Physical Electronic tape (or string!) measure, is there a sensor for this?

Hi I'm looking to add to an Arduino uno project a way of measuring distance, i have played with Ultrasonics and the Sharp IR sensor (which was a lot better) but I need a physical tape, string, cord that can be pulled out and will self wind back in that will allow me to measure the distance ever 100ms (200ms at a push) and ideally be accurate to +/- 1mm (+/- 2mm may be ok).

Googling i have found physical tape measures with Digital readouts and "Smart String" which is the sort of thing i would like to add to my project. any idea how these work and what the components are called and if they can be purchased?

thanks

Hi, if you are looking for a physical medium to use as your measuring device over that distance with that accuracy, then you will have to take temperature into account.

The medium of steel or any plastic will have a co-efficient of expansion, and it will be maximum in the direction you want to measure.

Even surveyors tools have specs that quote temperature when declaring calibrated distances.
Why do you need such high resolution/accuracy for?

Tom… :slight_smile:

Milliseconds?

hi Tom, the actual distance i will be measuring will be in the range of 10cm to 107cm i didn't thing +/- 1mm or 2mm was that precision! I may be able to get away with more. as for the time every 100-200ms if that is a problem i could just take an end reading. what i'm hoping to do is measure increasing resistance (weight) over time and distance. the overall time span is around 2 seconds .

I have an HX711 and i'm able to measure the resistance over time so now want to add distance. the IR is variable, even averaging the result and the aiming point is lost due to the free movement of what's being measured!

Thus if i attach a "string" and it is pulled out it should remove the aiming issue. but how do these digital tapes work?

I assume they have a rotating disk with slots that are counted, but i would need to buy the assembly and can't find any, only in products like the "magic sting" which would be ideal...

Thanks

hi Ken, yes ms = milliseconds

I_Need_Help2: hi Ken, yes ms = milliseconds

Ah sorry, I misread "ever" as "over", whereas you meant every :)

Hi, yes thought.

distance ever 100ms (200ms at a push) and ideally be accurate to +/- 1mm (+/- 2mm may be ok).

over 100 to 200 meters.

milliseconds == mS

So you are making a machine to do stress and strain measurements. Used one in University, materials lab.

Tom........ :)

Hi Tom, sorry if my description is confusing!

I'm look to measure a distance range of 10cm to 107cm the object takes around 2 seconds to move this distance and I would like to sample the distance moved ever 0.1 of a second (100ms), but every 0.2 seconds would be ok.

its not 100 - 200 meters!!!

Millisecond SI unit is quoted as ms not mS http://www.ewh.ieee.org/soc/ias/pub-dept/abbreviation.pdf and http://en.wikipedia.org/wiki/Second

I_Need_Help2: I would like to sample the distance moved ever 0.1 of a second (100ms), but every 0.2 seconds would be ok.

You're doing it again!

THE WORD IS EVERY

:)

Hi, no problems, I use mSec.. Tom... :)

oops sorry Ken!

You are Looking for a "draw wire encoder"