Externally powering a Hall Sensor

[MisterE]

Hey Rob,
I'm trying to implement a hall effect sensor, and I've run into an unexpected phenomenon.
I ordered the TI sensors recommended on p.45 of the manual. They're the DRV5056A1QLPGM, ordered from Mouser. My understanding of the three connections of the sensor (oriented with the beveled surface facing me and wires pointing downward, L to R are:
1) Power (3.3-5V)
2) Ground
3) Sense
I wired the TS connection to the PED input of the eDRUMin it per the manual: Tip to sense (3), sleeve to ground (2). The sensor itself getting powered from a USB 5V power source.
I set it to Roland polarity, and the pedal type to Roland VH-12, just as the manual says.

Here's the strange thing. Without a magnet in proximity to the sensor, the eDRUMin control app shows the pedal low, almost closed. As I bring my magnet closer to the sensor, the pedal position goes up vs. down, as if the polarity of the magnet is reversed. Sensitivity and range are excellent; it's just reversing the direction of the pedal position. If I turn the magnet over, it does go in the other direction, but the sensitivity and range of motion are very, very low.

I tried this same sensor plugged in exactly the same way to my Pear Mimic Pro, and I get the very same phenomenon. With no pedal nearby, the position is very low, almost closed. The closer the magnet is to the sensor, the higher up the pedal position becomes in the PMP. don't believe I've wired anything incorrectly, and in fact I don't think that this phenomenon would be explained with incorrect wiring. Is it possible I received the wrong sensors?

Thanks, Rob!

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[Rob]

There is nothing wrong with the sensor. You should be powering it with only 3.3V not 5V. As mentioned in the manual, by using 5V you risk damaging your eDRUMin.

With the one orientation, the voltage is probably changing from something like 0V - 2.5V, which is within the proper range, so the eDRUMin is happy and measures a total range of 2.5V.

With the opposite orientation, the voltage is probably changing from something like 5V - 2.5V, but the eDRUMin can only read voltages below 3.3V, so the effective range is 3.3V - 2.5 = 0.8V. And on top of that, the eDRUMin needs to try to deal with an over voltage situation. It has protection diodes which may protect it, but I can't be sure if that won't cause permanent damage over the long run.

Again, by sending more than 3.3V to the eDRUMin pedal input, you risk damaging your unit, so I recommend using a 3.3V supply. If you are stubborn and want to keep using the 5V supply and are not concerned with the risk of damaging your eDRUMin, just stick with the orientation that gives the highest sensitivity and enable the 'invert' button.

[MisterE]

There is nothing wrong with the sensor. You should be powering it with only 3.3V not 5V. As mentioned in the manual, by using 5V you risk damaging your eDRUMin.

With the one orientation, the voltage is probably changing from something like 0V - 2.5V, which is within the proper range, so the eDRUMin is happy and measures a total range of 2.5V.

With the opposite orientation, the voltage is probably changing from something like 5V - 2.5V, but the eDRUMin can only read voltages below 3.3V, so the effective range is 3.3V - 2.5 = 0.8V. And on top of that, the eDRUMin needs to try to deal with an over voltage situation. It has protection diodes which may protect it, but I can't be sure if that won't cause permanent damage over the long run.

Again, by sending more than 3.3V to the eDRUMin pedal input, you risk damaging your unit, so I recommend using a 3.3V supply. If you are stubborn and want to keep using the 5V supply and are not concerned with the risk of damaging your eDRUMin, just stick with the orientation that gives the highest sensitivity and enable the 'invert' button.

Thanks so much for that answer. To verify, yes, the USB socket I have is 5V. I was anxious (and maybe even stupid) to test out the sensor with what I had availabe. I didn't realize overpowering it would result in that phenomenon, and I definitely don't want to damage the eDRUMin or PMP! Both are still working 100% fine with my Roland FD-9, so they're probably not harmed. In any case, I'll test it out with 3.3V and let you know. I really appreciate this, Rob!

[MisterE]

Thanks again, Rob,

Following your advice, I had an arduino power module in my parts bin that has both 5V and tried 3.3V settings and yesterday got to work at the breadboard. I set it up with 3.3V and tested it with volt meter to be verify I had 3.3V. All good. I saw no difference in behavior of the Hall sensor and the few magnets I tried between 5V and 3.3V. (I was either brave or stupid enough to quickly test both again with my eDRUMin 4. No harm done in fact, and it still works with my FD-9 and my Drone controllers as well as the Hall sensor.) I'll stick to 3.3V from here on though. Incidentally, is there anything wrong with using a 3V (nominally labeled) power supply, or is 3.3V more highly recommended? Scanning various electronics forums, I see varying opinions on whether there's actually a real difference in practice. The reason I'm asking is I will likely be making a Hall sensor for the Pearl Miimic which doesn't have 3.3V to tap into. I assume the only difference will with calibration and range with no detrimental effect on anything in terms of hardware.

In effect (no pun intended), my only error before my initial post was not selecting "invert". I think it was too late in the evening at that time, and I missed the obvious. I have never implemented that button before with other controllers and forgot that it might be necessary for a Hall sensor, which apparently it is. I was initially unaware of the fact that with proper magnet orientation (N/S) and position, as a magnet approaches a Hall sensor, voltage at the "sense" wire increases . It's the reverse of resistance-type foot controllers (Roland FD-9 for example).

WIth the magnet in the proper orientation and position, and the controller set to "invert", I was able to calibrate the eDRUMin easily and get good range and excellent sensitivity. However, as I noted in the original post, if I flip the magnet around, I the pedal travels in the expected direction without requiring "invert", but the range is only 25% or so that of the other polarity, and the behavior is wonky. I assume this is just because the polarity is wrong in that position, and these observations are normal behavior for that set of conditions.

FWIW all of this testing and experimentation has been done on a breadboard. Now that I have magnets, sensors, distances, orientations and eDRUMin Control software etc worked out, I'm ready to move to hi hat installation which should now be relatively easy. I received a 3D printer as a gift over the holidays, so it's time to move over to that learning curve.

In any case, have you been able to get your Hall sensor to work with a Roland, Pearl Mimic or other module? My instincts tell me that for any/all modules on the market (except the eDRUMin), a voltage increase means pedal up, and voltage decrease means pedal down, as they typically work with resistance. I assume this is why you implemented the "invert" button - specifically for Hall sensors. Is this correct?

Thanks, again, Rob!
MrE

[Rob]

I assume this is why you implemented the "invert" button - specifically for Hall sensors. Is this correct?

No. The invert control is there for inverting the voltage range, which could be useful for any number of reasons. With my Hall sensor setup, I do not use the invert control.

Are all your eDRUMin devices first generation? (ED10R1, ED4R1). If you have any of the second generation devices, then you can simply power that Hall sensor from the pedal input, which is highly desirable.

[MisterE]

I assume this is why you implemented the "invert" button - specifically for Hall sensors. Is this correct?

No. The invert control is there for inverting the voltage range, which could be useful for any number of reasons. With my Hall sensor setup, I do not use the invert control.

Are all your eDRUMin devices first generation? (ED10R1, ED4R1). If you have any of the second generation devices, then you can simply power that Hall sensor from the pedal input, which is highly desirable.

On your response 1:
Wow, that's interesting. As noted, I thought I had to use invert voltage fundamentally for a Hall sensor. I'll have to do some more testing with my configurations to see what's going on there.

On your response 2:
I am an early adopter and may have had a Gen 1 eDRRUMin , but when I get back to my studio/shop Monday, I'll investigate that as well. I have one of each (4 and 10) and bought/sold along one or two along the way, so I'm not sure what I now have. I agree, for eDRUMin/Hall applications, not having to introduce external power is a huge plus!

EDIT:
After using the eDRUMin's internal power from the PED jack (ring position) and selecting "Expression Pedal" I got it to work as expected. Thanks for the support, Rob.

Greatly appreciate your feedback and input!

[MisterE]

Hi,
I posted this as an edit to the above entry, but for those who might be monitoring this thread, I'm adding this entry so this entry shows up under your "active topics" for those following.

Update: After using the eDRUMin's internal power from the PED jack (ring position) and selecting "Expression Pedal", I got it to work as expected using Rob's recommended Hall Sensor, a DRV5056A1QLPGM.
See the TI Spec page here:
https://www.ti.com/product/DRV5056/part ... lsrc=aw.ds

According to that document, "Featuring a unipolar magnetic response, the analog output drives 0.6 V when no magnetic field is present, and increases when a south magnetic pole is applied."

Rob, I believe the following to be apply to the eDRUMin and use of the DRV5056A1QLPGM, but I welcome any corrections/feedback:
Per the TI spec page above, when no magnet is detected the starting voltage is 0.6V.
As with most Hall sensors, when a South pole approaches the DRV5056A1QLPGM, voltage goes UP to a max of VCC, or 3.3V when that voltage is applied. The range is therefore 0.6V to 3.3V which is quite broad as compared to other sensors which typically start at VCC/2 and go up to VCC when a South pole is applied.
As with other hall sensors, if a North pole approaches the DRV5056A1QLPGM, voltage does go down, but only from 0.6V to about 0.1 volt. That's a very limited range and is why I didn't find the Hall sensor useful with my PMP. No problem - I'll just use the eDRUMin between the hi hat and the PMP. It works so well!
The eDRUMin is particularly compatible with Hall sensors because its Expression Pedal setting works with pedals that start at a low voltage (no movement of pedal), and voltage increases as the pedal is pressed downward (magnet and sensor get closer.)
By contrast, most eDrum modules' hi hat controllers use resistance based controllers e.g. Roland FD-9 (as does the hi hat setting of the eDRUMin which is highly adaptable) and therefore expect the highest voltage when the pedal is up and decreasing voltages as the pedal is pressed downward.

In any case, all is well with the DRV5056A1QLPGM and the eDRUMin while using "Expression Pedal".

Thanks, Rob.

[Rob]

I don't have the invert enabled and still get about 2V of range. Did you notice this from the datasheet? I suspect mine is most similar to the image on the right.

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[Rob]

I had another look and it's definitely more like the setup on the right, with the magnet right over top of the sensor. I get a range of 1.2V with my foot off the pedal, and about 3.2V pressing firmly down, and if I lift the pedal up, the voltage goes all the way down to 0.6V. I don't have a magnet with labeled poles, so I can't be sure if the south pole or the north pole is down, but I suspect it's the prior.

Can you post a screenshot of your eDRUMin settings for your pedal input?

[Rob]

The eDRUMin is particularly compatible with Hall sensors because its Expression Pedal setting works with pedals that start at a low voltage (no movement of pedal), and voltage increases as the pedal is pressed downward (magnet and sensor get closer.)

This is correct, and should be the case the when the pedal type is set to Expression Pedal and invert is not enabled.

By contrast, most eDrum modules' hi hat controllers use resistance based controllers e.g. Roland FD-9 (as does the hi hat setting of the eDRUMin which is highly adaptable) and therefore expect the highest voltage when the pedal is up and decreasing voltages as the pedal is pressed downward.

Also correct.


And yes, your hall effect design probably isn't compatible with Roland modules. Unless Roland modules have some sort of 'invert' control, you would probably need to add an inverting unity gain opamp to your circuit.

https://www.dummies.com/article/technol ... er-179967/