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Topic: Can two arduino's share the same sensor? (Read 292 times) previous topic - next topic

josephchrzempiec

Hello i was wondering if 2 arduino's sych as the Uno boards can share the same sensor such as a LM35 temperature sensor or the DHT11 sensor?

robtillaart

in theory yes with additional electronics that does some switching, maybe even without (for the DHT11) if you have some really tricky (clever?) scheme.

but it will be much easier and robust to make one A. the owner of the sensor and just send the measurements to the other A.  e.g. over Serial.

Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

josephchrzempiec

#2
Dec 31, 2014, 11:53 am Last Edit: Dec 31, 2014, 12:01 pm by josephchrzempiec
Hello well it's just a idea i have for a future project to have a dual redundant arduino to share the same sensors yeah i know its a little over kill lol. but no clever scheme there.

My current project is i have 2 arduinos talking to each other in i2c a master and a slave node.  The master is telling the slave node to turn on and off leds. this is what i found online. i have another post in here recently on this topic of programing I'm trying to get the slave arduino to have the temp sensors on it and the master arduino display the data it gets from the slave through the i2c. the other one i posted is just a future project thinking about.


Joseph

robtillaart

I2C is a good way to share measurements.
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

josephchrzempiec

Well i do know how to do it on one arduino but I'm not sure how to process it from one arduino and have the other arduino display it on a serial monitor or lcd yet over the i2c.

robtillaart

#5
Dec 31, 2014, 02:38 pm Last Edit: Dec 31, 2014, 02:38 pm by robtillaart
just ask the slave for a measurement
e.g. requestFrom(ID, 8 ) to get 2 floats (packed as bytes) .
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

mrburnette

Hello well it's just a idea i have for a future project to have a dual redundant arduino to share the same sensors yeah i know its a little over kill lol. but no clever scheme there.
<...>
IMO, if you want redundancy, use a sensor and $3 Pro Mini for each node and then route the output to a master uC which would analyze and sanitize the sensor+uC combo... taking an average if both are working or logically removing one from the calculation if the determination is made that a sensor+uC pair is malfunctioning or giving erratic readings.  Sensors are more likely to fail than the uC - again IMO... so, creating pairs for redundancy is a better engineering design.


Ray

Paul__B

#7
Dec 31, 2014, 10:57 pm Last Edit: Dec 31, 2014, 10:58 pm by Paul__B Reason: Emphasis
Rats!  Someone else got in first while I was watching the fireworks!  And went to bed soon after.

Yes - clearly if you want redundancy, you must use two sensors as well as two Pro Minis.

mrburnette

Rats!  Someone else got in first while I was watching the fireworks!  And went to bed soon after.

Yes - clearly if you want redundancy, you must use two sensors as well as two Pro Minis.
GeeWhiz Paul__B ... did not know we were racing!  Happy New Year.
Ray

Paul__B

Is there not some kudos (not to be confused with Karma) to being the first to concisely state the blindingly obvious?

josephchrzempiec

hello that is actually what i was thinking i do have some pro minis i was thinking of using thank you. iwas thinkig if there was going to be a problem of 2 arduino's sharing the same sensor. but i guess it will work. thanks i think i got the all the details of ut worked out.

scrumfled

You could always buffer the sensor outputs with a unity gain op-amp. that'd give you a crude form of isolation (obviously need to check any impedance requirements of the source).

Paul__B

You could always buffer the sensor outputs with a unity gain op-amp. that'd give you a crude form of isolation (obviously need to check any impedance requirements of the source).
Hmmm.  LM35 OK, but do you know what a DHT11 is?

DrAzzy

DHT11 is sharable with only software considerations (you want to make sure the other uC isn't talking to the DHT before attempting to get data from it), and for short runs, analog sensors can also be shared with ease.

As others have pointed out, though, this would be nonsensical to do if we want redundancy, because the sensors are more likely to fail than the uC. Particularly the DHT's - absolutely no quality control!
Please don't PM me questions or responses to my posts. I am unlikely to see or read them.

josephchrzempiec

DHT11 is a Temperature/Hudmity Sensor together. http://www.ebay.com/itm/DHT11-DHT-11-Digital-Temperature-and-Humidity-Sensor-Temperature-sensor-Arduino-/400489574221?pt=LH_DefaultDomain_0&hash=item5d3f09ef4d

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