Introduction

The aim of this project was to produce a stand-alone module which displays the current time, date and temperature. A Programmable Interface Controller (PIC), which is a single-board computer, is used to continually update the Liquid Crystal Display (LCD) with the time and date obtained by radio from the National Physical Laboratory in Rugby, and the temperature obtained from a digital thermometer chip. The completed module that we made is able to synchronise itself with the radio signal at power-on and maintain the display.

Hardware Description

The equipment used in our project is the following :

16C84 Programmable Interface Controller (PIC), by Microchip

The Programmable interface controller is an integrated circuit which can be programmed to execute instructions. The PIC was programmed in assemply language.

It operates at a speed of 4MHz clock input. The PIC has 13 I/O ports which are used in the following way :

• 7 for communicating with the LCD.
• 3 for the thermometer.
• 1 for receiving the output from the Receiver Module.
• 2 for the Control Panel.

The TLCM2040 Liquid Crystal Display (LCD) Module.

This has four lines of 20 characters. It includes a build in HD44780 controller. This controller has its own instruction set and provides the LCD with a range of features. These features are :

• The use of 160 predefined 5x7 dot characters
• 8 user defined characters
• A number of instruction functions, such as swithcing the cursor on and off in the display, or making the characters appear in the display from right to left and vice-versa.

The module can be interfaced to either 4-bit or 8-bit MPU. In our case due to the small number of I/O ports for communication with the PIC the 4-bit interfacing mode had to be used.

Antenna & EM2 Receiver Module, by Galeon Systems Ltd.

The Antenna together with the Receiver Module provide us with a digital output corresponding to the transmitted time and date information. The receiver is operating at a fixed frequency of 60KHz which is the required frequency for reception of the MSF time service transmitted from Rugby. The signal received is converted to a digital output by the receiver module. and the appropriate software is required to decode this output.

The signal sent by National Physical Laboratory is converted to a digital output by the receiver module. The signal contains information about the current date and time. This information is converted to a binary digital output by the receiver module. The digital output we get is a pattern of bits updated every minute. In this pattern each element of the current date and time is coded in a specific way.

The first 8 bits of the pattern represent the year, the next 5 represent the month. The next 6 bits represent the date of the month and the next 3 the day of the week. After that we get the time in a similar way. The following 6 bits represent the hour of time and the next 7 bits represent the hour.

After that a unique pattern of 8 bits appears in the signal which remains the same every time the signal is updated. This is to let us know when the translation of the signal should begin. After having received this unique pattern we start receiving the information to be displayed on our clock.

Every second one bit is transmitted and the signal is updated every minute. 59 seconds of the minute contain all this information in one bit per second. The 60th second all the information is transmitted again compressed in just one second. The 59 seconds are called the slow code and the compressed informartion in just one second is the fast code.

DS1620 Digital Thermometer, by Dallas Semiconductor.

The thermometer chip provides 9-bit temperature readings which indicate the temperature of the device, in two's complement format. Temperature readings and settings, ie. the communication to and from the thermometer is all done over a simple 3-wire serial interface.

The features of the thermometer are :

• It requires no external components for its operation.
• It measures temperatures from -55 to 125 degrees Celcius in 0.5 degree increments. The Fahrenheit equivalent is -67 to 257 degrees in 0.9 degrees increments.
• The temperature is read as a 9-bit value.
• It converts temperature to a digital word in 200ms.

The Control Panel.

This is the main part from which the user communicates with the clock. It is composed by switches that provide the clock with a number of features. The operations of the switches are :

• On/Off switch used for turning the clock on and off.
• Reset Switch used for resetting the PIC.
• C/F degrees used for temperature conversion between degrees Celcius and Fahrenheit.
• 12/24 hours switch used for displaying the time in 12 or 24 hour mode.
• Signal Reception switch. This is for choosing whether the signal we receive is coming from the inbuilt antenna of the clock or from an external antenna that can be connected through a specially designed port.

The use of the above equipment gave us low cost, accuracy, minimum size and minimum power consumption, which was our initial aim.

Software Description

The PIC was programmed in Assemply language. The code that was executed by the PIC had to perform the following tasks :

• Initialisation of the LCD.
• Displaying the information on the LCD and updating the display every minute.
• Decode the signal received from the receiver module.
• Decode the input from the thermometer.

The size of the code had to be minimun for two reasons :

• The memory of the PIC is limited.
• The accomplishment of high execution speed.

Summary

What we have managed to do in our project was the implementation of a stand alone module that is able to synchronise itself with a radio signal coming from the National Physical Laboratory and displays the current time, date and temperature on an LCD panel.

The special features of our clock are that it never needs adjusting, it has the minimum possible power consumption, small in size and its cost is low due to the fact that low cost, but exellent components are used.

After 5 weeks of hard and productive work our group has managed to reach its target. For that we would like to thank our supervisor, Ian Harries, who has been there for us whenever we needed his help, even in the middle of his lunch. We would also like to thank Dave Adams, who was always willing to help us, with any problems that came in our way, and believe me there were many...

Last updated : Thursday, 12th June 1997