372 Datasheet 372 | P4-P6

On the other hand, they require a little more work to interpret readings, and they dont work at

very high temperatures like thermocouples. Without a digital-to-analog converter on board, you

might be better off with a digital temperature sensor.

Their simplicity makes them incredibly popular for basic temperature feedback control. For

example, lets say you wanted to have a fan that turns on when the temperature gets high. You

could use a microcontroller, a digital sensor, and have that control the relay. Or you could use

the thermistor to feed the base of a transistor, as the temperature rises, the resistance goes

down, feeding more current into the transistor until it turns on. (This is a rough idea, you would

need a few more components to make it work)

Even if you do use a microcontroller or complex system, for the price you can't beat 'em!

You can pick up a 10K 1% waterpro of thermisto r in the Adafruit

shop (http://adafru.it/372)

Some Stats

Here are technical details for the thermistor in our shop (http://adafru.it/372)

Resistance at 25°C: 10K ±1%

B25/50: 3950 ±1%

Thermal time constant ? 15 seconds

Thermistor temperature range -55°C to 125°C

Wire temperature range -55°C to 105°C

28 AWG PVC Wire

Diameter: 3.5mm/0.13in

Length: 18in/45cm

Resistance/Temperature table (http://adafru.it/aK4)

Note that even though the thermistor can go up to 125°C the cable itself maxes out at 105°C

so this thermistor is not good for measuring very very hot liquids

Industries

http://learn.adafruit.com/thermistor Page 4 of 13

Testing a Thermistor

Because thermistors are simply resistors, its easy to test it out. Simply measure the resistance

using a multimeter:

You should read about 10Kohm assuming its room temperature where you're sitting. The

resistance of course may be higher or lower depending on the room temperature. For example,

its warm here in an un-airconditioned room in the middle of the summer, so we read 8Kohm

(30°C - 86°F!)

Industries

http://learn.adafruit.com/thermistor Page 5 of 13

Using a Thermistor

Connecting to a Thermistor

These thermistors are pretty hardy, you can strip the PVC insulation and stick the wires into a

breadboard or solder to them directly. Of course you can cut or extend the wires. Since the

resistance is pretty high (10Kohm) the wire resistance won't make a huge difference.

Analog Voltage Reading Method

To measure the temperature, we need to measure the resistance. However, a microcontroller

does not have a resistance-meter built in. Instead, it only has a voltage reader known as a

analog-digital-converter. So what we have to do is convert the resistance into a voltage, and

we'll do that by adding another resistor and connecting them in series. Now you just measure

the voltage in the middle, as the resistance changes, the voltage changes too, according to the

simple voltage-divider equation. We just need to keep one resistor fixed

Say the fixed resistor is 10K and the variable resistor is called R - the voltage output (Vo) is:

Vo = R / (R + 10K) * Vcc

Where Vcc is the power supply voltage (3.3V or 5V)

Now we want to connect it up to a microcontroller. Remember that when you measure a

voltage (Vi) into an Arduino ADC, you'll get a number.

ADC value = Vi * 1023 / Vcc

Industries

http://learn.adafruit.com/thermistor Page 6 of 13

P1-P3 P4-P6 P7-P9 P10-P12 P13-P13

372

Mfr. #:

Buy 372

Manufacturer:

Keystone Electronics

Description:

Standoffs & Spacers 1.5 Rnd Clr Hle Spcr .250 OD #6 Phenolic

Lifecycle:

New from this manufacturer.

Delivery:

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