Explaination of resistor used in 1st project of iot

please explain the use of resistor in light sensor project?
I am not able to understand why is voltage divided among the arm of resistor.

@modiharshit01 we use resistor in light sensor project in order to maintain the safety of LDR. If by any chance due to some fluctuations in voltage may affect the LDR working or even damages it completely, so to avoid it we use resistor as safety device as it maintain the voltage flow and the principle behind voltage dividing among the arm of resistor is based on ohms law(V=IR). According to it voltage is directly proportional to resistance, based on it LDR value will impact the voltage. Hope i had given a useful answer to your issue.

Why did we use 10k ohm resistor?

LDR is a device whose resistance changes on the amount of light that is received by it. Usually it has a very high resistance. If it is dark, the resistance will be more and if it is more bright then the resistance will be less. According to Ohm’s law, V=IR i.e. Voltage = product of Current(I) and Resistance®. So as the resistance increases, the voltage will increase and if resistance is less, voltage will be low. The arm with more resistance will have more voltage across it and vice-versa. The resistor plays an important role for safety. Plus it may act as a reference point as we know the value of it’s resistance(10k).

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but what about the equations needed in the product. In the video A0 is used directly

Could you elaborate on your question?

Hi @devananthvijayan,
The first project does not use any other equations directly. The concept referred to in the video is also only Ohm’s Law, which is given in the video and has been explained previously in this thread. The A0 that you mentioned is the pin that takes the analog input for an ADC (analog to digital converter) which uses a couple of other steps like sampling (we are taking a new value every 5min, thus 1/(5*60) will be the sampling rate in Hertz) and quantization. In short, there is more of an algorithm/process involved as compared to named mathematical equations, the implementation of which is already done through hardware within the Bolt chip. That is why we only connect to the A0 pin, which only helps facilitate the IoT aspect of the device, and does not add to the main function of the circuit, which is to record the intensity of the light source.

the quantity to be measured is light intensity but what we find is voltage across the resistor right? I wanted to know how that works in solving the problem.

So V=IR, right? We know the total voltage supplied, which is standard across the country (220V), and depending upon how much current the resistor can handle, we also fix resistance (10k Ohm). The remaining resistance supplied to the circuit varies depending upon the light intensity and is again used in the same equation. We then use the relation between intensity and resistance, since we now know the values of all involved quantities (current, voltage and resistance). Hope this clarifies.

@modiharshit01 Ohm’s law states that the voltage or potential difference between two points is directly proportional to the current or electricity passing through the resistance, and directly proportional to the resistance of the circuit. The formula for Ohm’s law is V=IR. When the light is absorbed by the material then the conductivity of the material enhances. When the light falls on the LDR, then the electrons in the valence band of the material are eager to the conduction band . But, the photons in the incident light must have energy superior to the bandgap of the material to make the electrons jump from one band to another band (valance to conduction).Hope you understand the concept.

These resistors are frequently used as light sensors. These resistors are mainly used when there is a need to sense the absence and presence of the light such as burglar alarm circuits, alarm clock, light intensity meters, etc . LDR resistors mainly involves in various electrical and electronic projects.thats why we use resistors in ligh sensor project

@devananthvijayan what kind of project are you trying to make and what kind of equations are you looking for?

Mostly you’ll use

V=IR(Ohm's Law)
V=Potential Difference/Voltage
I=Current(in amperes)

Check out this playlist to learn more.

ok, thanks for helping

Hello , I am Sanjeevni. The answer to your question is:-
Ans.In light sensor project , resistor is used to measure the light intensity. To know how bright the light is ? Resistors are used to indicate the presence or absence of light.

Voltage is divided among the arm of resistors to reduce the magnitude of voltage or to create a reference voltage and also used at low frequencies as a signal attenuator.
We use LDR in one of the arms of Voltage divider circuit. It pulls a voltage across it which is proportional to its resistance. By Ohm’s Law, V=IR.
When resistance of LDR increases so the voltage is pulled by it.

Suppose you don’t connect the resistance in series with the LDR, the supply voltage to the bolt device will appear across the LDR irrespective of light intensity falling onto it. As a result, we can’t measure the varying light intensity. So, we create a voltage divider circuit by connecting LDR and the resistance of desired and chosen value(a voltage divider circuit is simply a series connection of resistors connected to a voltage source), so that the total voltage drop across the combination of LDR and external resistance is fixed, but depending upon light intensity voltage across LDR varies and the rest voltage appears across the external resistance and we get our desired data points.

Hello , I am Sanjeevni.
The answer to your question is:-

Ans. With increasing light intensity , the resistance of a LDR decreases . Strong light - LDR resistance decreases to 0 ohms . So 10k ohm resistor sees closer to 5V.

The key point of Bolt IoT also has Vcc (5V) and ground. As for the given voltage Vcc (5V) in Bolt IoT resistor mainly use 10k ohm resistor and we can use other resistor which should be in minimum range 800 ohm - maximum range 1.2k ohm . Otherwise if we will go above of this resistor this might give false result in output.

Resistor also vary in which LDR we are implemented on it.

We use 10k ohm resistors because 10k ohm resistors make excellent pull -ups , pull downs, and current limiters.