PROJECT 19 – Digital Thermometer with High Alarm Output
Function
This project is similar to Project I7 but a buzzer is connected to the THIGH output of the DSI620 thermometer IC, via a MOSFET transistor. When the temperature exceeds a preset value the buzzer turns on and stays on as long as the temperature is above this value. In this project the alarm sounds when the temperature is equal to or greater than 25oC.
Circuit Diagram
The circuit diagram of this project is shown in Fig. 5.8. The DSI620 ther- mometer IC and the TIL3II displays are connected as in Projects I7 and I8. A small buzzer is connected to the THIGH output of the DSI620 via a MOSFET power transistor. Normally the THIGH 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.
Program Description
The program is basically the same as the one in Project I7 except that the temperature high limit (TH) is set to 50 so that the THIGH output goes high when the temperature is equal to or exceeds 25oC and this turns on the buzzer togive a warning sound.
Program Listing
The full program listing is shown in Fig. 5.9. In addition to the program listing of Project I7, a function called set_thigh is added toload the temperature high limit. This function sends protocol number 0I to the DSI620 and then sends the data value 50 toset TH to25oC.
Required Components
In addition to the components used for Project I7, a MOSFET transistor (e.g. VN66AFN) and a small buzzer will be required for this project.
