UM1955 Datasheet, PDF (11/28 Pages) STMicroelectronics – Getting started with the multifunctional expansion board based on operational amplifiers for STM32 Nucleo

UM1955
5
Photodiode/UV sensor
Photodiode/UV sensor
This configuration can be used to monitor the ambient light and, for example, trigger an
action when a threshold level is reached.
5.1
Schematic diagram
Figure 6 depicts the circuit schematic of photodiode sensor configuration.
Figure 6. Photodiode configuration circuit schematic
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5.2
How to set up the expansion board
This configuration does not require any setup. Only the output voltage is reported. This
voltage is available on pin A4 of the Arduino UNO R3 connector and PC1 of the ST morpho
connectors (not mounted in the expansion board).
5.3
Measurement example
Here, three examples have been selected.
• Case 1: The board is placed inside a closed box. V_out = 33 mV (V_ol of the operational
amplifier which is saturating)
• Case 2: The board is in ambient light V_out = 420 mV
• Case 3: The sensor is below a light source V_out = 3.272 V (V_oh of the operational
amplifier which is saturating)
Depending on the needs of the application, it can be interesting to have current with better
sensitivity to darkness. In this case, it is recommended to increase the value of the R26
DocID028405 Rev 1
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