Hall effect speed sensor question
Hall effect speed sensor question
(OP)
I have a Cherry GS1005 Hall effect sensor that I'm trying to use as a cam position sensor. It should be triggering off a tab on the cam sprocket but I'm getting no signal on my scope. I have verified the 5V Vcc is there, and I have a 1K pull up resister between Vcc and the signal out (as per Cherry's installation document). However on the outside of the bag the sensor came in was a sticker stating that current should be limited via a resistor to 25mA. I'm using a 20ohm resistor but I'm not sure I did that calculation right (I'm going on an electronics class I took a long time ago) I also don't know enough to know if this sensor is working properly or if the tab I'm trying to use as a trigger is triggering. If I pull the sensor out should I be able to trigger it or at least get some sort of out put by moving a piece of ferrous metal in front of if? Can someone give me some advise on testing this sensor?





RE: Hall effect speed sensor question
Second, where did you put that 20 ohm resistor? Not loading the output - I hope.
Third, 1 kohm fom output to +5V sounds right.
Fourth, you didn't forget the 0 V connection? It happens sometimes.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Hall effect speed sensor question
RE: Hall effect speed sensor question
You might consider mocking up the circuit on a test bench and get it working there first.
RE: Hall effect speed sensor question
So that leaves just my suggestion to get it working on the bench first. Good luck.
RE: Hall effect speed sensor question
Note also that the operating temperature limit of 105C or 125C may not include your engine's normal oil temperature, assuming we are talking about an IC engine's cam.
Mike Halloran
Pembroke Pines, FL, USA
RE: Hall effect speed sensor question
It would also be useful if you used the right terminology. Where, for instance, is the INPUT of a Hall sensor? In my world, the input is a change in magnetic field and no resistor can be connected there.
When you say that "The 20 ohm is on the input as a limiting resister" and that you calculated it from some data, I wonder what data? You have mentioned 5 V and 25 mA. If those are the data you used, you should arrive at 200 ohms. But still don't see where or why you should apply that. A diagram showing your hook-up could perhaps shed some light.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Hall effect speed sensor question
I calculated the 20ohm value from the source voltage (5v) minus the the voltage drop across the sensor from memory of read a spec somewhere (4.5v), leaving a deference of .5v. divided by the max current (.025A) equals 20 (ohms). Is this not the way to size a current limiting resistor? Last night I was able to get a signal on the scope after placing a 51ohm resister at V+. the signal wasn't great and I was out of time, so it waits till Monday.
RE: Hall effect speed sensor question
No, your calculation is based on wrong assumptions.
You do not need any current limiting resistor in series with your Vcc. Just connect to whatever voltage within specs that you have. Anyting between 4.5 and 24 V is OK.
The maximum current says how much you can pull out of or, in this case, sink with the output terminal.
Therefore, if you have +5V, you should never have less than 5/0.025 = 200 ohms pull-up from output to +5V. That's all there is to it. You have 1 kohm, so you are fine.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Hall effect speed sensor question
You want to hook the device up as shown on p. 15 of the data sheet. VCC (+5V) needs to be positive with respect to Ground (0V). 1K from the output to VCC.
John D