# Photoresistors sensitivity **URL:** \ **Category:** Sensors\ **Created:** [September 5, 2022, 12:38am UTC](https://forum.arduino.cc/t/photoresistors-sensitivity/1028704 "2022-09-05T00:38:59Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![antoniodelavega](https://avatars.discourse-cdn.com/v4/letter/a/8491ac/32.png) [@antoniodelavega](https://forum.arduino.cc/u/antoniodelavega)\ **Post date:** [September 5, 2022, 12:38am UTC](https://forum.arduino.cc/t/photoresistors-sensitivity/1028704/1 "2022-09-05T00:38:59Z")
Hello everyone! I'm working on solar tracker and now I'm testing the photoresistors. Here is the thing: I have two photoresistors (east and west). When these ones are not connected yet to 5V, I can measure an important resistance's change following the exposure to the light. BUT when I connect them and change the luminosity, I can notice the resistance's change is not as big as before, which make my photoresistors not really sensitive anymore (When I have a look on the serial monitor, I get max values like 8, 9 but no more, I guess I should get a value way higher between 0 and 1023 right?). I wanted to know if you guys already face this problem? Do you think my photoresistors are just counterfeits? Thank you for your help! PS: in the wiring diagram i also put north sensors but i don't use it in the code for now ```cpp void setup() { // Initialise la communication avec le PC Serial.begin(9600); } // Fonction loop(), appelée continuellement en boucle tant que la carte Arduino est alimentée void loop() { // Mesure la tension sur la broche A0 int valeur1 = analogRead(A0); valeur1 = analogRead(A0); int valeur2 = analogRead(A1); valeur2 = analogRead(A1); // Envoi la mesure au PC pour affichage et attends 250ms Serial.print("valeur1="); Serial.println(valeur1); delay(250); Serial.print("valeur2="); Serial.println(valeur2); } ``` ![photoresistor values](https://europe1.discourse-cdn.com/arduino/original/4X/2/c/9/2c93e8848dfecddd718affe4b4eb236349f2b8d8.png) ![Wiring diagram 1](https://europe1.discourse-cdn.com/arduino/original/4X/8/4/3/843e2bc5e8a3a539e35b3f69f9fa1e98c59a6d33.png) ![light test](https://europe1.discourse-cdn.com/arduino/original/4X/4/9/d/49d80bde346dc0a7e110a1489c617c165cb8355e.jpeg) ---
**Author:** ![ruilviana](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ruilviana/32/722429_2.png) [@ruilviana](https://forum.arduino.cc/u/ruilviana)\ **Post date:** [September 5, 2022, 12:49am UTC](https://forum.arduino.cc/t/photoresistors-sensitivity/1028704/2 "2022-09-05T00:49:53Z")
Hi, study the datasheet of your photoresitor. There you have the sensitivity/luminacia information. ---
**Author:** ![LarryD](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/larryd/32/215550_2.png) [@LarryD](https://forum.arduino.cc/u/LarryD)\ **Post date:** [September 5, 2022, 12:53am UTC](https://forum.arduino.cc/t/photoresistors-sensitivity/1028704/3 "2022-09-05T00:53:22Z")
Let’s assume the LDR has a dark resistance of 10k. You would start testing things with a series resistor (R2) of equal value (10k). ![image](https://europe1.discourse-cdn.com/arduino/original/4X/9/8/b/98b383b569963295aef26b9f78699f1e99792652.png) ---
**Author:** ![herbschwarz](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/herbschwarz/32/239314_2.png) [@herbschwarz](https://forum.arduino.cc/u/herbschwarz)\ **Post date:** [September 5, 2022, 1:07am UTC](https://forum.arduino.cc/t/photoresistors-sensitivity/1028704/4 "2022-09-05T01:07:21Z")
I do not see that the resistors are connected to ground. It seems they are 220 ohms and should be more like 10K for good readings. Also, the uppermost photoresistor is not connected to Vcc. ---
**Author:** ![johnwasser](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/johnwasser/32/214270_2.png) [@johnwasser](https://forum.arduino.cc/u/johnwasser)\ **Post date:** [September 5, 2022, 1:13am UTC](https://forum.arduino.cc/t/photoresistors-sensitivity/1028704/5 "2022-09-05T01:13:05Z")
> [@herbschwarz](#): > > I do not see that the resistors are connected to ground. Same here. The diagram shows the column NET TO the one connected to the resistor is connected to Ground. The resistor and the wire to Ground should be connected to the same column of five holes. ---
**Author:** ![antoniodelavega](https://avatars.discourse-cdn.com/v4/letter/a/8491ac/32.png) [@antoniodelavega](https://forum.arduino.cc/u/antoniodelavega)\ **Post date:** [September 5, 2022, 4:28am UTC](https://forum.arduino.cc/t/photoresistors-sensitivity/1028704/6 "2022-09-05T04:28:26Z")
Thanks for your first answers. Actually I used Fritzing for the wiring diagram and for some reasons they don't have 10 kOhms in their library (that's why i put 220 Ohms in the diagram) but I do confirm I use 10 kOhms in my electrical wiring. I changed the wiring as you said (see the joined diagram) but still I only have max 8 or 9 (I noticed the voltage is around 5.06V at the terminals of the LDR - normal light - maybe this out of the range 0 - 5 V is the cause of that?) Regards ![Wiring diagram 2](https://europe1.discourse-cdn.com/arduino/original/4X/3/6/9/369d9309c2c7220fb9a80b246a9c0b31fc4ee586.png) ![Wiring diagram picture](https://europe1.discourse-cdn.com/arduino/original/4X/d/d/b/ddb182990010fd11027dd8a3e0eb7491b9b8cf26.jpeg) ---
**Author:** ![antoniodelavega](https://avatars.discourse-cdn.com/v4/letter/a/8491ac/32.png) [@antoniodelavega](https://forum.arduino.cc/u/antoniodelavega)\ **Post date:** [September 5, 2022, 9:36am UTC](https://forum.arduino.cc/t/photoresistors-sensitivity/1028704/7 "2022-09-05T09:36:53Z")
Hey, I come back to you guys! Turned out my wiring diagram was ok. I just decided to disconnect my arduino board from the arduino motor shield (you know when all pins are connected, doing a stack with motorshield upwards and arduino board down) and connect only the pins necessary (direction, brake, power, ground and 5V). Now I get normal values between 0 and 1023, making the LDR more sensitive! Anyway, Thank you for your help ! ---
**Author:** ![PaulRB](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/paulrb/32/216330_2.png) [@PaulRB](https://forum.arduino.cc/u/PaulRB)\ **Post date:** [September 5, 2022, 9:46am UTC](https://forum.arduino.cc/t/photoresistors-sensitivity/1028704/8 "2022-09-05T09:46:41Z")
> [@antoniodelavega](#): > > I used Fritzing for the wiring diagram and for some reasons they don't have 10 kOhms in their library It's a generic resistor symbol, not a 220R-only resistor symbol. The default is 220R but you can set it to any value you want. ---
**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\ **Post date:** [March 4, 2023, 9:47am UTC](https://forum.arduino.cc/t/photoresistors-sensitivity/1028704/9 "2023-03-04T09:47:24Z")
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