Multi-Tool Project: RF Tape Measure idea help

Projects General Guidance
1

I'm in the brainstorming phase of a project to make and an all around Multi-Tool for my everyday or every other day projects. It will combine an array of tools and sensors that I usually use separately into a single (hopefully) device.

One of the tools will be a component that can measure distances. Like a tape measure but instead of tape it will use RF. I chose not to go the Ultrasonic route because not all the things I will measure will be up against a wall (i.e. a stair rails or the length of a car) or have something to reflect off of. The idea is to have a device that my Multi-Tool can send a signal to or receive a signal from and a derive the distance between the two. The device would need to be small enough (like maybe the size of a Playstation memory card or smaller) to be attached to or slide into the Multi-Tool. I would place the device on one end of whatever I am measuring and the Multi-Tool on the other and read the distance.
It needs to be able to read somewhere in the ball park of 50 ft with the accuracy of an inch or better. I'm not dead set on anything so far so if I need to lower my expectations or be more realistic then I will. I'm just not sure what is realistic.

I just need a little direction as I'm not quite sure which direction I should take or things to research.

The ideas I came across were:

  • Passive RFID system. This would be the best choice as it does not require batteries on the device itself and can easily meet my size preference. However, I understand the range limitations are dependent on how strong a signal my Multi-Tool can crank out. I'm not sure if this approach can reach far enough. Some source say it is possible but, it's unclear if it is achievable with arduino.

  • Active RFID system. Can I make a DIY tag that is small enough and meets the distance requirements or is there one that is relatively inexpensive prebuilt? (like <$10) I've heard of the OpenBeacon project but to buy a tag from them is $20 for the component and $30 for shipping...

  • DIY low power coin battery powered RX/TX. Perhaps the most feasible of the ideas, but I'm not sure if it can meet the size requirements. Basically my tool will send out and signal, the device would reply and my tool determines the distance based on how long the reply took. Do they sell things like this already prebuilt?

Any advice is welcome and better ideas certainly are!

2

Firstly workout the time required to send a signal to the transponder and return and then ask if yourself if Arduino can work quick enough to calculate the distance especially for short distances.

RFID will not work over long distance and still needs to be triggered.

Active RFID needs to be triggered to be able to get distance via time.

Weedpharma

3

Laser tape measures are pretty cheap now.

4

weedpharma:
Firstly workout the time required to send a signal to the transponder and return and then ask if yourself if Arduino can work quick enough to calculate the distance especially for short distances.

RFID will not work over long distance and still needs to be triggered.

Active RFID needs to be triggered to be able to get distance via time.

Weedpharma

Wouldn't the time the transponder takes to receive the signal and then send out the response create enough of a delay for arduino to catch up?

Edit: I could possibly even program in a one second delay and then just account for that in the distance calculation. Maybe?

jremington:
Laser tape measures are pretty cheap now.

That isn't very expensive but it requires a wall or something to bounce off of in order to determine the distance. As I mentioned in my post I do a lot of things that that isn't always an option. Thanks though. Plus, I'm trying to make this an all-in-one project. One tool to rule them all kinda thing.

5

Carry some aluminum foil or similar to make a reflective surface.

6

What is the speed of light?

For the minimum accuracy you want to measure (1cm, 1m whatever) how long does it take light (or radio waves) to travel that distance?

Can you measure that short amount of time (or 1.00000000000000 seconds plus that time?)

Then you might consider if the clock on the "reflector" device is also accurate to that many decimal places when it's adding the 1 second.