Hall Sensor isnt square wave

Hi all,

I am working on a kinetic sculpture involving an odrive and hoverboard motors scavenged from a Segway Ninebot S Pro. The specific motors are https://more4motion.com/products/motor-assembly-for-segway-minipro

While configuring odrive to work with the motors I ran into issues with the hall sensors. I was getting an Error 16 for hall sensors configuration and the shadow_count never changes beyond a constant 0.

I pulled out my oscillioscope (Siglent SDS1104X-E) and did some readings on the hall sensors.

Im not getting anywhere close to a square wave or 5v on this sensor. Judging by the NineBot S Pro board, it is indeed a 5v hall sensor. Pinouts labeled as HA, HB, HC, 5V, GND.

First I connected 5V+ and - to the 5V and GND of the hall sensor, then I connected my scope probe to one of the hall sensor leads, and the ground clip to the GND (-5V).

Does this make sense to anyone? This is my first time working with hall sensors. If anyone has any ideas or suggestions I’d be eternally grateful.

Attached are two screenshots from my oscilloscope readout:

Some Hall sensors are open-collector i.e. the signals need to be pulled up to 3.3v or 5v. Check that it isn’t one of those. It should be safe to try with a 10k resistor to 3.3v.

The encoder pins have 3.3k pullups on them already so shouldn’t be a problem, as long as it’s plugged into the ODrive :thinking:

Ahah. Thats wild.

Well apparently even via oscilloscope I had to have capacitors across the gnd and signal pins otherwise it was not square wave.

I ended up making a similar board to one that has been floating around here that had caps direclty connected near the board and it seems to have solved the issue. Previously I had 22nf capacitors but they were further away from the odrive board.

I dont entirely understand exactly what causes the signal interference from the other hall sensors. Is it EMF basically?