SMD Hall switch with ~3 KHz bandwidth? - Page 1
Forum section: electronics / projects

author: IDEngineer
author_rank: Super Contributor
timestamp: July 16, 2020, 04:37:48 pm
content: I'm trying to find a readily available, omnipolar, SMD Hall effect switch to sense motor rotation up to ~2500 RPM. We'll have a single magnet on the shaft coupler and the PCB will have the Hall switch mounted directly below the shaft so it can sense the magnet as it passes by once per revolution. Prefer push-pull output with operation on a 5V supply.It appears the SMD Hall switches that are deeply stocked at DigiKey, etc. are meant for human interface applications. They have max operating frequencies in the tens of Hertz. I did find a couple with higher "bandwidth" but they don't appear as deeply stocked so I worry about availability.Anyone spec'd a Hall switch like this before? Any pointers toward good (or away from bad) devices? Thanks!

author: georges80
author_rank: Frequent Contributor
timestamp: July 17, 2020, 09:12:34 pm
content: The 'low' speed hall sensors are low power, i.e. the hall sensor 'sleeps' for a period of time and then wakes up to sample. So, low bandwidth but the benefit is very low power consumption.The high frequency stuff doesn't 'sleep'.I've used the DRV5033 TI part. It's good to 10kHz+ and digikey has lots in stock (10's of thousands). This is just one example SOT23 part.cheers,george.

author: cdev
author_rank: Super Contributor
timestamp: July 18, 2020, 12:36:00 pm
content: cant you use optical sensors and/or a coil with magnet or capacitance or whatever to sense rotation by other means?

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2020, 03:22:45 pm
content: Quote from: georges80 on July 17, 2020, 09:12:34 pmGreat recommendation! It also comes in a TO92 package which will be handy for breadboarding. I wish it had a push-pull output but the spec sheet shows a clean square wave at 10KHz and we can read it with a Schmitt Trigger input so no problem.Awesome, thanks again for the tip!

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2020, 03:25:23 pm
content: Quote from: cdev on July 18, 2020, 12:36:00 pmWe're specifically using a Hall switch and magnet because this is a marine application (potentially wet and dirty). The PCB and its components will be potted for that reason, as well as to obtain SAE J1171 certification. We're concerned that optical sensors could become obscured, water has a high dielectric constant so it could affect capacitive techniques, etc. We're open to alternatives but at the moment a Hall switch looks pretty good.

author: georges80
author_rank: Frequent Contributor
timestamp: July 18, 2020, 04:51:43 pm
content: Additionally you mentioned the motor is running at around 2500rpm (that's revs per minute)...So, your pulse rate is 2500/60 per secondcheers,george.

author: IDEngineer
author_rank: Super Contributor
timestamp: July 18, 2020, 08:24:59 pm
content: {blush} Yeah, I kinda got wrapped up in the component search there. Thanks!That does open up some alternative possibilities for slower devices. But I'm liking the DRV5033. I've also found the Diodes AH3582, which is pin compatible with the TI part and, also like that part, comes in a throughhole version convenient for breadboarding. A bit cheaper too (because it's not TI) and stocked in five digit quantities. The only difference is the TI part is true open drain while the Diodes part has an internal pullup, but the latter is pretty weak and we can selectively populate the pullup resistor depending upon the part d'jour. Or, just have the external pullup be relatively weak too and always stuff it.