Radio communication thats cheap?

Is there something similar to RFID systems that can do cheap, short distance radio communication?

the setup has to be very cheap, like about $1 in parts that can be stuck onto items like a barcode tag, then when passed near a scanner if the stored code is a match it can transmit something back

Is there a simple radio technique for up to 10 feet or so where a $1 circuit could hear the radio and if it matched some internal # hardwired, it could transmit back some simple 8-bit response?

The bit width isnt as important as how to transmit (circuitry) and how a cheap circuit can hear and react. Its similar to an RFID application, cant interfere with cell phones or computers

The transmitter side can be more complicated but the receiver thing has to be disposable

thanks

Joerg,

I don't think he does -- all he wanted was to get an ID back from the chip, and passive RFID tags usually do this by 'shorting out' the incoming field for one bit (say 0) and not the other (this really is done by placing a partially shorting the antenna terminals...). The drop is field strength is detected by a circuit similar to a grid dip meter.

Hi Bradley,

From your description above (...it can transmit something back...) it seems there is no receiver but what you really want on the tag is a transceiver.

Have you looked at Bluetooth?

Also, there is the not so trivial issue of supplying power to the tag unit. While a little lithium cell might fit the cost bill, there can be problems related to disposing of the 'disposable'. Environmental regulations, safety etc.

Regards, Joerg

Some security tags some close to that price. A number of coils, tuned by lasering off bridges might work. You pretty much need the device to go through a sensing coil, such as an exi.

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HI Joerg,

What will work for the first part of this is if the remote part just receives, if it can receive? Ill worry about the transceiver later

Bluetooth seems to be similar? to the ethernet over wireless protocol?

Thats overkill in this application, if the data rate is 2K baud? Thats plenty fast. The power part is solved, not an issue, lithium cells should be safe for normal disposal in public landfills if I recall, but I wouldnt, better to recycle.

All I want is to transmit something in an on/off code like NRZ, modulate an rf signal so that its level is stronger/weaker, maybe 4 unique levels

The uhf remote control idea would fit the application, it should handle the data rate. Seems like a person could use a 555 timer chip to send the signal for radio?

Its the radio part that throws me, Ive got nothing to create this from scratch and if I ever knew how, have forgotten.

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exi.

Right, the security tag idea but I dont have lots of $ to pay royalty or licensing fees and big development kits probably cost $1000's and it seems so simple, take a 555 timer chip, modulate it with NRZ, it drives a tiny antenna. I dont know how to make a radio transmitter or measure the SWR, then I just need a simple circuit that will receive on the fixed frequency, like a SAW? and output the modulated rf, I can do the rest from there.

The radio part is a mystery, I want to make a tiny radio ( and I dont mean the $19.95 Ramsey kits ), just take the signal from the open collector output of the 555 into an antenna, 125Khz ?

Hi Bradley,

Pretty much any old receiver chip should do. I'd look for chips that are, for example, designed to receive signals for door entry. Cars contain those but you'd need to look for one that can work off a low voltage battery. They've got to be there because I have seen other products, for example a safe that could be opened with a remote. So its receiver must have been on a battery and pretty low in power consumption.

Similar but not the same. Lower bandwidth but still overkill for the bandwidth you need.

I'd still check into that before going into mass production. It is certainly an issue for the European market.

Check with the major semi manufacturers. There are many 'one chip radio' solutions out there. Even some FM radio solutions could probably be modified to work elsewhere, like in a lower frequency ISM band. A month ago I saw these pocket radios at Walmart. With earphones they sold them for the whopping price of one Dollar. I am a very cost conscious designer but that blew me away.

Regards, Joerg

From your description above (...it can transmit something

chip,

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Right, just need the most basic radio transmission. Did more study its NOT passive RFID Im looking for, but active with a battery.

Sending back, transceiver? not needed yet, receive only, 10 feet or so

Can you explain your situation a bit more? In your original post you mentioned you want a device to respond if there is 'a match'. This implies that it can listen (receive) and respond (transmit). Now you say you don't need to transmit.

Also you say you want it active with a battery. Why? Is there more circuitry that needs to be powered than simply the match-an-id part?

The usual transponder devices are doing exactly you descibed in your original post:

• Take power from the base station RF (no battery needed)

• Respond with a code. This code can be unique per device and even configurable for some transponders. Matching is done on base station.

• Least amount of components in device, so probably more disposable than anything else.

What is your problem with that?

Joop