Using Input Transducer Characteristics to Design Voltage Dividers

The Role of Input Transducers in Voltage Dividers

Input transducers convert physical phenomena (such as temperature, light levels, or pressure) into electrical signals.
The two main types of input transducers are Active (self-generating) and Passive (depends on external power source).
Active input transducers produce their own electrical voltage or current, while passive transducers change their physical properties, such as resistance, in response to the physical phenomena.
These electrical signals can then be used in a voltage divider circuit to control the output voltage.
When selecting an input transducer for a voltage divider, it’s important to consider the transducer’s characteristic response to the physical phenomena it’s measuring.

The chosen input transducer’s characteristics should match the needs of the voltage divider circuit.
The resistance change of the input transducer in response to changes in the physical phenomena should be considered.
In designing a voltage divider, remember the output voltage is determined by the formula Vout = Vin * (R2 / (R1 + R2)), where R1 is the resistance of the fixed resistor and R2 is the resistance of the input transducer.
The output voltage of the voltage divider will therefore change based on the resistance changes of the input transducer, reacting to the physical changes it’s designed to measure.
Consider also the input transducer’s operational ranges (the minimum and maximum of the physical phenomena it can measure) and sensitivity (how fine or coarse the changes in resistance are in response to changes in the physical phenomena).
Adjust the values of R1 and Vin to achieve the desired output voltage range for the specific conditions that the transducer will be exposed to.

A real-world example is a voltage divider designed with an LDR (Light Dependent Resistor) to control lighting in response to changing daylight levels. The LDR’s resistance decreases as light levels increase.
If the goal is to turn on an LED when it gets dark, then the LDR should be R2 in the voltage divider. When it gets dark, the resistance of the LDR increases, increasing the Vout, which can then be used to power the LED.
Another example is a voltage divider with a thermistor used in a temperature control system. If the thermistor’s resistance decreases with increasing temperature, as an NTC thermistor would, it should be used as R2 in the voltage divider. As temperature increases, Vout will increase, which could drive a cooling fan.
Understanding the characteristics of the input transducer and how they change in response to the physical phenomena being measured is critical to designing effective analogue electronic control systems.