Magnetic Proximity Sensor

[fastbike]

I have a project that I've just started designing.  It's to motorise an existing cord drawn curtain track (Silent Gliss® 6350), which has a single curatin which pulls from right (fully open) to left (fully closed).

The mechanical design is proceeding well and I'm now looking at the control side of things.
I'm envisaging a small ESP32 style controller with two sensors  to detect when the curtain is open or closed.
I'd rather avoid a mechanical microswitch setup as the carrier floats freely in the track and designing a reliable cam system to activate the microswitches would be a pain.
Instead I'm looking to attach a magnetic proximity sensor at each end of the travel and glue a magnet to the carrier to trigger the sensor.

The profile looks like this
with the recess at the left side used for the attaching clips and the roller pulleys/carrier running in the channel at the bottom (labelled 5.4mm wide) The two semi circular extrusion channels are for the cord to run through.
I want to place the sensor in the recess at the top for aesthetic reasons (cables are hidden between ceiling and track)


So the question becomes: How far will a magnetic sensor like a Celduc Magnetic Proximity Sensor be able to detect through the alloy channel - or do I just need to get one and experiment with a magnet ?

[moffy]

It looks like a magnetic reed relay, like those used for window open/closed detection. Normally a few mm but it depends on the strength of the magnet.

[Someone]

Normally a few mm but it depends on the strength of the magnet.

This is the problem, trying to squeeze a magnet into the existing mechanism and have it align with the sensitivity of the sensor (which is undefined for the OPs example).

[fastbike]

I've done a bit more searching and found a parametric search on teh Celduc site.

Their part PHA11200 has a data sheet showing the sensitivity by distance which looks useful. It is designed for PCB mounting but I can solder the lead directly and epoxy it into the track.

https://nz.rs-online.com/web/p/magnetic-proximity-switches/2180192

[moffy]

Here are some reed switches and magnets from the Jaycar site: https://www.jaycar.com.au/components-electromechanical/switches/reed-switches/c/2CI

[Renate]

I use Standex-Meder Electronics ORD 213/20-30 AT a bunch in Android devices.
To get to Qualcomm EDL mode you have to short two test points (a GPIO and 1.8V source) while you reset the device.
I put in a reed switch to make it unnecessary to open the case when you need to do this.
I select the least sensitive model even though it doesn't matter if the switch is accidentally activated when the device is not being reset.
These switches are tiny.

[neillnz]

Have you considered a Hall effect switch?

I have used this one below with a 6mm neodymium magnet and had it detecting reliably at 20mm in free air.

https://www.digikey.co.nz/en/products/detail/allegro-microsystems/A1122LUA-T/2499094

[SteveThackery]

Have you considered a Hall effect switch?

Exactly what I was thinking. You can get analogue Hall sensors or binary (on-off) ones. They will work off a tiny magnet.

[mtwieg]

I would definitely go for hall sensors instead of reed relays. Should be cheaper and more reliable.

What is your extrusion made of? If steel, you'll likely need to cut some openings around the sensors.

If the extrusion is nonconductive (i.e. plastic) then inductive proximity sensors are also an option. Better than hall effect in terms of reliability and robustness, but probably overkill for this application.

[Renate]

I would definitely go for hall sensors instead of reed relays. Should be cheaper and more reliable.

Probably more reliable. Allegro are twice the price of the reed switch I mentioned.

A reed switch needs a 2 conductor feed, the Allegro a 3 conductor.
A reed switch is sensitive to N/S the Allegro only S.
(In this application it hardly makes a difference.)