hello, i had a quick question that i'm hoping someone can help me with. i'm using an arduino mega 2560 to make a data acquisition system for my Baja SAE team. im wanting to run a hall effect so i can read rpm and from there calculate the speed of the car along with a few other things. im planning on doing this thru a hall effect sensor. the sensor i have says its draws 150ma, is it safe to use this sensor with the mega or would i need to find a different sensor. the end goal would be using two of these sensors (300ma total) one for the engine RPM and one for wheel RPM to gage the trans ratio at any given time, i also have a temperature probe that i'm using in the project but it only pulls about 1 ma. i've heard you can draw more current depending on the power method from the arduino but just wanted to get some clarity on this. thanks for the help.
I have never seen a Hall sensor that needs any significant amount of current,
but 150 mA seems extreme.
Do you have a link to the data sheet?
If these sensors really take that much current, you can not power one of them from a Mega.
i dont have a data sheet but this is the description from the amazon lisiting, heres the link as well.
Model: NJK-5002C Supply voltage : 5-30VDC; Detection distance :10mm (effective detection distance 0-10mm) ;
Output: NPN three lines Output state normally open (NO)
Thread Diameter: 12MM; thread length: 37MM
Load current: 150MA (no more than)
Detect objects ?metal material ?Product Material: Metal; parts: Copper plastic components; PBT External leads:1.2 m; Output indication: LED (red);
Package Content: 1 x Hall Effect Sensor
Ok, you need a separate power supply for the sensors.
ok thats what i was afraid of. when it comes to powering sensors separately do i need to do anything special or can i literally just tap into the powersource before it goes to the arduino so like this? (5v is actually 9 but this will probably change down the line)
The power source ground must connect to Arduino ground as well as the sensor ground.
The sensors seem to work with 5V, so I would pick a 5V supply and feed the Mega via 5V,
but if you have nothing current consuming attached to the Mega, up to 12V on VIN would work also.
The sensors probably need a pull-up, the internal (quite weak one) can be sufficient.
Be careful when using the power plug or Vin. Powering through Vin or the power jack means that the Arduino and all peripherals that are on the 5V rail are powered by the onboard 5V regulator. The on board 5V regulator is not heat sinked so will supply limited current before it overheats and shuts down. The amount of current depends on the voltage input to Vin or the power jack. The higher the voltage the less current can by supplied. I would use a buck converter to drop the 12V to 5V and connect that to the 5V on the Arduino, bypassing the, weak, 5V regulator. Then the rated current of the DC DC converter is available on the 5V line.
the diagram isnt 100% accurate im just saying the barrel connector goes to arduino with that one since its both ground and power in one connector. and then i power the sensor off the wire coming from the battery and send the ground and data back to the mega.
This means you shouldn't load the sensor more than 150mA, not that it uses 150mA. If lightly loaded it won't need very much current - you can measure this...
thats were im not sure. the actual tag on the sensor is in chinese so i have no idea what it says only that its got a 150ma rating on it, i found it very interesting that a hall effect could draw so much. could i just use a multimeter to determine the current it draws?
Yes, you can measure it on a current setting with the meter inline with the supply to the sensor.
The 150mA is the rating of the open collector output NPN transistor in the sensor, its telling you how big a load it can handle - nothing to do with the consumption of the sensor itself. Its like payload, not unladen weight...
Have a look here:
So the device works from 6 to 36V (Chinese 36 probably),
and it will put out the supplied voltage on the output.
It is claimed to be capable of drawing 150 mA, it does not use it on lighter loads.
ok so i picked up a multimeter and tested the sensor. at idle it was pulling about 4.6ma and with the magnet near the sensor it pulled a maximum of 7.8ma. now that i know how much the sensor actually pulls my final question is what is the maximum current i can pull thru the 2560, the plan is to have two of these hall effects and the temp probe which would put me around 20ma total, is this safe to run directly off the board?
Here is what the data sheet says about current limits. Note that the recommended maximum from any one pin is 20mA.
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