“The project presented here is a photodiode amplifier for visible light. The output voltage of the circuit increases linearly with light intensity. Low-cost BPW34 photodiode is used as a light sensor and OPA381 op-amp as an amplifier. OPA381 is a transimpedance amplifier that converts photodiode current flow into voltage. The operating voltage of this circuit is 5V DC, and output ranges to almost 0V to 4.5V DC. The project can be used to make a LUX meter and other photo lab equipment. The analog output of the project is within the range of microcontroller’s ADC for easy interface with micro-controllers. By combining this project with Arduino and LCD, you can create a light meter for photography. It is advisable to use filters in front of the sensor to stop infra-red noise as the sensitivity of BPW34 is near to infrared. Half-cut table tennis ball will help as a filter.
OPA381 Precision, Low Power, 18MHz Transimpedance Amplifier: The OPA381 family of transimpedance amplifiers provides 18MHz of Gain Bandwidth (GBW), with extremely high precision, excellent long-term stability, and very low 1/f noise. The OPA381 features an offset voltage of 25μV (max), offset drift of 0.1μV/°C (max), and bias current of 3pA. The OPA381 far exceeds the offset, drift, and noise performance that conventional JFET op amps provide. The signal bandwidth of a transimpedance amplifier depends largely on the GBW of the amplifier and the parasitic capacitance of the photodiode, as well as the feedback resistor. The 18MHz GBW of the OPA381 enables a transimpedance bandwidth of > 250kHz in most configurations. The OPA381 is ideally suited for fast control loops for power level measurement on an optical fibber. As a result of the high precision and low-noise characteristics of the OPA381, a dynamic range of 5 decades can be achieved. This capability allows the measurement of signal currents on the order of 10nA, and up to 1mA in a single I/V conversion stage. In contrast to logarithmic amplifiers, the OPA381 provides very wide bandwidth throughout the full dynamic range.”