Why Is a Resistor Necessary?
Can we use a jumper wire connect to VCC or GND to setup the default state for button instead of using resistor? it will short the circuit
Current Consumption
To calculate the current when the button is pressed, we need to consider the current flowing through the resistor and the button in the circuit. When the button is pressed, the GPIO pin is directly connected to GND (in the pull-up configuration), bypassing the pull-up resistor. The current flow will be influenced by the resistor value and the voltage.
Circuit in Pull-up Configuration
- The button, when pressed, creates a direct path between the GPIO pin and GND.
- The pull-up resistor is in series with the GPIO pin and VCC.
- When the button is pressed, the GPIO pin is at GND, and the voltage across the pull-up resistor will be approximately 3.3V (VCC).
Formula to Calculate Current
Using Ohm’s Law:
$$I=VR$$
Where:
- I is the current through the resistor.
- V is the voltage across the resistor (3.3V in this case).
- R is the resistance of the pull-up resistor (approximately 45kΩ for the internal pull-up resistor of the ESP32).
Example Calculation
Let’s calculate the current assuming the ESP32’s internal pull-up resistor is 45kΩ.
$$𝐼=3.3𝑉/10,000Ω$$
$$𝐼≈0.0000733𝐴=73.3𝜇𝐴$$
Conclusion
When the button is pressed, the current flowing through the pull-up resistor is approximately 73.3 microamps. This is a very small amount of current, so the power waste is minimal.
use higher value resistor
Actually the pull-up resisor can be any values between 10k – 100k
why we cannot use higher value?
Effect of Using a Higher Resistor Value (100kΩ)
- Higher Resistance, Lower Current:
- A higher resistance (like 100kΩ) will result in a smaller current flowing through the pull-up or pull-down resistor when the button is not pressed. This reduces the power consumption, which can be beneficial in some low-power applications.
- Slower Response Time:
- The pull-up or pull-down resistor helps define the default state of the GPIO pin. With a higher resistance, the pin might take a bit longer to settle to the correct voltage level (especially when transitioning from high to low or vice versa), as the capacitor formed by the internal capacitance of the GPIO pin and the resistor will take longer to charge/discharge.
- The GPIO pin may not be as responsive to fast changes, which could be an issue in applications requiring fast, real-time responses.
- Susceptibility to Noise:
- A larger resistor (100kΩ) is more susceptible to electromagnetic interference (EMI) or noise, which can cause the GPIO pin to randomly float or pick up unwanted signals. A smaller resistor (like 10kΩ) provides a stronger connection to either GND or VCC, helping to prevent noise from affecting the signal.
- Internal Pull-up Resistor in ESP32:
- The ESP32’s internal pull-up and pull-down resistors are typically in the range of 40kΩ to 50kΩ, so using a 100kΩ external resistor would add a bit more resistance but still be within a tolerable range for most applications.
In Summary
- Can you use 100kΩ? Yes, you can, but it might lead to slower response times and increased susceptibility to noise.
- Should you use 100kΩ? For most general applications, 10kΩ is typically the preferred choice because it provides a good balance between current consumption, speed, and noise immunity.
If your application requires faster response times or is in a noisy environment, it’s generally better to stick with a 10kΩ resistor. However, if power consumption is more critical and response time isn’t an issue, a 100kΩ resistor can be used.
