Hacker News Reader

Comment by retroafroman | Hacker News Reader

This sounds like it could be better to use RFID. Depending on the application of course. Could you go into more detail?

The idea is the basic indoor mall/store navigation thing: Each BT transmitter will send out a unique code tied to its location. An app on the phone detects the nearest n of these and determines location by triangulation.

If the sensors are cheap, they can placed dense enough to provide pretty good localization. The mall can pay for them. Say, if the transmitter is ~$5, we can place 200 of these in a mall for $1K, which isn't that much, I think. The transmitters should be low-power to minimize maintenance, e.g. go for a month or more. They should also be small to be unnoticeable.

What do you think?

Hmm. I figured you were depending on people's phones to do the reading. I assume you're doing this in order to help the customer navigate the store?

If you could have the customer pick up a handset RFID reader (with your app on it I suppose?) that they return when they leave, RFID could work. I suggested RFID because the tags don't need any battery or power supply. The readable range might be a little less than with Bluetooth transmitters, but I have seen read distances of 50 or so feet. And tags are cheap and readily available, too.

That is actually a good idea in settings where customers can/want to borrow a device from the store or mall, e.g. the RFID reader can be incorporated into the self checkout barcode readers that some supermarkets handout.

For a typical mall scenario, though, I think people will be reluctant to deal with the hassle of another device.

Right, another device is always a hassle. Anyway, food for thought.

A month of BT is going to require a pretty decent sized battery. (I seem to recall 4-5 mA idle, 40-50 mA while transmitting through one of those $40 BT modules.) Call it 10 mA average--you're looking at >7 Ah over a month. Assuming primary cells, that would be two C or D cells (actually, that's not too bad).

I think $5 is low. I'd guess more like $50 each for small quantity (<500) hand assembled in the US, using an off the shelf enclosure.

Does Apple even let you have access to the Bluetooth serial port profile?

It's a good idea, I was musing something similar recently actually.

So, you want to use a sensor type that a common smartphone can read, BT and Wifi seem to be the best choices.

Power wouldn't be a major issue, they would be plugged in to a wall outlet, or possibly even powered from a PoE line.

My mind is thinking about triangulation and the like. If the BT devices were networked, I believe you could have them transmitting an ID and a medium resolution time stamp. The phone would also have to be using network time and you could get a fairly accurate triangulation (again, I think, this part is far from my speciality).

There is a lot of merit to this idea. You could roll this into something to do with digital signage and advertising as well. As stores in a mall come and go, they have to update directories. You could build a system to let a mall auto-update it's layout maps as tenants change.

To support iPhones and iPods, you'll very likely need to join the MFi program.

Why not use GPS? The main problem to solve would be creating a database of the location of each store in the mall.

Did you find that there isn't enough GPS coverage in malls?

Reply on news.ycombinator.com