Temperature Projects:Digital Thermometer With High and Low Alarm Outputs

PROJECT 20 – Digital Thermometer With High and Low Alarm Outputs

Function

This project is similar to Project I9 except that the DSI620 is programmed so that a buzzer connected to the TCOM output of DSI620 turns on when the temperature is equal to or greater than TH and it then turns off only when the temperature drops below or equal to TL. In this project, TL is set to 25oC and TH is set to30oC.

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Circuit Diagram

The circuit diagram of this project is same as in Fig. 5.8 except that the MOSFET transistor is connected to pin 5 (TCOM) of the DSI620 instead of pin 7 (see block diagram, Fig. 5.I0). A small buzzer is connected to the TCOM output of the DSI620 via a MOSFET power transistor. Normally the TCOM output is at logic low level and this output goes to logic high when the temperature exceeds the value TH (stored in the non-volatile memory of the DSI620) and then goes back to logic low when the temperature is equal to or less than TL.

Program Description

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The program is basically the same the as the one in Project I9 except that the temperature high limit (TH) is set to 60 so that THIGH output goes high when the temperature is equal to or exceeds 30oC and TL is set to50 sothat the TCOM output goes back to 0 when the temperature drops to 25oC or below, i.e. the buzzer will turn on when the temperature reaches 30oC and it will go off only when the temperature drops to 25oC or below.

Program Listing

The full program listing is shown in Fig. 5.II. This listing is the same as the listing in Project I9 with the addition of a function called set_tlow which sets the low limit (TL) of the DSI620.

Required Components

This project uses the same components as in Project I9.

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