photons and electrons in the same place

Optoelectronics is dedicated to studying and designing systems that have interaction with photons and electrons, simply any object or thing related to light and electronics, such as mobile phones, electronic devices, etc.

Optical sensors

The main optical sensors are photoresistors, LDR (Figure 1). Remember that these were resistors whose value decreased with light, so when they receive a beam of light they allow the passage of electrical current through the control circuit. In this way we can feel the light emissions produced by a source that is in the operating range of our photoresistor.

Figure 1. Photoresist sensors.

Measure sars-cov-2 with a photoresist

For this project, it is considered to measure the light produced by a fluorescent reaction that is proportional to the amount of virus in a sample. The emission ranges from 500 to 580 nanometers (nm) which is still in the visible spectrum (see figure 2). So it can be detected with high precision with a simple light-dependent resistor (LDR) and the following circuit is considered feasible to condition the signal we want and determine, by means of a calibration curve, the voltage corresponding to the quantity virus in the sample.

Figure 2. Visible light spectrum

The idea is to generate these function jumps or to generate signal conversions to be able to easily quantify with an electronic device and tell us if a sample is infected by SARS-CoV-2. Below is a simulation of how the data acquisition of our system would ideally be, as well as the output in an electrical signal that we can quantify.


Figure 3. Graph of fluorescent emission versus electrical resistance of photoresistor

Figure 4. Graph of the electrical resistance of the photoresist against the voltage at the output of the circuit

Electronic data acquisition

Below is a possible circuit to process the fluorescent light emission signal and determine whether a test is positive or negative. This system lights a green LED if the test does not have sufficient presence of the SARS-CoV-2 virus, while it lights a red LED if the detected sample is outside the established limits.


[1] N. Nise, Control systems engineering, 6th ed. Norman Nise, 2006.
[2] Linear ICs and Operational Amplifiers Robert F. Coughlin and Frederick F. Driscoll Prentice Hall Fifth Edition 1998