nRF2401A used in an Anti-Lose Device?

Wireless & IoT
1

Hello all,

I’m working on a small project to prevent the loss of a very SMALL item. I want it remind the user via sound that he/she is leaving it behind accidentally when walking away at a 5 foot range. I was wondering if the nRF2401A would be appropriate for this application. Will I be able to set the distance/range to my own preference? or is there something on Sparkfun that would be more appropriate?

http://www.sparkfun.com/commerce/produc … cts_id=152

(nRF2401A Transceiver nRF2401A with Chip Antenna)

2

It doesn’t have any RSSI functions. However, you could butcher the antenna or casing to limit the transmission distance to suit your needs as a trace antenna going to another trace only has a 7-8 meter range anyway, and it would be easily reduced with a bit of foil etc…

Alternately the Microchip MRF24J40 has RSSI features and may be of use.

3

I’m thinking that one of the simpler OOK (ASK) transmitter/receiver pairs would work.

Keep the antennas short and the transmitter voltage lower to limit range.

The transmitter only needs a simple circuit to ‘chirp’ every second or so.

The receiver needs a circuit (processor) to recognize the transmitted ‘chirp’ and reset a timer.

If the timer expires due to not receiving a ‘chirp’ then sound the alarm.

4

Yeah, I was thinking it could be overkill but I wasnt too sure if the range of the antenna could be limited in some way.

Do you guys think it would be better for me to use this instead?

(RF Link 2400bps Receiver - 434MHz)

http://www.sparkfun.com/commerce/produc … ts_id=8949

(RF Link Transmitter - 434MHz)

http://www.sparkfun.com/commerce/produc … ts_id=8946

Maybe I could just use the above parts as a link with a small antenna and then just use a timer to buzz when there is no longer a link?

Thanks!

5

Yep, they are the parts I was thinking of.

Unless you pay good attention to the antenna design the typical range is maybe 20-30 feet. So it shouldn’t be hard to decrease the range.

Another way may be to use RFID devices. If the ‘tag’ can’t be interrogated then sound the alarm.

6

waltr:
Yep, they are the parts I was thinking of.

Unless you pay good attention to the antenna design the typical range is maybe 20-30 feet. So it shouldn’t be hard to decrease the range.

Another way may be to use RFID devices. If the ‘tag’ can’t be interrogated then sound the alarm.

I checked into RFID and Im not sure if it works for my application. See, what Im actually tying to do is build it into a USB flash drive so that it reminds the user that he/she is leaving it behind. So there will be a receiver on a keychain and a transmitter on the actual USB. I plan on running from the power of the USB port for the transmitter so 5V will be my supply. From what I hear for passive RFID system, 5V is not enough to wake up the tag at a 5 foot range. Correct?

7

I don’t know the details about RFID. Just throwing out the idea.

Since SFE does sell RFID parts hopefully some will post with the feasibility.