I would like to check the status of the sensors with Arduino UNO. For example, when I turn on the robot, I would like to check if all the sensors are connected and ready to be read or not. Maybe one sensor is unplugged and I want to detect this situation.

I read something about pull up resistors, but I didn't find any clear example of my problem. Also, I don't have any idea how to connect the resistor, how to calculate the resistor needed, as well as how to use the pull up resistor for digital and analog sensors.

Any schema, explanations and example would be very helpful!

  • Depends what kind of sensor. There is a a plain analogue pin connection, digital connection via spi or i2c.... Be a bit more specific. – Miro Krsjak Jan 16 '17 at 17:51
  • the i2c scan sketch comes to mind, at least for that bus. you don't have to run it as a whole sketch; the code within shows how to iterate the devices on the bus, which can be called from a startup routine or whatnot... – dandavis Sep 25 '17 at 21:32

Basically pull-up resistor pulls up the line, when nobody/nothing is doing otherwise (for example wire unconnected, or connected to INPUT, or to I2C bus, which is not doing something right now ...). If some device (or Arduino) sets the wire to LOW (0V, GND, ground), the it overrules the resistor and the wire is LOW.

So the value of the resistor must be high enought to anable any attached device to draw the wire LOW. So if you know, how much of current can a device sink and what is considered LOW value on input, then you can compute the minimal value of the resistor from Ohm law (and the Vcc, where the resistor is connected). If you do not want calculate anything, just put 10KOhm between the wire and Vcc and it would probabelly work just fine.

About detecting sensor - you have to know, what sensor and where is supposed to be attached (as you construct the robot). So you just send any command to the sensor (probabelly to read a value) and see, if you get answer and the answer make a sense (eg. temperature is like 0-100 Celcius, or so). If it works OK, then the sensor is connected and can be used, otherwise you should stop the robot, light big red light and wait for user to repair what is broken. Thing also about the type of sensor, if it needs some time to "boot up" and it it needs some time to "seatle the value and answer" to provide that time before testing (like with delay()).

The pull-up resistors fits there in the way, that they are connected to Arduino, so if there is no connection to sensor, then the unconnected pin is not "floating" (and possibly return any random or not random value), but is weakly drawn up ti HIGH, so if the connetor is broken/unattached, then all reads are just plain HIGH, no communication from sensor (or any noise to be messing with the detection). So you can detect "no answer" status and after a while (when sensor really, really should answer, but did not) flash that big red light.

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