Solution for (affordable) waterproof switch?


#1

I’m developing a sensor device that can be installed in swimming pools and will ordinarily be operated near the waterline (so either possible shallow immersion from time to time, or constant shallow immersion < 10 cm / 4").
I’m looking for an Off/On switch suitable for this application. Typically the switch will only be operated twice a year, for winterization and spring.
During installation, a user may accidentally drop the device in the deep end of the pool, so should also be able to withstand say <2.5m/9’ water depth for 30 minutes.
Most of the device will be potted in an epoxy.
AND, ideally would like a solution that will cost under $1-$2.

At one point I was using a reed switch, but at ~$4.50 found it expensive, plus the cost of pairing a magnet with it, and figuring a secure way to keep the magnet in place with the device remaining in the water seemed like a less than an ideal user solution.

I can only find a few waterproof switches listed on Digikey and many of them quickly get up into extremely high prices!

I feel like I’m missing something. Maybe I need more of a rubber seal instead of a sealed switch.

Any suggestions?


#2

Being that you are looking for the waterproof and the immersion depth and time I would probably go with the reed switch if that is a viable option. Not sure what you need for current specifications, however something like HE557-ND for about $0.50.

If you look at a toggle I think the best I can do is EG4914-ND or push button EG4890-ND however you are up to $4-$5 + going that route. If you need some more help with specs please let me know.

-Robert


#3

@bloukingfisher I was doing some more looking and I ran into one other option I though I would throw out. It is part 400AWMDP1R1M2QE-ND which is an On-On switch, however you should be able to wire it so it functions as an On-Off switch and it would be an IP67 Dust Tight, Waterproof option for less that $3. Not ideal, however might just work.

image


#4

Thanks @Robert_Fay
I should have added that the application is <5V and <100 mA.

For the reed I was looking at an NC circuit - so the majority of the year it would operate, and a magnet is only used to disable it to switch off. I looked at the same manufacturer but they don’t seem to have an SPST-NC option.

Once I start searching for IP68 (to account for an accidental drop in the deep end of the pool) the options and cost change dramatically. I may have to test or consider whether these IP67 options will be sufficient (or instruct the user to not drop it!).

I’m going to test this version with wiring for On-Off-Off: https://www.digikey.com/product-detail/en/e-switch/400UDP1L1BLKM2RE/EG5338-ND/5800208

Are there any off the shelf switch covers that could work with a wider range of switches? Meaning, I’m thinking that it has a hard plastic base that would secure in epoxy, but a rubber seal that would go over the switch? I’m concerned a simple rubber cover could break or loosen from the epoxy with repeated use.

Thanks again for the suggestions!


#5

Unfortunately I do not have anything that will keep the price down in the NC options for reed switches.

On the EG5338-ND I think if you have an accidental drop you will likely be Ok but testing is only done at 1 meter for 30 minutes on the IP67 rated parts.

The option if you wanted to look the cover way would be something like switch cover 335-1042-ND and switch 501PB-ND If you could pot the switch and the base of the cover the cover gives you an IP68 rating.

imageimage


#6

Thank you again!

I have actually been using that exact switch with this cover: https://www.digikey.com/product-detail/en/judco-manufacturing-inc/19-1088-00/513PB-ND/63952 but while it says environmentally sealed didn’t give me confidence for what kind of conditions other than dust proof.

But I’ve not looked at the switch cover before and see that actually has a rating. I’m going to try that! Alternatively, gave me an idea that with an O-ring I could use 513PB-ND.


#7

Sounds great! If there is anything more we can help with let us know.
-Robert


#8

Hi, bloukingfisher,

Hopefully, the cover Robert mentioned will work out. I did want to point out that there are some relatively low-cost reed switch options that you may have overlooked; specifically the SPDT versions.

https://www.digikey.com/short/qq3wtp

A few of these are pretty reasonably priced, and provide both a normally open and a normally closed option.

In 10 piece quantities, the 1835-1029-ND runs $1.70 each.

imageRI-90GP1520 Comus International | 1835-1029-ND DigiKey Electronics

I am also a little confused as to why you need normally closed contacts. If you are using this as a contact-less two position switch, the magnet has to be stable in two positions (near and far), right? If so, couldn’t you just reverse the logic (magnet near is ON, magnet far is OFF) and get the same results?

If you can do this, then the NO type reed switches can be found for under $0.50, such as the HE557-ND.

Perhaps I have misunderstood how you envisioned using the reed switch, but I thought I would throw this out there for you.


#9

Thanks @WOMROM

Maybe I don’t understand the wiring possibilities of the SPDT reed switches.

My thinking is that the device will be OFF when a magnet is in range (during winter when the device is either removed from the pool, or fewer worries about securing a magnet somehow with little hands, etc. around). In summer, the magnet can be packed away for the device to turn ON and operate in the pool.

So I was looking for normally closed contacts to conduct when a magnet was not present (I’m not envisioning a magnet like slide built into the device).

Thanks for throwing out the mention. I was trying to think if I could pair it with a transistor to work in reverse but not sure about the viability of that.

It is also low power device conserving a battery so wouldn’t want to waste battery during the OFF time.


#10

Hi @bloukingfisher,

First, regarding an SPDT reed switch, it has both an NO (normally open) contact AND an NC (normally closed) contact, so you can wire it either way.

image

Just wire to the NC lead and leave the NO lead unconnected and you have the equivalent of an SPST-NC switch.

Second, for using an SPST-NO type, I assumed you would not completely remove the magnet from the system in the ON mode, but rather you would re-position it (slide, flip, rotate, or whatever). Under such a scenario, it would not matter whether you used NC or NO. I see why you desire the the NC option if you plan to remove the magnet entirely. I would worry about the magnet getting lost during the extended time it is not being used, however. Would it be possible to tether the magnet to the system? Then you could use an NO type switch and not have to worry about losing the magnet, as a bonus.

It is possible to use the NO version and reverse the logic by adding a few other parts, but I can’t think of a way to draw less than a few tens of micro-amps continuously in this scenario. If that is too much current, then using the NC switch seems like the only viable option.


#11

OK, that is helpful @WOMROM - I’ll have to check that out to wire it as NC. Looks like that could save a good cost on the BOM vs. the NC reeds I was testing before running around $4 a piece.

I don’t have a way to really secure the magnet from prying little kids hands when they’re swimming, hence the need to remove it completely when in use. In sleep mode my device is using around 1.6 uA and overall gives me a 10+ year battery life. From quick calculations seems like an incremental 50 uA would reduce battery life by 5-6 years which would not be acceptable. So I think other parts would need to add no more than 10 uA and when considering additional components, costs, mounting, battery life seems like the better option is to wire the 1835-1029-ND for NC.

For the very loss-of-magnet scenario and other reasons, a switch would be a better solution as long as I can implement it at a reasonable cost and not increase the rate of failure due to water ingress.


#12

@Robert_Fay Sorry, a moderator/community standards question. Two of my posts in this thread are hidden due to “advertisement and overly promotional” and several members flagged it? I certainly don’t want to post something that is not welcome so could someone help me understand what to avoid?

I certainly did not advertise or promote my own product (which nobody could tell what it even is). Otherwise, I provided links to Digikey listed products (I have no personal interest in any component manufacturer), mostly to the very same products @Robert_Fay and @WOMROM so helpfully pointed out.

Sorry for being off topic, but seemed like the best context to ask this question.


#13

@bloukingfisher I saw the flags and it has been fixed. This appears to be a setting error and not actually anything someone flagged. I am looking into the issue.

Thank You
-Robert


#14

Perhaps a bit late for the OP’s needs, but for anybody else, membrane-type switches such as these can be made environment resistant for a fairly low unit cost, where production volumes are sufficient to spread out the initial setup charges for the requisite overlays and whatnot.


#15

Thanks @rick_1976 - I still don’t have a confirmed solution so open to additional input.

I went with the switch below (a variation of the rocker posted by @Robert_Fay ). However, once the PCB is coated in epoxy the switch gets stuck in one position (one prototype I was able with force to dislodge it, the other prototype it broke).

Initially, I thought maybe epoxy seeped from the bottom of the switch into the mechanism, but when looking closing at the enclosure I think that is unlikely. My remaining hypothesis is that either a) the epoxy shrinks a little applying pressure to the side walls interfering with the action, or b) the exothermic reaction from the epoxy is hot enough to cause something inside to melt.

I’m waiting for additional switches to arrive for further testing. I did email E-switch for guidance but haven’t heard from them.

image


#16

Hello @bloukingfisher,

I can also speak with my product manager to see if he has any ideas, however the two questions you have are probably more focused towards the epoxy manufacturer. They would likely know the reaction temp or expansion pressure that could be created. It may be helpful if that information is available prior to specking with ESwitch.

-Robert


#17

Thank you @Robert_Fay and happy holidays!

The urethane epoxy shrinkage is 0.01 in / in. The manufacturer doesn’t provide much detail (as each application, size, the environment is unique), but the post cure temperature (which I don’t do) is 150 F. I’ve not actually measured it, but by handling product being cured I would estimate in the range of 100F - 140F. So theoretically it should be well within the switch’s operating temperature range.

I’m still waiting for additional switches to arrive for testing (seems like USPS delivery is delayed). I’m planning 2 tests: a) test the switch in a vice to see if compressive pressure emulates the same behavior, and b) is raise the switch from the PCB to minimize the epoxy to as little as possible to the bottom of the switch to seal the contacts.


#18

Happy Holidays @bloukingfisher,

Yes that seems like it should be ok temperature wise.I would think that you should have plenty of room for expansion that you would have limited pressure being put on the switch itself. Please let me know the results of your testing and I can bring this up to my product manager to review.

Thank you
-Robert


#19

Hello @bloukingfisher,

I did speak with my product manager today from E-Switch and he stated the following.

The switch needs to be mounted in a box or panel that can be sealed. Usually, when a switch manufacturer states “Sealed” or “IP67” they are in reference to the front side of the panel, the rear is not. There are some that are rear sealed, however, they will be expensive. The epoxy the customer is using, is most likely entering the switch causing the contacts to seize. I would recommend a sealed box with a panel mount switch. Perhaps a boot as well.
If they decide to go with a toggle, they will need a boot that can handle chemicals such as chlorine. With a Push button, they can get the sealing they want, however, there would be no way to secure it from accidental actuation. Unless they look at switch guards. Either way the price will go up.

-Robert


#20

Thank you, with further testing I confirmed the problem was that epoxy was seeping into the mechanism from the bottom of the switch. Sealing the bottom with silicone before epoxy application seems to solve it.

I’m doing further testing and trying to evaluate the practicality of scaling this solution for manufacturing.