TheBackShed.com

Forum Index : Microcontroller and PC projects : Hall Effect Sensor

Author

Message

palcal

Guru

Joined: 12/10/2011
Location: Australia
Posts: 2006

Posted: 09:44pm 13 Apr 2019

Copy link to clipboard

Print this post

I have a rain gauge in which I replaced the reed switch with a hall effect device.
The device switches on high to low on pin 15 of an E-28 (MM V5.04) set to CIN. The problem is it counts a random number of mm. every time anything inductive is switched on/off in the workshop. Thinking it was a dirty supply I tried running off battery power with the same result. Is it possible that the magnetic fields of my power supply, fluorescent light etc. are affecting the hall effect switch although it is over one metre away.
The rain gauge is in situ mounted on the roof of the workshop, at the moment the electronics (E-28, Wi-FI, and temp. humidity sensors) are still on the bench with a cable about 2 metres long going up to the rain gauge. Maybe this long cable is the problem?

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

goc30

Guru

Joined: 12/04/2017
Location: France
Posts: 435

Posted: 10:56pm 13 Apr 2019

Copy link to clipboard

Print this post

hi

I think it must be many parasites on the line. The counter must react too fast. Maybe you need to add an RC filter to damp the signal. Especially that the rain gauge reacts with a certain inertia. Other clean solution is to add an AOP in comparator mode and use the output of AOP to send in CINEdited by goc30 2019-04-15

PeterB
Guru

Joined: 05/02/2015
Location: Australia
Posts: 655

Posted: 12:49am 14 Apr 2019

Copy link to clipboard

Print this post

Good morning

A few questions if I may?
did the reed switch use 2 wires and go to the same CIN pin?
does the Hall switch use 3 wires?
does the Hall switch have a C across it?
can you hang a CRO / DSO across it to see what is going on?
does CIN need a pullup?
how's the weather?
my rain gauge failed because of a guild up of cobwebs.

Peter

for guild read build

PEdited by PeterB 2019-04-15

palcal

Guru

Joined: 12/10/2011
Location: Australia
Posts: 2006

Posted: 01:21am 14 Apr 2019

Copy link to clipboard

Print this post

I never used the rain gauge when it had the reed switch, I just figured I would change it to hall effect for reliability to use in this project. The hall effect module has 3 wires, it is 3144 hall effect sensor connected to an LM393 comparator and a pot for sensitivity. It does not have a C accross it. My CRO packed it in a few weeks back and they are so expensive. As for a pullup I don't know.
I think I may be better off getting rid of the module and using a bare hall effect sensor, I just had this on hand so I used it.

edit..tried a 10K pullup, no differenceEdited by palcal 2019-04-15

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

PeterB
Guru

Joined: 05/02/2015
Location: Australia
Posts: 655

Posted: 01:53am 14 Apr 2019

Copy link to clipboard

Print this post

The 3144 is open collector and so there must be a pullup. Also, a C from Vcc to Gnd is important.
There is also the idea of shielded cable.
Life without a CRO.......SHUDDER. (Grogster seems to survive without one)

Peter

palcal

Guru

Joined: 12/10/2011
Location: Australia
Posts: 2006

Posted: 01:56am 14 Apr 2019

Copy link to clipboard

Print this post

As my edit above, I tried a pullup, but I think the module probably has one
What size cap. 100n ? If it is needed there would be one on the module.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

PeterB
Guru

Joined: 05/02/2015
Location: Australia
Posts: 655

Posted: 02:09am 14 Apr 2019

Copy link to clipboard

Print this post

Perhaps you can get the Hall module on the bench and try different magnet orientations
I think the 3144 is sensitive on one side only and magnetic field determines up / down.
The module you are using seems to be designed for just this sort of thing so you must be close.

Peter

palcal

Guru

Joined: 12/10/2011
Location: Australia
Posts: 2006

Posted: 02:20am 14 Apr 2019

Copy link to clipboard

Print this post

Unfortunately the magnet is embedded in the tipping bucket.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

PeterB
Guru

Joined: 05/02/2015
Location: Australia
Posts: 655

Posted: 02:24am 14 Apr 2019

Copy link to clipboard

Print this post

I was thinking you could use a similar magnet on the bench just to see what orientation and gap does.

Peter

palcal

Guru

Joined: 12/10/2011
Location: Australia
Posts: 2006

Posted: 02:40am 14 Apr 2019

Copy link to clipboard

Print this post

I have another sensor the same, I will play around on the bench and see what happens.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

palcal

Guru

Joined: 12/10/2011
Location: Australia
Posts: 2006

Posted: 03:12am 14 Apr 2019

Copy link to clipboard

Print this post

Problem solved. I connected up the spare module on the bench with a short lead and it worked perfectly, so I then used a lead the same length as on the rain gauge and problems again.So a short shielded lead should stop any interference.
Thanks Peter.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

PeterB
Guru

Joined: 05/02/2015
Location: Australia
Posts: 655

Posted: 03:49am 14 Apr 2019

Copy link to clipboard

Print this post

goc30 nailed it but I am worried that such a short cable could cause that much strife.
It gave me something to think about while I did the washing. I probably put sox in with the whites but who cares?

Peter

palcal

Guru

Joined: 12/10/2011
Location: Australia
Posts: 2006

Posted: 03:58am 14 Apr 2019

Copy link to clipboard

Print this post

Yes, thanks Goc.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

PeterB
Guru

Joined: 05/02/2015
Location: Australia
Posts: 655

Posted: 02:50pm 15 Apr 2019

Copy link to clipboard

Print this post

Sorry Paul.
I should have thought of this before. An optoisolator e.g. 4N25, would help prevent spurious spikes and and would also give some protection to the E28 against zapping the cable with higher voltages not that we ever do.

Peter

palcal

Guru

Joined: 12/10/2011
Location: Australia
Posts: 2006

Posted: 03:04am 16 Apr 2019

Copy link to clipboard

Print this post

@ PeterB
I don't think it would help,the problem was caused by RFI on the lead to the Hall sensor. I ran the unit from battery power to eliminate mains interference and still had the problem.

"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"

Print this page

To reply to this topic, you need to log in.