Digital Temperature Controller CircuitA Digital temperature controller circuit is a precise temperature controller in medical, industrial and home applications. This system is better than analogue/thermostat system, which has poor accuracy. For example, it can use for temperature control of an incubator where maintaining a precise temperature is very important.Digital Temperature Control SystemDigital Temperature Controller Block Diagram DescriptionThis proposed Digital temperature controller system provides the temperature information on a display and, when the temperature exceeds the set point, then the load (i.e. Heater) switches OFF. In this project, a lamp is provided as a load for demonstration purpose. The Block Diagram of Digital Temperature Control System is given below. Block Diagram of Digital Temperature ControllerThe proposed Digital temperature controller system uses a Microcontroller of 8051 family, which is the heart of the application. The display unit consists of four- seven segment display, Temperature sensor and are interfaced to the Microcontroller.The digital temperature sensor interfaced to the Microcontroller for sensing the temperature conditions. This system also provides four push button switches for adjusting the temperature settings.Then the Microcontroller continuously polls the temperature information through a digital temperature sensor and displays over the 7 segment display unit and automatically switches OFF the lamp, when the corresponding temperature exceeds the set point.Hardware RequirementsTransformer (230 – 12 v ac)Voltage regulator (LM 7805)RectifierFilterMicrocontroller (at89s52/at89c51)DS1621 Temperature sensorPush buttons7 segment displayBC547ResistorsCapacitors1N4007RelayMicrocontroller (AT89S52)The Atmel AT89S52 is an 8051 based powerful Microcontroller which provides a highly-flexible and cost-effective solution to many embedded control applications.The AT89S52 provides the following standard features:8K bytes of Flash256 bytes of RAM32 I/O linesWatchdog timerTwo data pointersThree 16-bit timer/countersA six-vector two-level interrupt architectureA full duplex serial portOn-chip oscillator, and clock circuitryThe pin diagram is given below. 8051 MicrocontrollerTemperature Sensor- DS1621A sensor is a device which receives and responds to a signal or stimulus. A sensor can convert the received signal into electrical form only.The Temperature Sensor- DS 1621 provides the following standard features:Measurements require no external componentsMeasures temperatures from -55°C to +125°C in 0.5°C increments (67°F to 257°F in 0.9°F increments)Temperature is read as a 9-bit value (2-byte transfer)Wide power supply range (2.7V to 5.5V)Converts temperature to digital word in less than 1 secondThermostatic settings are user definable and NonvolatileData is read from/written via a 2-wire serial interface (open drain I/O lines)Applications include thermostatic controls, industrial systems, consumer products, thermometers, or any thermal sensitive systemIt is an 8-pin DIP or SO packagePin DescriptionDS1621 Pin DescriptionSDA – 2-Wire Serial Data Input/ OutputSCL – 2-Wire Serial ClockGND – GroundTOUT – Thermostat Output SignalA0 – Chip Address InputA1 – Chip Address InputA2 – Chip Address InputVDD – Power Supply VoltageA functional diagram of the DS1621 is shown in the below figure.DS1621 Functional Block DiagramThe DS1621 provides 9-bit temperature readings, which indicate the temperature of the device. The thermostat output signal (TOUT) is active when the temperature of the device exceeds a user defined temperature (TH).The output remains active until the temperature drops below a user defined temperature TL, allowing for any hysteresis necessary. User defined temperature settings are stored in nonvolatile memory so parts may be programmed prior to insertion in a system.The temperature settings and temperature readings are all communicated to/from the DS1621 from the Microcontroller over a simple 2-wire (I2C) serial interface.Measuring TemperatureThe DS1621 measures the temperature using a band gap based temperature sensor. A delta-sigma analogue to digital converter (ADC) converts the measured temperature into a digital value that is calibrated in °C or °F.The temperature reading is provided in a 9-bit, two’s complement reading by issuing the READ TEMPERATURE command. The data is transmitted through the 2-wire serial interface- MSB first (I2C Serial Communication interface).Basic Seven Segment DisplayThis version is a common anode version. That means that the positive leg of each LED is connected to a common point which is pin 3, Vcc in this case. Each Light Emitting Diode has a negative leg that is connected to one of the pins of the device.7-Segment LED DisplayTo make it work you need to connect pin 3 to 5 volts. Then to make each segment light up, connect the ground pin for that led to ground through a resistor. It can also be used through any Microcontroller port pin in sinking mode for ex. PORT 0 in 8051 series Microcontroller.SoftwareWe used the ‘C’ language to write the application code and compiled using KEIL micro vision (IDE) compiler. After the completion of the software writing, that code will be converted to hexadecimal code in order to drive the Microcontroller. The generated hex code is burnt into the Microcontroller using a suitable programmer.Schematic Diagram Connections Of Digital Temperature ControllerThe power supply of 5v is required to operate the system, connected to the 40 pin of Microcontroller & GND is connected to its 20pin. Pin 1.0 to 1.3 of port 1 is connected to the push buttons. Pins 3.5 to 3.7 of the Microcontroller are connected to 1, 2, 3 pins of temp sensor DS1621 respectively.Digital Temperature Controller Schematic DiagramPin 0.0 to 0.6 of port 0 of Microcontroller is connected to 7 segment display. Pin 2.0 to 2.3 of port 2 of Microcontroller are connected to transistors BC547 of Port 2 of Microcontroller is connected to transistor’s BC547. Pin 2.4 is connected to another transistor BC547 which drives the relay.WorkingThe project uses a digital temperature sensor DS1621 which is interfaced to the Microcontroller. The surface of this 8 pin IC senses the ambient temperature to deliver digital data serially at pin no 1, which is displayed from the Microcontroller by 4 units of 7-segment common anode display all parallel connected to port ‘0’.Four push button switches are being interfaced to Microcontroller with pull-up resistors to help to program the set temperature as desired. The output from Microcontroller at pin 25 drives a transistor which in turn drives a relay which switches ON or OFF the heater for maintaining the temperature.The project, however, uses a lamp in place of the heater for demonstration purposes. The lamp will be normally ON to get switched OFF once the set temperature is reached.Applications of Digital Temperature ControllerThe following are some examples of applications for which particular attention must be given.Outdoor use uses involving potential chemical contamination or electrical interferenceNuclear energy control systems, combustion systems, railroad systems, aviation systemsMedical equipment, amusement machines, vehicles, safety equipment, and installations subject to separate industry or government regulationsSystems, machines, and equipment that could present a risk to life or propertyThus, this is all about Digital temperature controller using a microcontroller. We hope that you have got a better understanding of this concept.Furthermore any queries regarding this concept or microcontroller based projects, please give your feedback by commenting in the comment section below. Here is a question for you, what is the function of 7-segment display? Share This Post: Facebook Twitter Google+ LinkedIn Pinterest Post navigation ‹ Previous Common Collector Amplifier Circuit and Its ApplicationsNext › How to Build A Hybrid Solar Charger And Its Applications Related Content MTech Projects for Electronics and Electrical Engineering 30 Minute Timer with Circuit Diagram Using 555 IC & 7555 IC ATmega16 – Next Generation Microcontroller LabVIEW Projects for Engineering Students 5 CommentsYour temperature controller utilizes the relay output just to simply turn on/turn off the relay output in order to control the output load (a heater for heating / a cooling fan for cooling, etc.) This type of control is called “Bang Bang” for its lousy control. So your statement “For example, it can use for temperature control of an incubator where maintaining a precise temperature is very important” is overstated. Please let me know if you agree or disagree with my comment.ReplyI wont program of this pid temperature controllerReplyHi Manthan We are very sorry to inform you that we don’t have that coding.ReplyHow to Make Flexible AC Transmitter System Using Thyristor Switch ReactanceReplyHi Hamid Milaad Please refer to this topic in our blog once so that you can find the information on this concept.ReplyAdd Comment Cancel replyComment:Name * Email * Website
Your temperature controller utilizes the relay output just to simply turn on/turn off the relay output in order to control the output load (a heater for heating / a cooling fan for cooling, etc.) This type of control is called “Bang Bang” for its lousy control. So your statement “For example, it can use for temperature control of an incubator where maintaining a precise temperature is very important” is overstated. Please let me know if you agree or disagree with my comment.Reply
Hi Hamid Milaad Please refer to this topic in our blog once so that you can find the information on this concept.Reply