Mikrokontrollerid ja robootika kodutöö 3 (0)

Question 1

Name 9 characteristic parameters of sensors .
Treshold, noise, range, stability, linearity, accuracy , precision, sensitivity , hysteresis

Question 2

Given the circuit below (using a SYH-2R humidity sensor ) determine the output voltage for a relative humidity of 70 % at 30 °C if RT = 50 kΩ and VDD= 2.5 V.
= 0,388 V
Hint : Check specification for Humidity Sensor of SYH-2R.pdf at
http://www.rhopointcomponents.com/images/SYH-2R.pdf
2 Week 04 Homework

Question 3

Given the following bridge circuit for a strain gauge, determine the value of the strain gauge resistanceLet: VIN = 5V
R3 = 200 Ω R2 = 50 Ω R1 = 100 Ω

Under no strain (VOUT = 0 V)

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Week 04 Homework 3

Question 4

You want to measure temperature ranging from -10 °C to 50 °C using a negative temperature coefficient (NTC) thermistor. You are using the circuit given below.
V  V
(1 RF

• RF )  VRRF
  

OUT Sensor
RL RH RH

Draw the resistance-temperature characteristic for the thermistor over the specified operating range.

Assume VR = 5V. You are designing for a measurement accuracy of
±0.5°C.
What is the minimum value that R1 can assume? Use a safety factor of 2 and assume the Dissipation Constant (D.C.) of this thermistor is 1mw/°C.
P = 1mW/C * 0,5C = 0,5 mW  P = 0,5 / 2 = 0,25 mW (safety factor = 2)
R = 5758 Ω
Current through thermistor : 1,2/5758 = 208µA
Voltage needed in pullup : 5-1,2 = 3,8V
Resistance needed in pullup : 3,8/208 = 18,3 kΩ
kΩ

Assume R1 is selected as 22 kΩ. Plot the output voltage VO against temperature.

Plot the thermistor power dissipation against temperature.

The output at VO is connected to an 8-bit ADC with reference voltage of 5 V. Design RF, RH and RL for optimal temperature resolution. Use the range
0.5 – 4.5 V as in Ball Chapter 3.
Since we have 8 bit = 256 step resolutions
-10°C corresponds to
50°C corresponds to
3.35/5 *256 = 171
1.02/5 * 256 = 52
8 bit ADC steps of 171-52=119 counts for 50C to -10C = 60C span
Therefore, the resolution is
steps
We want the -10°C to 50°C falling between 0.5V to 4.5V on the ADC: This caling will give 8bit ADC range of 204 counts over 60C span.
Before scaling, the output V0 span is 3.35V-1.02V=2.33V. After scaling, the output V0 span will be 4.5V-0.5V=4.0V.
The gain (amplification) for this will be
4 / 2.33 =1.7
The outputs will be : 3.35V* 1.7 = 5,7V and 1,02v * 1.7 = 1,73
The offset will be 1.73V -0.5V = 1.23V
VR= 5 V and RF= 10kΩ
RH = kΩ
kΩ

What is the temperature resolution that could have been achieved without scaling?
Before scaling : 1.98 steps/ C.
After scaling : 3.4 steps/ C.