DIY Ebrake sensor - which reed switch?

L

liontail

100 mW
Joined
Oct 30, 2013
Messages
36
Hi,

I'm trying to figure out the best way to get ebrake functionality without having to use an actual ebrake lever. I'm tired of these cheap levers, and of course you can't use them for hydro!

I've searched the forums for the reed switches folks from here have used, but pretty much all of them seem to be normally open, and closed when a magnet is moved close to the switch. This isn't ideal for an ebrake lever, since the simplest strategy would be to mount the switch somewhere near the clamp and the magnet on the lever itself. When you brake, the magnet moves away from the switch and the contacts would ideally close...

Does anyone know of a good reed switch that's normally closed , waterproof, has good magnetic sensing characteristics for this purpose, and is reasonably price? I ordered a few of these from em3ev, but I'm still waiting for delivery. I'm also hoping for no external power needed - this uses the bafang's 3-pin plug, so I'm not sure.

I apologize if the answer to this question is somewhere on this forum already. I did try to search!
 
The trick is to search for reed switches that are 3 wire SPDT devices rather than 2-wire switches that are NC, and just ignore the NO contact.
You'll find many more options this way.

-Justin
 
You could just mount the magnet so it's close to the reed when the brakes are off and pulls away when the lever moves.
 
fechter said:
You could just mount the magnet so it's close to the reed when the brakes are off and pulls away when the lever moves.
Click to expand...

I see I got it backwards. The link above has some good suggestions.
 
Justin, you rock! In one line you got me on the right track.

For those who like me didn't know this, an SPDT reed switch stands for "Single Pull Double Throw", and it has 3 leads - common, normally closed (NC, and normally open (NO). It turns out there are a lot more of these sensors.

However, I'm not pulling up a lot that have the characteristics needed for a DIY ebrake sensor - namely small, and all wires entering/leading from the same side.

These might be promising:

http://www.ebay.com/itm/LOT-proximity-sensor-magnetic-reed-switch-developments-corp-2451-1301-102-SPDT-/321355736442?pt=LH_DefaultDomain_0&hash=item4ad24b657a

But they're big. I'll keep looking, and update if I find anything I'm excited about.

(To everyone else - mounting the magnet so that it's normally away from the sensor and then gets close when you depress the brakes often isn't easy, and is different for every brake lever. Kudos to agniusm, who figured out how to do it on shimano deore hydros in the link above.)
 
Here's my super cheap yet simple effort for cable brake switching using any levers:

http://endless-sphere.com/forums/viewtopic.php?f=3&t=65798&hilit=+magnetic

Magnets stick to the steel cable pretty well and the reed switch I found shrinkwraps to the noodle and doesn't interfere with removal.
 
liontail said:
Justin, you rock! In one line you got me on the right track.
For those who like me didn't know this, an SPDT reed switch stands for "Single Pull Double Throw", and it has 3 leads - common, normally closed (NC, and normally open (NO). It turns out there are a lot more of these sensors.
Click to expand...

Yeah I spent quite a bit of time in some futile hunting before realizing this, so might as well spare others the pain.

However, I'm not pulling up a lot that have the characteristics needed for a DIY ebrake sensor - namely small, and all wires entering/leading from the same side.
Click to expand...

If you do find those, what they are internally is just one of the small glass 3-wire sensors with leads inserted into a small plastic tube and then potted with resin, at like 4-5 times the price. We ordered samples of these in the MS08 size (~5mm diameter) which worked great for the application, :
http://www.misensor.info/reed-sensor/cylinder-reed-sensor

But then quite disappointingly when we went to do a formal order for 100pcs that were terminated with our ebrake connector standard and used a better cable etc. the final quote ended up at $1600, which seemed quite excessive so didn't pursue it further.

http://www.ebay.com/itm/LOT-proximity-sensor-magnetic-reed-switch-developments-corp-2451-1301-102-SPDT-/321355736442?pt=LH_DefaultDomain_0&hash=item4ad24b657a
But they're big. I'll keep looking, and update if I find anything I'm excited about.
Click to expand...

Yes the threaded ones seem perfect but all the ones we found in an appropriate thread size (M5 or M6) were only available as a regular Normally Open contact, and that's after contacting at least a dozen manufacturers. Certainly share anything good you find as there is no doubt a need for a good semi-universal solution here.

Another thing we've played with is a flexible pressure sensitive switch that you stick on the front of the lever itself. Then when your fingers on on the brake pulling it forwards it effectively closes contact to engage the ebrake, and you don't have to fiddle with moving parts.
 
I don't know why you would need SPDT when you could get nice NC reed switch. I found one that is 3.5mm in diameter and cost not that much compared the one in the link that you found. http://www.newark.com/comus-assemtech/s1372/switch-reed-proximity-3-5x18mm/dp/46W5571?ost=S1372

Justin mentioned flexible pressure sensitive switch but i would rather play with force sensitive resistors like these ones:
fsr_all_med.jpg

to get variable regen ;)
 
agniusm said:
I don't know why you would need SPDT when you could get nice NC reed switch. I found one that is 3.5mm in diameter and cost not that much compared the one in the link that you found. http://www.newark.com/comus-assemtech/s1372/switch-reed-proximity-3-5x18mm/dp/46W5571?ost=S1372
Click to expand...
That one's actually Normally Open as well. There aren't many Normally Closed around, and I don't know of any that are usefully small. Do post up any you may find as I'd be interested myself, either NC or SPDT (single pole double throw).

Michael
 
Right, skipped some info on the first post but why make it difficult if it works with NO contacts and implementation into brake lever is rather simple and elegant? If you still want to pursue the NC road, why not get glass reed switch, solder required cables and dip into desired round epoxy mold?
 
agniusm said:
Justin mentioned flexible pressure sensitive switch but i would rather play with force sensitive resistors like these ones:
<snip>
to get variable regen ;)
Click to expand...

Actually these are exactly the style we've been toying with. If you get one that has a low resistance (like 100 ohms) then it effectively closes the switch for a digital ebrake input, and would also provide avenue to have variable proportional regen with a small add-on circuitry that could look at the varying resistance and scale into a separate voltage signal for controllers that support it.

The slider style linear touch poteniometers could let you slide your finger left and right on the lever to change the regen intensity, while the pressure sensitive models generally need enough force that the mechanical brakes are engaged so you have something to press against.

And yes, your example reed switch highlights exactly the sourcing problem we've been talking about; all the reed sensors that are readily available in a convenient form factor for DIY ebrake cutoffs tend to be Normally Open devices, not Normally Closed as we'd want. Unfortunately Newark doesn't let you filter by contact form but after opening a dozen different ones that looked good they were also NO. The Hamlin model they list is available in NC, but that's an M8 thread size which is too large for a discrete install:
http://www.newark.com/hamlin/59065-010/magnetic-sensor/dp/05M4565
 
agniusm said:
I found one that is tiny and SPDT:
Click to expand...

Hmm, those are all great finds, nice work! Especially the threaded one with M6 threads, that makes it easy to design something with adjustable and re-adjustable positioning.
 
I've been playing around with ebrake sensors, and I've settled on my favorite:

http://em3ev.com/store/index.php?route=product/product&product_id=196

Super easy to use, NC, ready to go. Just 2 wires, too! You can also get them here:

http://www.elifebike.com/peng/iview.asp?KeyID=dtpic-2014-C5-0JU4.7TTSP
 
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