Digital Vernier Caliper for Length Measurement Using LVDT and Arduino Uno.

In this Instructable I'm going to discuss how to make a digital Vernier caliper using LVDT. As we know transformer is a linear device, we are going to use LVDT i.e. linear variable differential transformer. We are going to use an oscillator circuit for excitation of the transformer primary. The frequency of this oscillator is 55 Khz. At the secondary of this oscillator we shall use a rectification circuit and feed the DC voltage to Arduino Uno.

Bill of materials

1. Ferrite rod as per availability (I used 20cm long rod)
2. Paper bobbin (Make suitable paper bobbin as per the rod dimensions)
3. Copper wire. (Refer video for turns)
4. IC555
5. 1K resistor X 2
6. 0.01uF capacitor X 2
7. Bread board
8. Arduino Uno
9. Schottky diode.
10. Filter capacitor 10uF/63V

Refer attached circuit.

The application consists of three parts :

1. LVDT: Linear variable differential transformer i.e. the LVDT is used to detect the change in position (mm). The LVDT uses a linear ferrite rod as the core. The rod moves up and down linearly inside a paper bobbin. The bobbin is wounded with several turns of insulated copper wire. The LVDT is a transformer basically and it is excited with a high frequency source. Here IC 555 works as the excitor.
2. Excitation circuit: This circuit is based on IC555. This excitor generates a frequency of 45KHZ and excites the primary of the LVDT. There is a voltage developed at the LVDT secondary due to this excitation. As we move the core, this secondary voltage changes.
3. Detector circuitry: The detector circuit consists of a rectifier filter network and fed to Arduino Uno. Arduino Uno receives this detector output at Analog channel 0. The data is processed and displayed on LCD display.