Bad sensor, good sensor... accurate sensor!

Hello community.

After playing around with the Arduino and it sensors for a while now, I am asking myself if there is any listing of sensors. I mean a test of them. Which are quite accurate and which are 'just to play around with'.

For example I connected once the DHT11, DHT22 and BMP180 on the came Arduino and measured the temperature. Guess... all 3 had different values. I can't remember how much the difference really was, but it was quite different (approx +/- 5 degrees). And I know that there are tons of other temperature sensors for the Arduino.

I don't want to make any business with Arduino and I know that everybody is saying 'hey, its just for playing around and having fun'... but no, I want more then just playing around. I want to use it.

Now I have a bigger project in front of me and want to use the Arduino with its sensors to be my 'helper'. I don't expect 100% accurate results... but as best as possible. I want to use distance sensors that I don't hit the wall. I want temperature, humidity sensors to know what is the weather like. I want light sensors to know if its night or day (cloudy or sunshine). I want gas sensor to know if my gas bottle/pipe/connector is leaking. I want a compass sensor to know in which direction I go. I want a GPS sensor to know where I am and how fast I move. ... etc.

Is there any webpage or list which tested Arduino sensors on reliability and accuracy?

Hope you know what I mean :slight_smile:

Cheers

Good sensors come with decent datasheets which has at least has a graph or table for error% if temperature, voltage or humidity or ... changes.

Some sellers make a selection for good sensors. For example Sparkfun, Pololu, Adafruit.

You want to know the temperature, and you didn't use a DS18B20 :o

This is my list for this moment:

  • BMP085 : 25.58 °C
  • DHT11 : 24 °C
  • DHT22 : 23.4 °C (in the next room, might be cooler)
  • forward voltage of diode with tuned calculation: 24 °C
  • DS18B20 : 24.12 °C

The BMP085 seems to be the most inaccurate. Perhaps the BMP180 is improved. I think the DS18B20 is the most accurate, I have tested one a while ago in freezing and boiling water.
Measuring the real temperature is not always straightforward. For example the DS18B20 seems to collect heat from around, like a little sunlight, or a hot voltage regulator nearby, and the temperature rises a lot.

Good sensors also come with a price. If you want accuracy, you need to pay for it.

eBay specials are for playing with.

Weedpharma

@robtillaart
Also sensors which are not very accurate come with a datasheet. That is not really a criteria.

@Peter_n
It was just an example. But you are right, I didn't knew the DS18B20 yet.
But I am not just talking about temperature sensors. In general.

@weedpharma
That is probably right. But to general. I would like to have a list with all sensors and their accuracy.

I need to buy then now soon and to build the system. Answers like 'they have their price' or 'they come with datasheets' doesn't really help my in making my decision which sensors to get.

With so many sensor types and variable accuracy, there is no list.

Tell us what you want and someone may have information on the type and recommendations on what to get.

Weedpharma

HeAdLeSs:
@robtillaart
Also sensors which are not very accurate come with a datasheet. That is not really a criteria.
...

Yes, but the quality of the datasheet gives a good feeling about the quality of the sensor. Good datasheets discuss the error behaviour of the sensor. If it is not discussed that makes the sensor a "suspect"

FYI, a Swiss comparison (In german
http://playground.boxtec.ch/doku.php/sensors/temp-hum_sensors_compared

You should also add "good programmer...bad programmer", or "good builder...bad builder".
Analogue sensors, read with Arduino's A/D, rely on a good reference voltage.
Default 5volt might not be good enough.
Digital sensors might perform badly when not supplied or decoupled properly.
There are many other gremlins.
Leo..

Ya agree with you. If the sensor has the datasheet and you bought from the trusted sites then it is a good sensor otherwise bad! Arduino sensors list

This is just an advert for a collection of sensors. There is nothing to indicate their accuracy.

Weedpharma

The BMP085 has a temperature sensor purely for temperature-compensation, its absolute
accuracy isn't very important once you have calibrated the pressure sensor. Use the BMP
to measure pressure, not temperature!

Have you looked at parametric search on an electronic supplier's website - that'll give a list of
some of the sensors available, and ignore anything dodgy (a luxury eBay doesn't give you!)

You also need to consider accuracy vs repeatability - if the sensor gives a reading of 20.3 each time you test something that is actually 19.9, you can add/subtract a calibration factor to get the right reading (you never get "exact" - you get what is within the needs of your project). If you have a sensor that reads 19.1, 22.3, 18.2 for the same test conditions - either you have a sensor problem that is very difficult to calibrate for or you have issues with the support circuit (A/D, reference etc.). That is a much more difficult problem to deal with - the one where you get a repeatable reading for the same conditions is easy to calibrate for (that is a good use for eeprom - store your calibration factor there and use it in your calculations to give a reading that is within your measurement tolerance. Take voltage for example - for some people looking at the charging voltage in an automotive situation, 13.7 is sufficient accuracy while for other people they need to know is it 13.700000 or 13.700001. The first requirement is to determine what accuracy you need for a project, then you can go looking for sensors that meet that requirement.

Hi guys, I have ordered pir sensor from ebay and I got it without the retrigger jumper. Does anybody know do I still can use it? I don't wanna fries something.


Thank you

Not a problem.
I always set the "time" pot to minimum (fully anti-clockwise).
And do any delay/retriggering in software.
Leo..