1. temperature system wiring
living with the lab
temperature system wiring
ENGR 121
transistor relay power resistor
© 2013 David Hall

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3. analog input 4 (measures voltage across thermistor)
living with the lab
thermistor circuit and program 5V
analog input 4 (measures voltage across thermistor)
10kΩ
thermistor
If you have not done so already
waterproof your thermistor
create the voltage divider circuit shown
enter the sketch below to make sure the thermistor is working
if the soldering irons are busy, then go to the next slide and begin building control circuit
int val = 0; // variable to store circuit output
void setup() {
Serial.begin(9600); // set up the serial display }
void loop() {
val = analogRead(4); // read the 0 to 1023 integer from analog pin 4
Serial.println(val); // print value to serial monitor

4. normally open contacts
living with the lab
temperature control circuit
Build this circuit. Write a sketch that reads the analog input from the thermistor circuit and displays the 0 to 1023 value on your computer monitor. Then, modify the program to make the LED go off when you heat the thermistor up by holding it between your fingers; the LED should come on when the thermistor cools back toward room temperature. That is, include an “if” statement that makes the LED come on when the analog input is less than a number (such as 500, but you’ll need to pick a number that works). This will be very similar to the program that you use to turn on the heater when the temperature drops below the setpoint. This is also one of your homework problems for next time. 5V
analog input
thermistor
10kΩ 5V C B E
Arduino digital pin
1kΩ + -
12VDC power supply
20W
470W
solenoid valve
normally open contacts
heater to be
added later
coil
SPST relay
You can replace the LED and 470Ω resistor with the heather (the 20Ω waterproofed resistor provided by your instructor) after the LED is working well. NEVER have the heater plugged in (or turned on) unless your fishtank is full of water.