Arsenic Prototype 5.0
This device builds on prototype 4.0 hardware but introduces a major change in the detection part. Namely, we replace the digital light sensor TSL235R by a low noise photodiode together with a low-noise amplifier OPA333. The measurement using a continuous light source is also replaced by modulated light together with a digital lock-in amplifier. The modulated light with lock-in amplifier allows to operate in the low-noise regime of the op-amp and also reject ambient noise leading to a design less sensitive to poor light insulation of the detector.
The amplifier circuit is a single-sided supply based on a T-network as pictured.