Are you an electronic hobbyist? Then an adjustable power supply is a must for your various needs. This project explains how to make a LM317 based adjustable power supply unit with a digital display.
1. LM317 IC
2. Resistor – 240 Ohms
3. Capacitors – 0.1uF, 10uF
4. Potentiometer – 5k
5. 30V/1A Adapter (or a transformer + Bridge wave rectifier IC)
6. ATMega16 Developments Board
7. 16 x 2 LCD Board
Well the power supply circuit is very simple and can be found in the datasheet of LM317 itself.
What we need to design is the additional voltmeter kind of arrangements using a microcontroller in order to display the output voltage value accurately. For this, we use the ADC feature of the microcontroller.
But the problem is that ATmega16 can only take up to 5V. Input voltage more than that can fry up the controller.
Solution: A Voltage divider circuit!
Here R1 and R2 are the resistors and Vin is the input voltage. The output voltage Vout is given as:
Vout = Vin X R2/(R1 + R2) . . . . . . . . . . . . . . . (1)
We choose the resistor values based on our requirements. Like say now our maximum voltage to be measured is 30V but we can only give up to 5V to our controller.
For more detail: Variable Power Supply with LCD