# Enhancing Meteor Observations with Photodiode Detectors
## 3 Concept  
In this chapter, we will present the general concept of the sensor used for meteor observation. The presented device is designed to complement existing CCD/CMOS meteor observation systems by functioning as an all-sky, high-speed photometer. The one-dimensional brightness data it produces require significantly less storage compared to standard CCD/CMOS imagery, enabling simultaneous data acquisition alongside camera recordings. Furthermore, its relatively low cost makes it an attractive option for straightforward integration into already operational meteor CCD/CMOS-based stations. Rather than replacing traditional imaging approaches, the device supplements them by providing continuous photometric data that can aid in event classification and enhance the overall accuracy of meteor observations. The key sensing element is the PS100-6b photodiode (TE Connectivity [[https://eu.mouser.com/datasheet/2/418/9/PS100_6_THD_3001054-3304769.pdf](https://eu.mouser.com/datasheet/2/418/9/PS100_6_THD_3001054-3304769.pdf)]([https://eu.mouser.com/datasheet/2/418/9/PS100_6_THD_3001054-3304769.pdf](https://eu.mouser.com/datasheet/2/418/9/PS100_6_THD_3001054-3304769.pdf)), accessed date: 2 March 2025). It features a 10 mm \(\times\) 10 mm light-collecting area and, according to the manufacturer's specifications, achieves up to 90% quantum efficiency with a low dark current. Table 1 presents the main device parameters taken directly from the datasheet, while Figure 1 shows the typical spectral sensitivity as provided by the manufacturer. The meteor detection system we designed utilizes photodiodes facing the zenith to allow light to fall directly upon them without the use of additional lenses. This approach is both judicious and advantageous for several reasons. Firstly, the primary objective of our sensors is not to create images but to record fluctuations in light intensity from the night sky. In this context, the collecting area of the sensor is crucial, determining its capability to detect faint light sources. Using short focal-length lenses (e.g., 2-3 mm) would significantly reduce the photodiode's effective collecting area. Even for lenses with a high brightness (e.g., F# = 1), the lens's collecting area would be incomparably smaller than that of a 10 mm \(\times\) 10 mm in our photodiodes. Secondly, wide-angle lenses with very short focal lengths and large collecting areas tend to be costly. Our aim is to increase the number of detectors while maintaining the affordability of each module, making cost-effectiveness a priority. Each photodiode is connected to an operational amplifier, which converts the small currents (pico amperes) generated by the diode into voltages. Each module, consisting of a diode and two operational amplifiers, was placed on an independent PCB. The design of these boards was intended to minimize any kind of noise given the extremely small currents generated by the diode when recording the night sky. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter Name** & **Symbol** & **Value** & **Unit** & **Test Condition** \\ \hline Active area & \(A_{a}\) & 10 \(\times\) 10 & mm & - \\  & & 100 & mm\({}^{2}\) & \\ Dark current & \(I_{D}\) & 1 & nA & \(V_{R}\) = 5V \\ Capacitance & C & 720 & pF & \(V_{R}\) = 0 V \\  & & 275 & pF & \(V_{R}\) = 5 V \\ Responsivity & & 0.22 & A/W & \(\lambda\) = 410 nm \\  & & 0.37 & A/W & \(\lambda\) = 550 nm \\ Rise time & \(t_{R}\) & 200 & ns & \(V_{R}\) = 5 V; \(\lambda\) = 410 nm; \(R_{L}\) = 50 \(\Omega\) \\ Noise Equivalent Power & NEP & 5.8 \(\times\) 10\({}^{-14}\) & W/\(\sqrt{\rm Hz}\) & - \\ \hline \hline \end{tabular}
\end{table} 
Table 1: PS100-6b photodiode parameters (\(V_{R}\) is the reverse voltage applied to a diode, \(R_{L}\) is the load resistance connected to a diode when measuring the rise time). Figure 1: Quantum efficiency of the used PS100-6B-CER photodiode. Four independent photodiode-amplifier modules are connected to a single ADuC7020 microcontroller (Analog Devices, Norwood, MA, USA).