistor must be improperly wired, as now with the resistors the diodes ought to work just fine (Unless wiring them in series causes some issues, but I don't see how, it's no different from two LEDs). Both diodes still respond to a diode tester on a multimeter.

I have two thoughts currently:

1: Should the phototransistor + side go to both ENC + and ground?

2: Am I wrong connecting +5VP to the + of the phototransistor and into ENC +, alternatively being ENC + into phototransistor + and the phototransistor - to ground?

Chibs wrote: 2: Am I wrong connecting +5VP to the + of the phototransistor and into ENC +

Yes, because that means that the ENC+ is always +5V
You need a resistor such that the phototransistor can pull the voltage down to < 2V with only 10mA or so of current.

What I mean is it's 5VP to the + of phototransistor and the - of the phototransistor to ENC +, sorry if I wrote it confusingly.

I think my thought process was that the phototransistor would not conduct at all when blocked, but I'm now understanding it simply changes resistance.

I'm afraid I don't fully understand how to wire up the resistor and what value to use. Would it go between the - of the transistor and ENC +, or from - to ground, while - also goes to ENC +?

Chibs wrote: I'm afraid I don't fully understand how to wire up the resistor and what value to use. Would it go between the - of the transistor and ENC +, or from - to ground, while - also goes to ENC +?

There is a small diagram in the datasheet.