As an amateur to breadboarding I'd been learning about transimpedance amps and photodiodes earlier this year for a project. Eventually I picked up a phototransistor (3DU5C) at a hobby shop, mistaking for a PD, so I learned a bit about them and found this circuit on physics portal after failing to get any readable voltage from a common-collector circuit:
The first time I tried the circuit using Arduino as a voltmeter I'd forgotten to hook up the Vcc- pin on the op-amp to GND, but the transistor responded to light (4.18V at ambient light and ~4.75V with a phone flashlight. When I noticed it, I completed the power supply to the OA and it started reading 5.00V consistently. Hooking up one power pin to different ports produced other various ranges, the highest being the Vcc port to GND (1.35-4.07). The transistor also seems to work with no power supply to the OA at all. Additionally, all cases seem to be switch mode. Any idea why this is, and how could I change this circuit to active mode?