Summary of Digital thermometer with PIC16F84 circuit
This project describes a simple digital thermometer using the PIC16F84A microcontroller. It leverages the watchdog timer (WDT) time-out period variations, influenced by temperature, to measure temperature without a separate sensor. The system operates primarily in low-power sleep mode and wakes up upon a key press to display or calibrate temperature readings. It offers three modes: Sleep, Display, and Calibration, enabling precise temperature measurement with minimal external components and low cost.
Parts used in the Digital Thermometer with PIC16F84A:
- PIC16F84A microcontroller
- LEDs (for temperature display)
- Push-buttons (for TEMP and calibration keys)
- Power supply (battery or regulated source)
- Supporting passive components (resistors, capacitors)
This electronic project is a very simple thermometer that is based on the PIC16F84A microcontroller, designed by Microchip.
Why to use a thermometer that is designed using a microcontroller and not a classic analog thermometer? Because you can design a complex solution using few external components, resulting an low cost application that provide a high precision measurement .
This Digital thermometer microcontroller project use watchdog timer function to measure temperature. The WDT on all PIC-micro microcontrollers has a nominal time-out period of 18 ms. The WDT time-out period varies with temperature, VDD and part-to-part process variations.Without using a separate temperature sensor, it is possible to calculate the temperature with reasonable accuracy using the WDT time-out period.
To translate the environment temperature into an actual reading, the system must be able to do the following:
• Provide a method for establishing time-out to temperature calibration
• Count the number of WDT time-outs for a given period of time
• Equate the number of time-outs to a temperature
The PIC16F84A microcontroller is normally in SLEEP mode, consuming
very little operating current but if any key is pressed, it ‘wakes up’ from SLEEP and updates the WDT count, and checks for additional key presses. If there are none, it returns to SLEEP mode.
The WDT Thermometer has three distinct operating modes:
SLEEP Mode: This is the default mode the system starts in when power is applied .Display Mode: When the TEMP key is pressed, the system wakes up and the LEDs show the temperature
in degrees Centigrade.
Calibration Mode: This mode creates a set of new calibration values, in addition to those present in the firmware.
For more detail: Digital thermometer with PIC16F84 circuit
