Questions on LDR Circuit in the Training Module

I had the following two questions…

  1. What is the circuit diagram of the LDR project in the training?
  2. Why do we connect the resistor to the GND pin and A0 along with the LDR?

@lankabhedi here are the answers:

  • Step 1: Insert one lead of the LDR into the Bolt Module’s 3v3 Pin.
  • Step 2: Insert other lead of the LDR into the A0 pin
  • Step 3: Insert one leg of the 10k Ohm resistor into the GND pin
  • Step 4: Insert the other leg of the resistor also into the A0 pin

Note: Make sure that at no point do the 3.3V (or even 5V) and GND pins or wires coming out of them touch each other. If you short power to Ground without a resistor even accidentally, the current drawn might be high enough to destroy the Bolt module.

You can visit the Project 1 section to confirm the hardware connections.

Hardware Connections are as follows:

  1. We connect the resistor to the GND pin and A0 to the LDR as to implement the concept of VOLTAGE DIVIDER CIRCUIT.

As Light Dependent Resistor (LDR) changes its internal resistance depending on the light conditions.
More the light = Less the resistance
Less the light = More the resistance

So, in order to make the LDR sense the light intensity we have to transform the change in the resistance to change in voltage. So this will be achieved by the Voltage Divider Circuit

(The circuit breaks down the voltage into smaller voltages at each arm of the circuit. As ‘V’ voltage is coming to the Resistor R1, so there will be drop of V1 voltage and LDR will get a voltage of (V - V1) voltage and there will be a drop of V2 voltage)

The hardware connection for the actual project is different, we place the LDR in the first place and then a resistor of 10k ohm (Black, Brown, Orange) is placed as the second arm.

Resistor of 10k ohm is required because of the fact that the Analog 0 (A0) pin of bolt module operates for a voltage level of 0 - 1 V and we provide a 3V voltage to LDR. Due to the internal resistance of the LDR, the voltage level drops to a certain level but still that level is not within the 0-1V range in which the A0 pin capture the readings correctly.

Therefore, we have to use a resistor (which offers a resistance of 10k ohm) in order to make the voltage, going into the A0 pin, in the range of 0 - 1 V.
Note: We have to specifically use resistor of 10k ohm because 03 V voltage from the Bolt module can be converted in the 0 -1 V range only by the internal resistance of the LDR and an external resistance of 10k ohm.

I hop I have answered your query. So do mark the solution


Thank you so much @harshika1406.vats! :blush: