Temperature control - Humidity Sensor

Dear All,

I am a beginner here. I want to make a temperature control using Arduino. Also i need a humidity sensor. I found that DTH11 will do both.

But I also need the temperature to be controlled only through Thermocouple & resistance due to experimental restrictions.

Can anyone suggest me if it is possible to connect a thermocouple and resistance to arduino?

Regards Pushpa

Hello

The answer to both is yes.....

Do you mean a resistance thermometer? For example a platinum resistance thermometer? A PT100 thermometer has a known resistance at a set temperature e.g. a PT100 has a base resistance of 100 Ohms at 25 degrees Celsius or whatever - I can't remember exactly what it is - then there will be a coefficient of change in resistance with temperature. You would need to look these up. By passing a known current through the PT100 you can pick off a voltage, then use the voltage as an analogue input to Arduino. You could use a bit of Nichrome wire, but you would have to do the calibration.

There will be plenty of examples on how to do this.

Platinum resistance thermometry is the gold standard for industrial temperature measurements and I used them a lot, generally on a 4-20mA loop. The downside is that they are expensive. The output is generally linear. They come in 2-wire, 3-wire and 4-wire versions - the 3 and 4-wire versions allow you to compensate for lead resistance.

Thermocouples are also popular and come in many different types and temperature ranges. The biggest problem is that they have complex outputs that are not linear. Plus there are problems when you introduce new junctions i.e. Fe(iron) to copper. Again, widely used in industry, but generally with a thermocouple amplifier to do the hard work. They sometimes need a "cold junction"

If you want wide range accuracy, I would avoid thermocouples

There is a wide choice of alternative IC devices (analogue LM35, digital like Dallas DS18B20) all with pro's and con's. If you have to go down the resistance/thermocouple route then I would find some IC's to do the signal conditioning or you are going to end up with a lot of software maths

Thanks Tigger!

I should really understand many things before I start with.

How much do you think is the starter kit going to help me, if am a novice?

Hello

I you really are starting from scratch, you need to get the very basics going first.

Are you talking about the Arduino starter kit? The kit used to come with a thermistor which works a bit like the platinum resistor, but again. these are non-linear - look up Steinhart–Hart equation.

Get a simple temperature sensor like LM35 or the newer TMP36 - 50-cents. Nice easy analogue to work with, loads of examples (Sparkfun, Hobbytronics) - use that as an analogue input.

Design your sketch to take the temperature readings and make decisions (if...) what to do if the temperature goes under or over the set point (the temperature you want to reach) - look up hysteresis for better control. Set a digital pin to output and you are away. Stick an LED on the pin to see if it's working, but for bigger loads, use a transistor to drive relays etc. BEWARE anything to do with mains power.

There are loads of examples out there or get a copy of Arduino Cookbook or Jeremy Blum's book for thermostat and display examples.

You need to tell us why you have to use thermocouples etc. - you could be making a rod for your back.

PS make sure you know what the output is from your proposed humidity/temperature sensor - some are analogue, some are digital - digital is a whole new ball game, but once mastered, you won't look back.

Thanks Tigger!

I am a s/w engr moving to mechatronics. So I may sound crazy with no much ideas here. All I heard about Arduino is through my friend seeing some website, about humidity/temp sensor which uses Arduino DTH11.

But let me tell you what I am supposed to.

I need to measure 1. humidity
2. measure & control temperature. I need to have some 50 deg in my set up. For that I need to use a resistance/thermocouple combo to be effective.
3. I need to automate this on a computer software, mostly using LabView.

Now please tell me, what should I start with? If am a novice, I think I’ll first get a starter kit to practice with. Then how to go with my requirement?

I am not sure if my choice for DTH11 was right?

Hello Pushpa

You are trying to run before you can walk. Arduino is an easy to use MCU(microcontroller unit) based on ATMEL chips. If you are serious about this, you need to get an Arduino Uno Rev 3 or a Uno starter kit. The Uno will easily do what you want to do - MCU's are designed to take inputs like temperature sensors or any sensor, do some maths like scaling and timing and then do outputs to control LED's, relays, anything you like - with the right scaling and enough Arduinos, you could run a nuclear power station.

This Arduino site will give you all the information you need to get started - read the getting started bit.

You still haven't said why you need thermocouple/resistance what? These are not good choices to start with.

Your questions

1) Humidity - get an analogue sensor to start with (Honeywell HIH-4000) 2) Temperature - get an analogue sensor to start with (thermistor, LM35, TMP36) - these are all good for 50-C, but don't push it too much higher. Thermocouples are designed for much higher temperatures like ovens and furnaces. 3) LabView? Steady on - it can be done, but get your Arduino to work first - remember this is an Arduino site, not LabView. Maybe you don't need Arduino at all. DTH11? Get hold of the data sheet and read the spec - if it runs on 5-V and puts out a voltage output, then it would be OK

If you are patient and prepared to do the groundwork, you will get a good grounding in MCU's, BUT it's a huge subject.

Good luck