Brainstorm help with usb proximity project.

jsaenz210

Hi I'm working on designing and developing a device that will keep people from losing there usb drives by leaving them in a computer and walk away from them. My original idea was to have a simple unit consisting of a receiver held by a person and a small transmitter that would be attached to the usb via key chain. A signal would be sent from the transmitter to the receiver continuously or every minute or so. Once the person walks a set distance away from the transmitter (say 10m) the receiver would begin to beep and remind the person about their usb device in the computer.

I began researching the object sensors offered from parallax and my first idea was to use the ping ultrasound distance sensor as the transmitter and use a receiver to register the frequency of the sound from the distance sensor and extrapolate the distance based on the time intervals of the sound.

My second idea was to use bluetooth signals as a way of identifying distance. the bluetooth transmitter would send out a signal every 30 seconds. Once the person walks away from the bluetooth range (roughly 10 meters) the receiver would no longer register the signals from the bluetooth device and begin beeping and alert the user.

As you can tell I am very new to using this kind of technology but i just received my first Boe-Bot Robot in the mail along with a few basic manuals on sensors and I am very excited to begin learning how to use this technology.

I'm open to any and all comments or improvements on my method of approach on this project.

Mike Green

Using Bluetooth is a good idea. The "receiver" would attempt to link to the "transmitter" once every 30 seconds. If it succeeds, it would shut down the connection. If it fails, it would beep. You could also use xBee which is similar to Bluetooth. The main problem would be power for the "transmitter" since that would have to be on continuously since there's no way to know when the "receiver" would attempt to connect. Where would you get the power?

Using some other type of RF link might use less power. Other ideas if you could handle a shorter range might be IR. 10m seems like quite a bit of distance. 3-5m would work better for lower power technologies (like IR). Could the beep come from the "transmitter" attached to the USB drive? That way, the person could pin a small, low power IR beacon to themselves and the detector would be attached to the USB drive.

jsaenz210

what kind of power source would bee needed for the xbee and bluetooth technology? I know it would have to be external and replaceable but how large? Would it require something as large as a 5v batter or would a small power source such as a watch battery be enough?

Do you think it is possible to create a sort of wristband with the IR beacon attached so that it could be worn instead of pinned. I just think it would more convenient for people to put it on and not have to worry about it. Doesn't IR work with line of sight? If the IR beacon did not have a line of sight to the detector (usb being connected to a CPU underneath a desk or table) wouldn't that cause the detector to go off?

If that's not the case then IR technology seems like the way to go for me.

Mike Green

Read the datasheets for the devices you're considering. They'll give you the supply current needed.

Read the datasheets for the batteries you're considering. They'll tell you what the current capacity is (in mAh - milliAmp hours)

I suggested a pin because people let their wrists hang where cubicle walls or other barriers can more easily block the IR. Consider a flashlight. It's line of sight, yet can illuminate objects and walls. IR is the same except some surfaces reflect or absorb IR better than visible light.