Electronics notes/Temperature sensing

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This is for beginners and very much by a beginner / hobbyist.

It's intended to get an intuitive overview for hobbyist needs. It may get you started, but to be able to do anything remotely clever, follow a proper course or read a good book.


Some basics and reference: Volts, amps, energy, power · batteries · resistors · transistors · fuses · diodes · capacitors · inductors and transformers · ground

Slightly less basic: amplifier notes · varistors · changing voltage · baluns · frequency generation · Transmission lines · skin effect


And some more applied stuff:

IO: Input and output pins · wired local IO · wired local-ish IO · ·  Various wireless · 802.11 (WiFi) · cell phone

Sensors: General sensor notes, voltage and current sensing · Knobs and dials · Pressure sensing · Temperature sensing · humidity sensing · Light sensing · Movement sensing · Capacitive sensing · Touch screen notes

Actuators: General actuator notes, circuit protection · Motors and servos · Solenoids

Noise stuff: Stray signals and noise · sound-related noise names · electronic non-coupled noise names · electronic coupled noise · ground loop · strategies to avoid coupled noise · Sampling, reproduction, and transmission distortions

Audio notes: See avnotes


Platform specific

Arduino and AVR notes · (Ethernet)
Microcontroller and computer platforms ··· ESP series notes · STM32 series notes


Less sorted: Ground · device voltage and impedance (+ audio-specific) · electricity and humans · power supply considerations · Common terms, useful basics, soldering · landline phones · pulse modulation · signal reflection · Project boxes · resource metering · SDR · PLL · vacuum tubes · Multimeter notes Unsorted stuff

Some stuff I've messed with: Avrusb500v2 · GPS · Hilo GPRS · JY-MCU · DMX · Thermal printer ·

See also Category:Electronics.

This article/section is a stub — probably a pile of half-sorted notes and is probably a first version, is not well-checked, so may have incorrect bits. (Feel free to ignore, or tell me)

Thermocouple

Inexpensive

High range of temperature

Produce voltage due to the thermoelectric effect - on the order of millivolts so most uses, and accurate use requires amplification (with high input impedance to avoid the measurement affecting the thermocouple itself).

These age with time and high-temperature use, so will need occasional recalibration and/or replacement.


Thermocouples are any two metals (typically alloys) touching, so in theory there are endless variations.

There are some combinations that became industry standards, and specified.

Not highly accurate - assume you won't get better than 1 degree Celcius of resolution, less if you don't calibrate well, and also varying somewhat with type.


The most common in general use may be type K.



https://en.wikipedia.org/wiki/Thermocouple#Types

Thermistor

Most resistors vary their resistance with temperature.

A thermistor (thermal resistor) does it intentionally, and more pronounced.


NTC: negative temperature coefficient, resistance drops (logarithmically) as its body temperature increases

PTC: positive temperature coefficient,


The 'at-rest' resistance varies with intent


They are frequently used in temperature sensing, temperature regulation, and (over)current protection.


Perhaps the he simplest way to get a voltage from a thermistor (think ADC, comparator) is to have it be one leg of a voltage divider.



Power thermistor

A power thermistor is a very low-resistance (NTC) thermistor in series with your main current, as a current limiter and/or (self-resetting) overcurrent protector.


One use is to spread the inrush current (in transformers and such) over more time:

  • place in series with the primarily coil
  • when cold (just switched on) it typically has a few hundred ohm resistance
  • and once it warms it (few seconds later) goes to under an ohm.

This lessens the magnitude of the sudden current that can happen right after you switch something on.


See also:

Diodes

The voltage across a diode will decrease by approx 2 mV per °C in a fairly linear way.

Accuracy isn't great and you need amplification, and probably a DAC if you want in digital form, but it's quite convenient inside processors, FPGAs, and such.

Unsorted

DS18B20

This article/section is a stub — probably a pile of half-sorted notes and is probably a first version, is not well-checked, so may have incorrect bits. (Feel free to ignore, or tell me)
1-wire interface
range: -55°C to 125°C (seems quoted both as sense range and operating range)
accuracy:
see also DS18B20 accuracy curve, and things like this evaluation/calibration)
quoted as
0.5°C within -10 to +85°C
up to 1 or 2°C in the -10..-55°C and +85..+125°C ranges
e.g. in a quick test of two of mine on wet ice cubes, the two settled on 0.44C and 0.19C, and in boiling water went up to 99.13C and 99.44C, respectively.
And that's one one that appears to be counterfeit (apparently one of the better ones)
there are counterfeits with clearly less accuracy (many cheap ebay/aliexpress will probably be this[1]
you can do some custom calibration, with a distilled-water ice bath, boiling water
drifts a few tenths of a degree
sample speed is 100ms..750ms depending on resolution
3V ~ 5V supply


By itself it's a through-hole TO-92 part.

Waterproof enclosures are moderately common, often in stainless steel, and preferably (but not always) with silicone cable, so you could actually stick it in a sauna (particularly if you poke it through a wall).


On the resistor

1-wire needs the data line to be pulled high, so that the master and (potentially multiple) devices can each pull it down. (and, in some cases, for parasitic power, but for this sensor we'll probably not use that)

It's common practice to add a 4.7k resistor to Vcc (varying a little with what that voltage is).


And yes, you can also use a microcontroller's internal pullup. They're typically rather higher value (e.g. 50k) so for longer wires the capacitance involved means communication may break down - but for short wires it works fine.

[2] [3]



On counterfeits:

This is a whole bunch of research.

tl;dr

  • some behave differently
  • some have more noise on the measurement
  • some have a few degrees of error (worse than a cheap DHT11)
  • some are poorly calibrated, but would be fine with two-point calibration by you
  • some are basically fine -- but you won't know which knockoff you'll get.



See also

DHT11, DHT22

Measures:

  • Temperature (NTC thermistor)
0-50 ℃
output reported to 1℃ but don't assume more than ±2℃ accuracy
  • Relative Humidity
Range: 20 to 90 %RH (note: range and accuracy vary somewhat with temperature)
output reported to 1% but don't assume more than ±5%RH accuracy


In a quick test with two DHT11 modules next to each other, temperature was reported 0.0 to 1.0 degrees apart on average, but humidity was ~11 %RH apart on average (fairly consistently so you can probably improve this a little via calibration against a known value).


Pins: 3.5-5.5V, data, NC, Gnd.

You will want a pullup resistor on the data pin, mostly because it's bidirectional onewireish(verify).

Power: ~0.5mA while measuring, 0.1mA idle


DHT22:

RH: 0 to 100% range, 2 to 5% accuracy
Temp: -40 to 80°C range, ±0.5°C accuracy



HDC1000

https://www.ti.com/lit/ds/symlink/hdc1000.pdf


HDC1080

http://www.ti.com/lit/ds/symlink/hdc1080.pdf

LM92

http://www.ti.com/lit/ds/symlink/lm92.pdf


BMP085

https://www.sparkfun.com/datasheets/Components/General/BST-BMP085-DS000-05.pdf

https://www.sparkfun.com/tutorials/253

BME680

https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bme680-ds001.pdf


BME280

Humidity and pressure sensor

https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bme280-ds002.pdf


BMP280

Pressure (also temperature)

https://www.bosch-sensortec.com/products/environmental-sensors/pressure-sensors/bmp280/

AM2320

https://akizukidenshi.com/download/ds/aosong/AM2320.pdf

See also

http://www.electronics-tutorials.ws/io/io_3.html