Any hints on how to buld pedometer?

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samsmiles
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Any hints on how to buld pedometer?

Post by samsmiles » Thu Jul 31, 2003 1:01 pm

Hello everyone,
does anyone around here have any exp. in building pedometer or any hints.<p>Many thanks.
Sam

josmith
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Re: Any hints on how to buld pedometer?

Post by josmith » Thu Jul 31, 2003 4:08 pm

Get a cheap calculator that has an automatic constant function (most do). Enter your factor which will be the result of the length of one step divided by one mile.Press the + key.Have the step counting swith operate the = key.Miles will accumulate on the display.<p>The step sensor is usually some kind of pendulum driven switch or possibly a mercury swith.<p>Then again you could just buy a pocket GPS had have all the data in one place for every mode of transportation.

Will
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Re: Any hints on how to buld pedometer?

Post by Will » Fri Aug 01, 2003 9:56 am

The cheap calculator is a great idea ! I doubt that the GPS would be much use since I believe they are only good to about a 30 meter radius.
The cheap calculator could even be made to work on Mikea196's Cycle Speedometer by using a 555 and counter chip. Click the calculator and reset the counter each time a specific count was reached
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Re: Any hints on how to buld pedometer?

Post by rosborne » Fri Aug 01, 2003 11:47 am

I recently went to a seminar on GPS and just wanted to let you know that even a relatively inexpensive GPS ($150 US) is way better than 30 meter accuracy. I got this quote from Consumer reports.
"For years, GPS units had an accuracy problem caused by Selective Availability (SA), an intentional degradation of the accuracy of civilian GPS devices imposed by the U.S. Department of Defense so spies and terrorists couldn’t lock onto targets with any accuracy. The government lifted SA on May 2, 2000. As a result, the accuracy of GPS units has increased phenomenally; some units’ accuracy can be measured in inches, while most are accurate to within a few feet."
$150 is a lot of money to me, but at the seminar I saw a demo of someone carrying a civilian GPS unit along the lines of a tennis court and you could easily see the shape of the course.
-Rick

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haklesup
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Re: Any hints on how to buld pedometer?

Post by haklesup » Fri Aug 01, 2003 3:21 pm

Rick is correct, with SA turned off my recievers showed dramatic improvement in accuracy right away. That's one thing Clinton did do right. Generally the accuracy has to do with how many satellites the rcvr can see and how long you have been locked on. Military recievers use a more accurate signal called P code.<p>GPS for a pedometer function is great but a bit expensive (compared to a walmart ped for $20 to $30). The accuracy of the trip distance would be unsurpassed and some models also track altitude.<p>It would have the problem of blackouts when you are indoors or on a very shaded path or among tall buildings. It's also a bit bulkier and may not work as well from a location on your hip as it would on top of your head (so now you need an external antenna sewn onto your hat :) ). <p>Incedently the Garmin Gecko models have virtual games built in where you manuver through a virtual maze or look for virtual characters.<p>The calculator idea is great for counting or measuring anything where the increments are not whole integers. The trickiest part is in designing a reliable switch that pulses only once for each step. If a purely mechanical design turns out to be unsatisfactory you might try a 1 or 2 axis accelerometer chip.<p>Chris

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Re: Any hints on how to buld pedometer?

Post by Will » Sat Aug 02, 2003 11:26 am

Y'all may be right ? - Before SA was turned off stated 2 drms (The equivalent of two standard deviations) accuracy was 300 metres - Since SA has been turned off I thought it was 30 metres - I must try to check into it again. I don't think mine is that accurate but I have no way of telling unless I go and stand all day by a class A NGS monument. I frequently sail several hundred miles with a friend and his boat is fitted with a GPS which cost him $1,000 or so. It follows us OK but I remember that last year when we were in the Intracoastal, it followed us OK but for some of the time the positional arrow showed us as being just about one river width away in the adjacent fields. Errors tend to localised because of local conditions and it is conceivable that it could show a reasonable shape of tennis court - but would it display the latitude and longitude accurately ?
I also remember that, when I used to be part of a surveying crew our maximum allowable closure error for one day's surveying (During which we might cover 60 linear miles) Most times we made it but sometimes we had to go back and re-survey. The GPS equipment we used cost more than $20,000 per set and we had to have at least two sets.
I really need to get with it and find out more. Have fun!
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Re: Any hints on how to buld pedometer?

Post by Will » Sat Aug 02, 2003 11:30 am

I see that I moved in a helical direction again. In the part where I dwell on the surveying accuracy I should have said that the maximum allowable error for one day was one metre.
I had to type the whole thing twice anyway because my connection was severed when I first tried to post. Have fun
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Re: Any hints on how to buld pedometer?

Post by larussell » Mon Aug 04, 2003 8:23 am

30 meters (100 ft) is about right as a worst case error for GPS. That is the size of a standard U.S. suburban 1/4 acre lot, which I would think is close enough for use as a pedometer. As you acquire more satellites the accuracy gets better, down to 15 feet in my experience.<p>Surveyors use something called differential GPS. In this system, there are fixed base stations that receive the GPS signals and calculate error values based on where they really are vs what GPS tells them. (It turns out that GPS error values are fairly constant over a local area.) These error values are then transmitted to the surveyors' instruments which use them to compute location down to inches. A separate subscription based terrestrial radio link is used, which is why these systems are so expensive. There has been a proposal made to transmit the error values as part of the satellite GPS signals, which would mean every handheld GPS could receive them without special equipment, which would give everyone this kind of accuracy.

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Chris Smith
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Re: Any hints on how to buld pedometer?

Post by Chris Smith » Mon Aug 04, 2003 1:28 pm

Saw one advertised for less than 15 bucks?

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Re: Any hints on how to buld pedometer?

Post by Will » Mon Aug 04, 2003 9:58 pm

Good stuff nospam ! - Ive been away from surveying for a while but I don't believeb Differential GPS will get you down to inches - There are three principal types of differential which I know -they all need compatible receivers - The first are on some of the Coastguard beacons which are directional only radio transmitters. The selected ones are fitted with sereial coding devices which transmit the local errors. These are figured by each station knowing it own precise location and comparing this with the reading the GPS receiver gives. They are of course only precise atheir own location - the further you get away from them the less accurate the error statement. The service is free and the required receiver cost about $2,000 last time Iooked. They are still used by marine vessels becuase 30 metres is OK when you are out at ses but not quite so good for entering harbor in the dark.
The next level is a subscription service - it is transmitted over an FM radio service. The third, most costly is a fairly expensive, satellite broadcast, subscription service - you need their receiver and pay a significant monthly fee for access. You tell your receiver your rough location and it selects the correct info for you from the satellite broadcast.
The expensive ($20,000) receivers I referred to didn't contain or use differential. What we did was to go to areas which were to be seismically surveyed. We would go to each site, survey one point precisely and drive a monument with a tag number into the ground. We always had two have two stations in the chain operating simultaneously for at least 45 minutes and the receivers would store the data. After a 45 minute interval then you would leave the last receiver you place in position and move the second last one to the next position. Then the pair would have to receive for 45 minutes. You would start the day at a known NGS/government survey monument and finish at either another one or the same one of you had travelled a closed route. The the data would be processed each night using a standard PC with an advanced statistics program and determine the position of each surveyed station using the computed data from the last one. These precise positons would be passed to the survet crews next day so they would position a receiver on each monument we had placed a transmitter placed with each receiver would then transmit the errors to each field surveyor using a back pack Differential GPS Receiver and they would position each seismic point. Once you got to day's end then you had two positions i.e. the one you had computed from the last receiver in the chain and the actual monument position. If the two differed by more than one metre then they were not acceptable. This error was known as the closure error. If it was with the one meter then you could have confidence that all of your stations were within a few centimetres. This was all before SA was removed.
I doubt that you will be able to buy a cheap hand held containing differential info direct from the satellites because they don't know where you are. Marine, survey and other users are now urging the government to transmit additional signals at different frequencies so that diffraction errors can be computed with respect to the frequencies.
There is another new form of expensive GPS receivers which I don't understand - they are called ? kinetic ? - I don't know how they work but they will not produce the accuracies described above. Have fun!
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haklesup
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Re: Any hints on how to buld pedometer?

Post by haklesup » Tue Aug 05, 2003 2:37 pm

Check out the may issue of GPS world online at the link below. There is an article about Kinematic GPS (KGPS) getting accuracies as good as 10cm. In essence they use accelerometers to provide dead reconing input to the controller while the GPS signal is obscured<p>Other issues also have articles about Surveying and just about any other GPS application you can think of.<p>http://www.gpsworld.com/gpsworld/articl ... p?id=57964

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Re: Any hints on how to buld pedometer?

Post by Megadan » Fri Aug 08, 2003 10:18 am

If you open up the February 2003 issue of our magazine, the winning entry for the TI MSP430 design contest was a multi-function accelerometer. One of the functions was a pedometer.<p>Dan
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samsmiles
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Re: Any hints on how to buld pedometer?

Post by samsmiles » Sun Aug 10, 2003 6:54 am

Thanks a bunch everyone!!!
Dan I checked the ftp files for from nuts and volts. Awesome! I missed february issues but I got it from friend now :-). The merucury part seems very tricky ie the switch! Im not sure how stable it is with different people, different spet lengths, esp if you are walking up hill and downhill etc!<p>About gps systems I didnt think of it before I didnt know how exact they are plus the price tag seemed high.
BTW has anyone here tried to buld one? Siemens company is selling magnetic field sensors and signal conditioners to build gps. I dont know hwo exact those are but its interesting.
I have this odd wish to build myself system for my triathlon preps with pedometer, pulse meter, watch, etc... <p>Thanks again to everyone this board is real learning black hole for me NO END TO IT :-)<p>Have a great day!
Sam

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Re: Any hints on how to buld pedometer?

Post by joopv » Sat Sep 06, 2003 3:43 am

Sorry for the late reply...
You might be interested in the DIY GPS receiver kit i assembled around a Rockwell Jupiter GPS module.<p>Take a look at http://www.gpskit.nl/index-en.htm<p>Regards,<p>Joop - Eindhoven - Netherlands

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