Is there a code to check if a PIR sensor is connected?

[arduino_enjoyer45]

Hey people of the forums,

I would like to ask if there is a code that detects if a sensor is connected to the arduino automatically.
For example, I have a DS18B20 that gives a reading of -127.00 if it's not connected, so I placed an if statement saying if it's equal to this, then it's obviously not connected.

Seems simple enough, right? But for a PIR Motion Sensor, I placed an if statement saying if digitalRead equals 1, then it is definitely on. However, I may look silly waving my hand every time the arduino gets reset just for that message of saying it is on.

[groundFungus]

Probably no way without getting the sensor to change state (wave to it), but who can say for sure cause we do not know what exact PIR Motion Sensor that you have. Does it have a data sheet?

[arduino_enjoyer45]

Oh, sorry. Here's the datasheet, it's an el cheapo HC-SR501, which you can only adjust the range and delay through physical means.

31227sc.pdf

[groundFungus]

I have some of those and there is no way to query them that I know of. But, of course, that does not mean that it is impossible. There may be a member that has a clever way to do it.

Edit: I just thought of something to try. Give me a minute to wire up a IR LED and one of my sensors. Maybe turning on (flashing) an IR LED that it can see will get it to change state.

[groundFungus]

I didn't think that it would work and it does not, but we are allowed to experiment, aren't we?

Probably the IR wavelength of the IR LED and human body are that much different. I had no luck finding to what wavelength that the HC-SR501is sensitive. I am pretty sure that my IR LED is 940nm.

[octopirate]

@arduino_enjoyer45

I have a DS18B20 that gives a reading of -127.00 if it's not connected

How can something that's not there, tell you it's not?

[jfjlaros]

Maybe this conversation is relevant?

Check if pin is floating/disconnected/high-z?

So, I have an Arduino mega in an inaccessible location, wired into a series of external components (Radios, Gyros, GPS, Servos etc...) via connectors. Now, I want to program the Arduino so that the system can give me a Boolean value as to whether each pin is connected to anything (+ Voltage or Ground), or whether it is disconnected (i.e. Floating, or as some people call it, high-z). Of course, I could poll each pin to see if it was fluctuating, but this wouldn't work for devices like the Gyro b…

[arduino_enjoyer45]

Not connected as in I ran a code involving ds18b20 but on an Arduino that does not have the ds18b20 sensor. Does that make sense?

It's the same as how I figure out my light sensor isn't connected - the pin gives a value of -2.00.

[PaulRB]

Maybe connect a high value pull-down resistor like 470K to the Arduino pin. Start with the pin in INPUT mode. If the pin reads HIGH, the sensor must be connected. Otherwise change the input mode to INPUT_PULLUP. If the input changes from LOW to HIGH, the sensor not connected. Obviously this is not fool proof. All it ready does is detect if the pin is floating. But that might be good enough for this project.

[arduino_enjoyer45]

aw shame it doesn't work, i thought it was a good idea as well.

[arduino_enjoyer45]

I'll give this a try, thanks.

[arduino_enjoyer45]

I don't know, PaulRB, re-reading this again, I don't want the pin to read HIGH all the time, because it is a motion sensor.

[PaulRB]

It will only read high when motion is detected. My suggestion will not prevent it from working.

[gfvalvo]

@PaulRB

It will only read high when motion is detected.

But does the PIR actively pull the output HIGH when motion is detect or is it an Open Collector output?

[anon57585045]

The PIR on the data sheet that was linked to, shows an onboard MCU driving the output through a 1k series resistor.

You could attach it to an analog input and bias it with a high value voltage divider. It would read half scale (or something) when not connected, and some digital level when connected. You don't need the bandwidth of digital for this.

[PaulRB]

@gfvalvo

does the PIR actively pull the output HIGH when motion is detect or is it an Open Collector output?

Not certain about that, I admit, and my suggestion relies on the sensor actively pulling HIGH/LOW. The data sheet may say something about that in its original Chinese version, but the English translation reads like it was written by a drunken idiot.

[tepalia02]

It's possible to detect motion by reading the pin. But there is no way to check if the sensor is connected.

[J-M-L]

easy: connect a camera, write a small ML based image recognition software that detects when the sensor is correctly connected

[dlloyd]

With a spare sensorCheckPin and a 10K resistor connected from it to the sensorPin, you could see if you you can pull the sensorPin both high and low.

• If the sensorPin status follows the sensorCheckPin output status, then the sensor is disconnected.
• If the sensorPin is stuck high or stuck low, the sensor is connected.

Just change the checkSensorPin back to input after the test.