Linear Hall Effect IC Comparison - Page 1
Forum section: electronics / beginners

author: john21443
author_rank: Contributor
timestamp: December 15, 2021, 04:36:59 pm
content: Hello,I am selecting a hall effect sensor to determine position of a foot pedal. Based on the current mechanics I have about 1" of linear motion and can control the size/placement of the magnet I am using. I am comparing 2 Texas Instrument ICs and confused by what I am seeing.Bipolar sensorhttps://www.ti.com/product/DRV5055-Q1#featuresthat has this sensitivity at a particular range: A4: 12.5 mV/mT, ±169-mT RangeUnipolar sensorhttps://www.ti.com/product/DRV5056-Q1#featuresthat has this sensitivity at a particular range: A4: 25 mV/mT, 158-mT RangeI would expect since the unipolar offering is operating across less range (158-mT vs. -169 to +169 mT) that it would be more sensitive. However, the opposite appears to be the case by a large margin.In my application I do not need bipolar capability but that looks like the way to go as my goal is maximum sensitivity.What am I missing?Thanks,John

author: KT88
author_rank: Frequent Contributor
timestamp: December 15, 2021, 05:16:44 pm
content: There are a lot of possibilities for such an application. Your approach seems to optimize for lowest cost by the choice of sensor. There are more sophisticated sensors that are more robust, less susceptible to dimensional tolerances, thermal drift, choice of magnet (ferrite vs. rare earth) and much more.You could trade engineerig effort vs. bom cost but ultimately the required position sensing accuracy is the defining design target - how does that look like?CheersAndreas

author: john21443
author_rank: Contributor
timestamp: December 15, 2021, 08:02:07 pm
content: Thanks for the information.In my application I don't currently need the additional sophistication. However, it is good to know there are solutions support it. I may look into them to get a more complete picture of what is available if my requirements change.For a first pass I would like to pick one of the two sensors I mentioned but still not sure why/how the one with more than twice the operating range has twice the sensitivity. It feels like it should be the opposite so there may be some trade-off I am missing.

author: Benta
author_rank: Super Contributor
timestamp: December 15, 2021, 08:22:56 pm
content: Quote from: john21443 on December 15, 2021, 04:36:59 pm25 mV/mT is to me more sensitive than 12.5 mV/mT (you know, larger output swing per mT). But perhaps my basic maths are failing me (I don't think so, though).

author: john21443
author_rank: Contributor
timestamp: December 15, 2021, 08:41:54 pm
content: You are probably right that I have it backwards. I had seen this in the datasheet and more than likely misinterpreted it:QuoteWhen I saw their product offerings I just assumed that the ones that handled larger amount of magnetic flux had greater sensitivity:QuoteI will think through this a bit more and may actually want the 20-mT range part!

author: john21443
author_rank: Contributor
timestamp: December 15, 2021, 10:40:17 pm
content: I think I have been confusing sensitivity with accuracy.The specs I pasted were for sensitivity. In my application I should be able to not be concerned about the sensitivity. I will look deeper into things to get a better understating of how relatively accurate these components are.Thanks again,John

author: Doctorandus_P
author_rank: Super Contributor
timestamp: December 16, 2021, 04:59:48 pm
content: What sort of resolution do you need?It's probably easier to use a HALL sensor that is made for detecting rotary motion, and then measure the rotation around the hinge point. These sensors can have upto 12 bits of resolution (4096 positions), which is about 11 ticks per degree. So if your pedal rotates 20 degrees around it's hinge point you already have over 200 detectable positions.You can also amplify the rotation with some gears, levers or a piece of string around a rod.

author: john21443
author_rank: Contributor
timestamp: December 16, 2021, 08:13:45 pm
content: Quote from: Doctorandus_P on December 16, 2021, 04:59:48 pmI will take a look at that approach.Thanks!

author: KT88
author_rank: Frequent Contributor
timestamp: December 17, 2021, 01:59:02 pm
content: AMR sensors could be advantageous for such a measurement as they are sensitive to the direction of the field with very low suscetability to changes of the field strenght.They eere available as two output devices with amplified sine- and cosine output. No further amps are required to hook the sensor top a uC...One example is the ADA4571 from Analog Devices - it is also quite cheaphttps://www.analog.com/en/products/ada4571.html.CheersAndreas

author: john21443
author_rank: Contributor
timestamp: December 17, 2021, 03:14:36 pm
content: That really helps me in figuring this out. It was getting a bit daunting researching as there appear to be a few different approaches for determining angle with hall effect and many interfaces.Thanks,John

author: KT88
author_rank: Frequent Contributor
timestamp: December 17, 2021, 03:22:41 pm
content: Position sensing with Hall sensors can get pretty challenging. Melexis has a family of Hall based sensors (Triaxis) but they are highly integrated and require programming with dedicated programmers and a quite challenging learning curve. But this techinque gives an idea what it takes to get to a viable approach for position sensing with Hall...

author: john21443
author_rank: Contributor
timestamp: December 24, 2021, 05:15:26 pm
content: As a follow-up I have implemented a solution for my pedal position sensing. Using the considerations and insight you all provided in this thread I settled on the AMS AS5600 to sense the rotation of a magnet at a pivot point of the pedal:https://ams.com/documents/20143/36005/AS5600_DS000365_5-00.pdfThis chip operates with 12-bit output. It puts out angle as an analog voltage, PWM signal or over I2C.It can be programmed via I2C or 3 wire signalling. No specialized programmer is required. I was able to prototype using an available breadboard:https://www.mouser.com/datasheet/2/588/AS5600_UG000254_2-00-1877354.pdfOne cool capability of the chip is that if start/stop angles are configured than 12-bit resolution is available over that subset of 360 degrees. This gives me 4096 positions over around 35 degrees. It is way overkill for my application but nice nonetheless.Thanks again,John