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--- eeng:topics:photocells:start [2022/10/17 11:34] – rolf
+++ eeng:topics:photocells:start [2023/11/22 01:07] (current) – [About LDR] rolf
@@ Line 1: / Line 1: @@
 ====== Photocells / Light Dependent Resistors (LDR) ======
+===== Lecture Slides =====
-| {{https://cdn.sparkfun.com//assets/parts/2/4/6/2/09088-02-L.jpg?200&direct}} |
+  * {{ :eeng:topics:photocells:ldr_2022-09-22_v001_rb.pdf |}}
+===== About LDR =====
+| {{https://cdn.sparkfun.com//assets/parts/2/4/6/2/09088-02-L.jpg?200}} |
 | Fig.: A cadmium sulfide (CdS) photocell. \\ (Source: [[https://www.sparkfun.com/products/9088|SparkFun]]) |
@@ Line 13: / Line 18: @@
   - {{https://resources.perkinelmer.com/corporate/cmsresources/images/dts_photocellsa9050.pdf|Photocells A 9050, A 9060}}.
-=== High Variability ===
+==== Large Variance among specimen of the same product series ====
+The GL5528 datasheet from Sparkfun illustrates the broad performance variety between LDR of the same type:
+  * :!: https://cdn.sparkfun.com/datasheets/Sensors/LightImaging/SEN-09088.pdf
+==== LUX ====
+The light "intensity" illuminating the photocell is measured in **Lux**. This unit takes not just the physical light quantity but also the sensitivity of the human eye into account. It combines physics with physiology.
+"The lux (symbol: lx) is the **unit of illuminance, or luminous flux per unit area,** in the International System of Units (SI). It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. It is analogous to the radiometric unit watt per square metre, but with the power at each wavelength weighted according to the luminosity function, a standardized model of human visual brightness perception. In English, "lux" is used as both the singular and plural form." (from [[https://en.wikipedia.org/wiki/Lux|Wikipedia]])
+==== High Performance Variability ====
 Do not trust the resistance-vs-lux curves too much. Adafruit states on its tutorial on Photocells for Arduino:
@@ Line 20: / Line 42: @@
 | {{https://cdn.sparkfun.com/assets/learn_tutorials/5/1/2/illuminance-vs-resistance.png?400&direct}} |
-| Fig.: Typical performance variation of a photocells (log-log-plot). \\ (Source: [[http://cdn.sparkfun.com/datasheets/Sensors/LightImaging/SEN-09088.pdf|GL 5528 Photodetector by SparkFun)]] |
+| Fig.: Typical performance variation of photocells of the same type (log-log-plot). \\ (Source: [[http://cdn.sparkfun.com/datasheets/Sensors/LightImaging/SEN-09088.pdf|GL 5528 Photodetector by SparkFun)]] |
 The [[http://cdn.sparkfun.com/datasheets/Sensors/LightImaging/SEN-09088.pdf|datasheet]] on GL5528 Photocell by **SparkFun** reflects these uncertainties.
-=== LUX ===
-The light "intensity" illuminating the photocell is measured in **Lux**. This unit takes not just the physical light quantity but also the sensitivity of the human eye into account. It combines physics with physiology.
+===== LDR Voltage Divider Experiment with Arduino =====
+| {{ :eeng:topics:photocells:ldr_arduino_schematic_v001.png?direct&400 |}} |
+| Fig.: Schematic. |
+| {{ :eeng:topics:photocells:ldr_arduino_breadboard_v001.png?direct&400 |}} |
+| Fig.: Breadboard view. |
+===== Arduino Code: ADC to Serial =====
+<code c++ LDR_V001.ino>
+/*
+ * Voltage divider with LDR
+ *
+ * Circuit:
+ * 5V (Vcc) - LDR - R1 - GND
+ * The node between LDR and R1 (V1, voltage drop across R1) is connected to analog input A0
+ * R1 arbitrary, e.g. 10kOhms
+ *
+ * The voltage V1 is converted to a digital number (dn) by means of an analog-to-digital converter (ADC).
+ * The range of dn: 0 <= dn <= 1023 (10 bit resolution)
+ *
+ * Conversion:
+ * V1 = 0V -> dn = 0
+ * V1 = 5V -> dn = 1023
+ *
+ * Reconstruction of voltage from digital number:
+ * V = dn / 1023 * 5V
+ *
+ */
-"The lux (symbol: lx) is the unit of illuminance, or luminous flux per unit area, in the International System of Units (SI).[1][2] It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. It is analogous to the radiometric unit watt per square metre, but with the power at each wavelength weighted according to the luminosity function, a standardized model of human visual brightness perception. In English, "lux" is used as both the singular and plural form." (from [[https://en.wikipedia.org/wiki/Lux|Wikipedia]])
+int AIN = A0; // Analog input pin number
+void setup() {
+  // put your setup code here, to run once:
+  Serial.begin(115200);
+  Serial.println("dn  V  mV");
+}
+void loop() {
+  // put your main code here, to run repeatedly:
+  int  dn = analogRead(AIN); // digital integer number between 0 and 1023 (10 bits, 2^10 different values)
+  float V = (float)dn / 1024 * 5.0; // convert dn to float first, then divide by 1024
+  int  mV = V*1000; // millivolts, converted from float
+  Serial.print(dn);    // print to serial without a newline at the end, i.e. the next print is in the same line
+  Serial.print("  ");  // spaces
+  Serial.print(V);
+  Serial.print("  ");
+  Serial.println(mV);  // last print with newline, i.e. the next print will be in the next line.
+  delay(100); // pause in ms, 100 ms means 10 meas / sec.
+}
+</code>