THERMOMETER
Home > Group Projects > Thermometer Project
UPDATED:.21:27 21 October 2014

INTRODUCTION:

An accurate thermometer with 12 LEDs ranging from 8C to 30C

There are 12 LEDs on the display representing 2 degree Celsius steps. If 2 LEDs are on, then the temperature reading is in between the two. This circuit uses a micro-controller with a program running inside. It runs from 2 AA batteries which should last many weeks.

This circuit can be applied to a range of themes to create a variety of projects.

This project is available in our shop now!.


CIRCUIT DESCRIPTION
The circuit is based around a PIC micro-controller that has a program running.

The temperature sensor is a thermistor (TS1) which is connected into a potential divider by R7. The output voltage from the potential divider is sampled by the ADC (Analogue to Digital Converter) inside the PIC and is given a value from 0-255 which is proportional to the voltage.

The sampled value is turned into the final LED output with a little maths and displayed on one of 12 3mm LEDs. These are calibrated in 2 degree Celcius steps.

Circuit Diagram

The PCB is in the shape of a traditional thermometer due to the line of 12 LEDs and overall measures 4.05" x 1.1" (103mm x 28mm)

The PCB has markings on showing the temperature each LED represents in Celsius and Fahrenheit.

CONSTRUCTION

The LEDs can be soldered directly to the PCB and use the scale on the PCB as part of the finished product.

Alternatively, a spacer can be used to set all the LEDs at the same height. This can be piece of 1.5mm thick material such as HIPS or acrylic cut to a height of 7mm.

The holes 3mm in diameter and spaced 6mm apart from center to center.
An outline template of the PCB is available below - Resources
These models were made from acrylic which has a good finish, comes in a range of colours and can be shaped with a strip heater. A laser cutter enables complex shapes to be cut and accurate drilling for the holes for the LEDs.

With the LEDs extended, they should protrude through a panel of 2-3mm with room for the rest of the components to sit behind it.

A stand cut and shaped can be used to hold the battery and the PCB into place since fixing to acrylic is not as easy as wood.

Using wood is an easier process where the shapes that piece together can be cut by hand or by using a powered fret saw

The eagle is designed to be wall hung and has a wire connected to each wing to suspend it from.


POWER SUPPLY RESOURCES
The power supply is from 2 AA batteries. The current consumption of the circuit is about 2.4mA with one LED and 5.1mA with two. Overall it averages to about 3.7mA which means 2 AA batteries should last many weeks.

Step-by-step PCB Assembly Guide - PPT

Templates for PCB - WORD

PCB Template Image - JPG

PCB Template 2D - DTD

There are kits available from our shop pages in packs of 1x, 10x and 50x offering bulk discount.
There is also just the IC available in packs of 10.

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