Tuesday, January 24, 2012

High resolution digital capacitance meter

This digital cap. meter from RomanBlack provides capacitance measurements ranging from 0 pF to 50 uF with a resolution of 0.01 pF. It uses the on-chip analog comparator of PIC16F628 microcontroller as an oscillator whose frequency is controlled by an external resistor and a capacitor (to be measured). Since the resistor is fixed, the capacitance value can be determined by measuring the frequency of oscillation.

Friday, January 20, 2012

Reading multiple switches from one I/O pin

Normally one input switch requires one digital input pin of a microcontroller. Use of keypad style multiplexing saves some input pins while interfacing an array of switches. There exist another technique based on ADC channel that allows to connect multiple switches on a single input pin of a microcontroller. This tutorial from Embedded Lab demonstrates this as applied to PIC12F683 microcontroller.

DHT11 sensor protocol and its interface with PIC microcontroller

DHT11 is the most inexpensive calibrated digital sensor currently available in the market for measuring relative humidity and temperature together. However, it has got its own proprietary 1-wire protocol which makes it little challenging to interface with microcontrollers. Raj from Embedded Lab shows how to implement this protocol in the firmware of PIC microcontroller so that the temperature and relative humidity information can be retrieved from the sensor.