hi guys,
I am a very new newbie to the world of electronics and need some advices:
I would like to use RFID for this project:

Let's someone walks to my home and is equiped with my RFID, I would like to have a speaker at home announcing the person getting close.

So first I am wondering if the RFID on the person can be without a battery, or with minimal battery
And in my house whay do I need ?
Any specifications ? brand ?

thank you in advance

Originally Posted by Smithy2k8

hi guys,
I am a very new newbie to the world of electronics and need some advices:
I would like to use RFID for this project:

Let's someone walks to my home and is equiped with my RFID, I would like to have a speaker at home announcing the person getting close.

So first I am wondering if the RFID on the person can be without a battery, or with minimal battery
And in my house whay do I need ?
Any specifications ? brand ?

thank you in advance

RFID tags are short range devices, so you probably need something active. There are dozens of active devices around but none that I know of that continuously transmit a code in the way you describe. That would be a bad idea anyway - who needs more RFI?? Plus the battery would go dead in short order (RF is by its nature a power hungry activity).

You would have to construct something that sent a query out to a listening receiver, if the receiver hears it, it would respond with a code that says something like 'Hi - Fred here!'. This is in the realm of radio network infrastructure engineering... perhaps you need a Zigbee and a microcontroller for this, or just an embedded Zigbee module or similar. Watch out though, the more friends you have, the harder the problem gets...

It's a non trivial project.

Anyway, I was curious - why do you need to keep 'tabs' on your friends? Are they out to get you!??! Perhaps you should just give the mower back....!

-CF

not with RFID, it is passive short range device, but CF already elaborated on that ...

you can do it with BT. Most people nowadays (for unknown reasons to me) have their BT module on their cell phones turned on. For those in "discoverable" mode, you can detect them if they want or do not want you to. For those in "non discoverable" mode, you will have to pair those devices to your system before you can "detect" their presence.

As each BT device has it's unique MAC address, it is not a problem to distinguish between your friends.

With some older BT phones, you can detect their presence (and read MAC address) even if they are not in discoverable mode (it is enough that they are on) - I have not tried with "new" phones but it might still work. You will need a specialised application for that...

Hi guys, Carlos, Arhu
sorry i lost the forum address for a while, took me some time to find it !
thanks a lot for your answer and guiding me in my first steps

Ok it's not keep tabs on my friends
it's more like a fidelity program.
For example I would like to give customers a special badge when they are getting close to the my business I would like to be able to know that they are getting close to provide them with a good sales rep
(for example)

So I need the badge to be picked up from about between 100m and 200m
Use very minimal power
On the other side it does not matter.
When it gets back the signal from the badge I can be averted throug the speaker.

I have no idea how to start, i would like to use possibilly out of the shelf products

thank you for your kind help,
regards

Originally Posted by Smithy2k8

Hi guys, Carlos, Arhu
sorry i lost the forum address for a while, took me some time to find it !
thanks a lot for your answer and guiding me in my first steps

Ok it's not keep tabs on my friends
it's more like a fidelity program.
For example I would like to give customers a special badge when they are getting close to the my business I would like to be able to know that they are getting close to provide them with a good sales rep
(for example)

So I need the badge to be picked up from about between 100m and 200m
Use very minimal power
On the other side it does not matter.
When it gets back the signal from the badge I can be averted throug the speaker.

I have no idea how to start, i would like to use possibilly out of the shelf products

thank you for your kind help,
regards

OK - the friends thing was just a joke!

Right then... well, the problem you have is on several levels. When designing something like this you have to consider several factors: size, cost, etc. but above all else, feasibility and scope. Regarding feasibility, I know of many rf tranceivers that you can get hold of. In fact I am using some in a project I am working on right at this very moment.But none of these are small enough to fit in a badge, and I don't know of any that are. And of course they won't work on their own, they need support kit like processors and voltage regulators.

On top of that, they all use a considerable amount of power - about 40mA. So even a PP3 (9v) battery would only last a few hours, at best. It's starting to look a bit awkward, overall. This is why rfid is so popular - they are small (or at least, thin) and don't require any power at all. But of course the range is only a couple of metres.

Regarding scope, the project I'm working on is for a large remote control tank. I have just completed the motor driver electronics and associated code, this took a considerable amount of know how and experience and took me about a week to do. The scope of this, I feel, is similar to what you would be required to do to realise your own project. If you are at absolute ground zero with such know-how, I think it would be a very rewarding experience to obtain this knowledge (and I urge you to do it!) - but I do think it would take you a lot longer than a week. Maybe a month, maybe a year!

Anyway, I'm rambling now. I don't want to put you off this, quite the opposite, I hope you pursue it with vigour. I suggest that you start looking for RF devices on the net (e.g., in the UK you could look at rfsolutions.co.uk). Then you need to get a pic programmer like the PicKit2 and some pic processors (microchip.com), start messing around with that and get into some LED falshing action. You can get a free C (or BASIC) compiler from sourceboost.com.

I doubt this has helped you much!

-CF

Originally Posted by arhi

not with RFID, it is passive short range device, but CF already elaborated on that ...

you can do it with BT. Most people nowadays (for unknown reasons to me) have their BT module on their cell phones turned on. For those in "discoverable" mode, you can detect them if they want or do not want you to. For those in "non discoverable" mode, you will have to pair those devices to your system before you can "detect" their presence.

As each BT device has it's unique MAC address, it is not a problem to distinguish between your friends.

With some older BT phones, you can detect their presence (and read MAC address) even if they are not in discoverable mode (it is enough that they are on) - I have not tried with "new" phones but it might still work. You will need a specialised application for that...

This is actually a very good idea, having re-read this thread in more detail. The mobile phone approach is a good one, but it does depend on the phone's bt being set to discoverable etc. Still it's a better solution and there are bluretooth modules that will allow this kind of data to be collected and processed. Maybe it's worth chasing that for a while!

For long distance, your badge will have to be an active transmitter. There's an example transmitter schematic in this app note:
http://www.rfm.com/products/apnotes/...ransmitter.pdf

You'll also need something like to feed a data stream into the transmitter, could be some logic chips, or more simply a microcontroller. You could program it to send a short unique customer code every, say, 20 seconds. Current consumption could therefore be tiny, and you could get away with using calculator cells, which may last for up to a year.

It will be very difficult getting the range you're after, especially with the badge being attached to a person (who will likely absorb the rf energy).

Hello
I am going to read all your posts and digest the information.
When I said badge i was not being very precise.
All i meant is something mobile (like a garage door opener)
But the point is that I would like it to be mobile and last for decent time without having to charge batteries or charing it (the cell phone way could be an alternative as well because you have to charge it whehter you want or not but this is another way).

It is important that the range is about 100m however.
I can see that there are many ways to approach the problem but from your point of view i was wondering what is the most optimized way considering my needs ?

Thank your for your help