Idea for a AA battery sized BLE device locator

[Sonny_Jim]

So my brother had this idea literally decades ago, it's quite simple.  AA battery with a locator device, so sling it in your TV remote, when you lose it, press a button and it beeps so you can find it.

So flash foward to now and I see that there are lots of BLE based tracker products, this one in particular seems to be basically exactly what my brother had thought of;
https://www.indiegogo.com/projects/easyfinder-find-it-now#/story

Looking at that, it ticks all the boxes for a failed crowdfunded idea.  No demonstration of working prototype, missed deadlines, fakey McFake looking app etc etc.

So I thought I'd might have a go   A quick shufty around reveals this chipset which looks like a goer:
https://www.nordicsemi.com/eng/Products/Bluetooth-Smart-Bluetooth-low-energy/nRF51822-Bluetooth-Smart-Beacon-Kit

It's certainly small enough to fit into a battery sleeve and power requirements look ok.

What are your thoughts on this?  Good idea?  Possible?  I might lay out the £30 and pickup a dev kit and have a prod.

[Ian.M]

Something like half the remotes out there use AAA batteries.  If you are only supporting the AA form factor, you still have to power the device its in + the beacon.  What are you going to use to do that?  I'd probably go for a N cell, but that's expensive, with nothing like the capacity of an Alkaline AA, so  is going to significantly shorten the device's battery life.  All in all, its not surprising the campaign failed - its too niche and not high enough perceived value.   A meter of wide red ribbon + some double-sided sticky tape makes a far more effective remote locator!

OTOH if you make a slimline 1/2 credit card sized locator, that can be slipped in a wallet, attached to a keyring, or stuck to a remote, glasses case or whatever, its got a far wider market, and without the severe form factor constraints, is likely to be far easier to design and build at the desired price-point.

[Sonny_Jim]

Something like half the remotes out there use AAA batteries.

My thinking was to see if I could squeeze it into AA form factor, then try for AAA.  Thinking about it, would make more sense to try and go for AAA first.  It's a toss up between easy development at the start and harder later, or the other way around.  Considering it was my first try at something like this I went for the easy option

you still have to power the device its in + the beacon.  What are you going to use to do that?

This is kinda were it fell apart in my mind for me.  As you point out, it's going to be *expensive* to get a battery smaller than a AAA which is easily available.  What does work in my favour is that remote controls use teeny tiny amounts of power but looking at the datasheet it appears it really needs 1.8V, which is great if you are using coin cells, not so great when using a AAA/AA

A meter of wide red ribbon + some double-sided sticky tape makes a far more effective remote locator!

Would you really want a metres worth of stuff trailing from your remote, just so you can find it?

OTOH if you make a slimline 1/2 credit card sized locator, that can be slipped in a wallet, attached to a keyring, or stuck to a remote, glasses case or whatever

I've seen the stick-on locators and thought the form factor would give it a bit more USP to try and make it stand apart from the 100s of products like that already available.

Still might just buy one of the dev kits anyway, only £30 and should keep me amused for a bit.

[Ian.M]

AA/AAA powered remotes typically use a *LOT* of power, with peak currents of up to 100mA, but with a very low duty cycle, so the average power in normal use is minuscule.  However the high peak current requirement would be impossible to meet with many smaller cells.

I've BTDT with the red ribbon.  There are few more effective ways of stopping elderly relatives from loosing remotes.  Unfortunately it isn't practical for keys, wallets, bus passes etc.

[miguelvp]

Give it a go by all means, but some caveats:

Bluetooth antennas are not omnidirectional so depending on how they are oriented the range will suffer.
Class 2 BLE range is only 10 meters (33 feet) line of sight. (You'll need a class 1 device with its associated power consumption).
Battery cover might interfere with the antenna.
How important is bidirectional communication for this kind of application?

I haven't read the full bluetooth 4.0 spec so the range might be better than what I recall from the standard bluetooth ranges. But I would dig into the specs if I was you.

I think an RF receiver will be better suited and it is widely used for that.
Also there used to be sound receivers that you just have to whistle to find them.

Interference from other bluetooth devices might not be an issue for BLE since it does channel hopping and uses spread spectrum tech, but then again, research it to see what are the limitations on that end.

[Kilrah]

Wouldn't the beacon empty the battery in a week or 2?

[Sonny_Jim]

Wouldn't the beacon empty the battery in a week or 2?

Yes it seems that the chipset I linked to is a little OTT considering all the bells and whistles it can do, where really I just need it to beep.

I think an RF receiver will be better suited and it is widely used for that.

This was the original idea, but after seeing all these BT trackers pop up I thought it would be a good idea to use that tech.  Also it seems almost the law with crowdfunded projects to be able to use your phone with it, whether it makes sense to do so or not

Although I have a bit of background when it comes to electronics (I'm a pinball engineer) I am completely clueless when it comes to RF stuff.  Any pointers toward relevant low power RF things I can look at would be good.

[stmdude]

I've worked _a lot_ (and still do) with the nRF51822 chips.. They're awesome little devices, and not too bad on the wallet either.

What you want to do is actually part of a standard BLE "profile", called "alert".
The SDK for the nRF actually contains a working implementation of what you want to do, straight out of the box. (Well, it blinks a LED instead of beep, but close enough).

Prototyping is dead simple, using the QFN form-factor. The example circuits in the data-sheets work out of the box.

If you're careful with the software, you can get a BLE beacon/alert down to about 11uA average consumption (peaks of about 10mA when broadcasting), so a AAA battery will last a senior citizen the rest of their natural life.
A traditional CR2032 should last you about 2 years.

However, as miguelvp pointed out. RF tuning and getting maximum range out of these things is a task best left to proper RF people. You get pretty far by using the PCB antenna from the data-sheet, but its not something I'd run through a certification process without having it looked at/analyzed by and RF guy.

Also, you're dealing with RF and BlueTooth, so if you want to sell a product, you need to pay up about $5K (if I recall correctly) to register with the BT SIG, and you'll need to get FCC certification for the US market.

Then again, you'll need to do that for all RF products, not only Nordics stuff.

[station240]

Most TV remotes I've encountered use two AAA (or AA), side by side.
Should be doable to make a module that occupies the same space, but uses a 3.7V thin lipo cell, voltage regulation and the BLE device.

You could also have the BLE device report when the battery gets low and needs a recharge.

[miguelvp]

I think Wi-Fi Direct (aka Wi-Fi P2P) would be a better contender, there are some low power modules out there.

I don't know how good can Bluetooth or for that matter WiFi transmit when buried under your couch cushions.

[Sonny_Jim]

Most TV remotes I've encountered use two AAA (or AA), side by side.

In my experience, they can be either side by side or one on top of the other.  When they are side-by-side I would be nervous about the form factor fitting properly, as most manufacturers will have very slightly different battery compartments.  I suppose for prototyping I can just focus on the side-by-side option, as it would be the easiest to do.

If you're careful with the software, you can get a BLE beacon/alert down to about 11uA average consumption (peaks of about 10mA when broadcasting), so a AAA battery will last a senior citizen the rest of their natural life.

That's good!  And kinda what I thought it would be.

I don't know how good can Bluetooth or for that matter WiFi transmit when buried under your couch cushions.

Again, not an RF guy, but surely these devices should be able to work through that?  It's not like my cushions are made out of aluminium foil.  Might be an issue if it falls under the coach and the signal gets blocked by the faraday cage that are the seat springs.

You get pretty far by using the PCB antenna from the data-sheet, but its not something I'd run through a certification process without having it looked at/analyzed by and RF guy.

That's not so good :\  I hadn't thought about certification.  I was kinda hoping by using an off-the-shelf chipset I could dodge a lot of that.  Also I'm wondering how I'm going to design a PCB antenna that works in the form factor.  Again the side-by-side option would probably be a lot easier here.

Thanks for the pointers guys, even if I don't get to a prototype stage it's an interesting discussion and has given me a lot to think about!

[miguelvp]

Shouldn't be hard to find pre-certified modules.

Most manufacturers either offer them 1st party, or there are 3rd party manufacturers that do it, case in point nordic semi:

https://www.nordicsemi.com/Products/3rd-Party-Bluetooth-Smart-Modules

So I wouldn't let that slow you down.

[mark03]

The indiegogo project you saw may have failed, but it's not like these devices aren't already out there and commercially successful.  See e.g. www.xyfindit.com.  Why reinvent the wheel?

[Sonny_Jim]

As I said in a previous post, because (to me at least) the AA/AAA form factor would make it stand out a bit.  In fact it was seeing devices like that that made me think of paying this concept another visit, as it showed to me that there was a market and that the technology was cheaply available.

So, does everyone agree that BLE should be the way to go or should I be looking at other RF stuff, like a 433MHz device?

[miguelvp]

Not sure if it's still available but lower frequencies (43-50MHz) like old analog wireless phones back in the 90s used might give you more range through walls.

No security or minimum for eavesdropping and baby monitors shared the higher range of the spectrum. No spread spectrum tech either but they had no trouble going though brick walls.