ELECTRONIC THERMOMETER CIRCUIT

NAME: OĞUZ

SURNAME: GENÇER

UNIVERSITY: ESKİŞEHİR OSMANGAZİ UNIVERSITY

STUDENT NUMBER: 151220072067

What is important in this Project?

As the people know, the temperature control is so important in many field. We are living under some conditional boundary values like temperature, pressure and maybe the time is under this condition too. Anyway, so we have to know measure this values usually, at least to satisfaction our curiosity.

The Component List

Component Name Quantity The unit price (TL)LM3914 3 3,25 TLLM35DZ 1 3 TLGreen Led 10 0.1 TLYellow Led 10 0.1 TLRed Led 10 0.1 TL2.2uF Capacitor 3 0.25 TL1uF Capacitor 1 0.1 TL100nF Capacitor 1 0.1 TL100uF Capacitor 1 0.25 TL1Kohm Potentiometer 4 0.5 TL75ohm Resistor 1 0.1 TL330ohm Resistor 1 0.1 TL2.2Kohm Resistor 3 0.1 TLEpoxy plate (20x20)cm2 6 TLDrill bit 1 1.5 TL

How the circuit works?

In shortly, this circuit can measure the temperature and display us the temperature value in the place where we use it. There are 2 teqhniques to measure the temperature; to measure by using digital signals or to measure by analog signals. Both of them are being used in the life. But I have choosed the analog one. So I used a LM35 series component. This component produce voltage in mV level when the temperature goes up. LM35 is work between -550C and 1500C but I made the circuit for more specific values also I used LM35DZ whose range is between 00C and 1000C.LM35DZ produce 10mV on its output for each 10C. To drive the led displays, I used a LM3914 Dot/Bar Display driver component. This component can drive 10 leds like dot or like bargraph. It changes with the mode settings which is included in LM3914 datasheet. I used the bargraph mode because I want to see when all leds lighting until the last led which shows the temp value. There are some different methods to make voltage divider in the input of LM3914 I used some of one in my circuit. And I choosed the component values which is the same with in the datasheet example. I use this circuit with the range of 100C to 400 . First 10 green Led displays us the range of

100C to 190C and next 10 yellow Led displays us the range of 200C to 290C and the last 10 red Led displays us the range of 300C to 390C. These boundaries can set with chance the potentiometer value. We must to set up the 4th pin of first LM3914 to starting value of the range. (10mV x 0C) this formula can be used for determine the range values; 4th pin of 1st LM3914 is: (10mV x [(0C)-1]) = A mV6th pin of 1st LM3914 is: A + (10mV x 0C) = B mV6th pin of 2nd LM3914 is: B + (10mV x 0C) = C mV6th pin of 3th LM3914 is: C + (10mV x 0C) = D mV

I chose the first range as 100C to 190C so I calculated;

A = [(10-1)0C x 10mV] = 90mV

I chose all range as 100C so; B=190mV

C=290mV D=390mV

As measure that points by using a voltmeter and after your calibration the circuit you can set the circuit as how you want it works.

How can make a PCB design and producing?

In my project I used a computer based electronic circuit design program(Proteus).There are many program like this you can use anyone of them too. I made first shematic circuit and convert it to PCB in Proteus. I wanted to make a thermometer with a circular shape so I placed components as I wish. You can do your circuit too as you wish.

When you finish the design of PCB circuit, you can print out the design to a glossy paper or an acetate from a Laserjet printer on the boldest mode. There are some pictures below I had them when I was making the circuit. Now you need an heating iron for transer the circuit design to the epoxy plate. Firstly, you must paste your printed out papper to the epoxy plate. If you don’t, your design will be transfered but it will be slided and maybe there will be some short-circuit in your epoxy plate. I use the iron in cotton heating level and putting a slim cotton swab on epoxy

plate.You can do this or something else. Its only for better result on transferring. After that you can start to ironing and you can plug in your iron. Its enough to ironing 3-5 min. Later you must shock your epoxy plate. For this you can put it in a freezer or you can wash it with cold water. 1 min is enoug for this prosses. When you have a printed out and transferred design on epoxy plate, you can prepare the chemical solution now. There are many chemical solution formula. I have chosen 1 measure of H2O2 for 4 measure of HCl. After preparing the solution, we can put it in a pot and put the epoxy plate in it. Make some wave on solution and approximately 1 min later your cicuit will be ready. Dont take it from solution if you see any copper layer yet. And be careful when you take it from solution. Then you can wash it. After washing I used some powder detergent and wash the epoxy plate with it.

Now we can drill the pads and make some holes. After the drilling we can put the components on their places. Then we can start to soldering. I prefer to soldering from chip sockets. Then I started to soldering from center toward outer. You can do it as you wish. After soldering the circuit you can finally start to work with it.

What I have learned from this circuit?

I use LM3914, LM35DZ, potentiometer some electronical component. I learned how this components works. I can easily make another circuits with them. It was a good experiment for learning analog measurement.