# Essay about A Thermistor for Measuring Temperature in Bath Water

Length: 1603 words (4.6 double-spaced pages)

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Instead of having 3 LED’s as the visual output, and alternative would be to use a seven segment display to show a number telling you when a certain temperature is reached. The advantage of this is you can have more than 3 indicators, so you could have different numbers show depending on what age the person having a bath is. For example you would wait for a lower number to show if it’s a baby. The disadvantage of using a seven segment display as the visual output is it isn’t simple enough, when you have a bath you don’t need it at an exact temperature so just having 3 LED’s that light up when the temperature is in that range is enough to tell you if it too hot or too cold.

(g)
For my final solution I decided to use a thermistor to measure the temperature of the bath water, with op-amps as comparators, and 3 different colours of LED’s as an output. Using a LM 35DZ as the temperature sensor would have cost more and being more precise and accurate isn’t needed in measuring bath water temperature. Using logic gates will use up more power and more room because you need more chips. Using seven segment display isn’t simple enough for just telling someone if the bath is the right temperature.

Circuit

Section B - System Development
(a)

Subsystem 1 (Input: Resistor + Thermistor) Subsystem 2 (Process: Op-Amps) Subsystem 3 (Output: LED’s)

(b)
Component Calculation 1 – Protective Resistor Value
The subsystem for this calculation is subsystem 3 (output).
The equation I will use is
Red LED

(E24 Series)
Green LED

(E24 Series)
Blue LED

(E24 Series)

(c)
Subsystem 1: Vout and Current
On the first subsystem I measured the voltage at the points that will be going to the op-amp. On the first subsystem I me...

... middle of paper ...

...otentiometer until the circuit was working, then took it out and measured the resistance, which was 4.79kΩ, I then got a resistor you can fine tune with a screw driver and set it to the same as what the potentiometer was.

Retest Results
LED Expected (°C) Actual (°C)
Blue 35.5 35
Green 38 38.2
Red 42 42.3

The results show the modification has been successful because the values are closer to the expected values and they won’t change if you accidently twist the potentiometer, because you can only change the resistance with a screw driver.

Works Cited

http://www.netdoctor.co.uk/healthy-living/parenting/baby-bath.htm
http://www.rapidonline.com/pdf/56-0430.pdf
http://www.rapidonline.com/pdf/56-0435.pdf
http://www.rapidonline.com/pdf/55-1810.pdf
http://m.netdoctor.co.uk/childrens-health/baby-bath.htm

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