# Central heating system project

Discussion in 'Homework Help' started by JoepvB, Mar 15, 2018.

1. ### JoepvB Thread Starter New Member

Mar 15, 2018
1
0
Hello,
I have gotten an assignment at school to make a heating circuit,
also specified as a closed-loop control system of a temperature controller.
But I'm stuck and don't know how to approach it.

this is the assignment given:
I'll add the datasheet mentioned as attachments
Your assignment is to design and build the control system using an NTC resistor, a comparator, a potmeter, various resistors, and an electronic power switch.
For the heating element we will use a power resistor of 10 Ohms with power rating 3 Watt.
The datasheet for the NTC can be found here. The NTC you have has R/T characteristic 2904.
For the power switch we will use an N-FET STP16NF06 (click for datasheet).
Add a LED (+ resistor) to the output of your controller to check whether the output is switched on or off.

So I hoped that someone could help met out on where to start or to give an example of the circuit asked.

Some other things that are asked are:
• Analyse your actuator: what power source do you need to heat it up to it’s maximum?
• What is the maximum supply voltage for the resistor?
• What is the maximum current through the resistor?
• Is the N-FET able to handle that?
• How can you use a potmeter to generate an appropriate voltage usable as setting?
• Analyse your sensor: find the R value vs T graph of your NTC.
• How can you convert the NTC resistance value to a voltage?
• How do you connect the inputs to your comparator?
• How do you connect the N-FET to the comparator?
• How are you going to supply power to the comparator?
• How do you connect the LED and its series resistor? What is the value for the resistor?

So, summarized in short: is there someone that can help me draw the circuit for this assignment? and I've also added an image of a circuit that was given in the assignment as example.

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2. ### wayneh Expert

Sep 9, 2010
15,512
5,739
A lot of people here could draw this for you but none will. The purpose of your homework is for you to learn this for yourself.

I suggest starting one piece at a time. For instance the indicator LED will require a certain current, maybe 5mA. Learn how to light an LED with 5mA once you are given the voltage. Then move on to the switch and the MOSFET, and so on. Read carefully how comparators work since this is the heart of your circuit. Once you understand it, the rest of the circuit will make more sense.

Folks here will help you past any spots if you’re stuck, but need to see that you’re working on it yourself.

Alec_t likes this.
3. ### Alec_t AAC Fanatic!

Sep 17, 2013
9,173
2,163
Welcome to AAC!
The bullet points in post#1 give you lots of clues.
Before you consider how to assemble various components you need to make sure you understand the purpose and operation of each component.
Think of the circuit design as bridging the gap between the tools/components you have available and the end result you are trying to achieve. How will the properties of each component be used to best advantage in contributing to that end result?