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A simple step-counter pedometer being held in someone's hand.

Pedometers

by Chris Woodford. Last updated: October 3, 2014.

How far do you walk in a typical day? You might be surprised at the mileage you clock up pottering round the house, nipping out to the shops, and strolling to work or school. Walking a little bit more is a great way to improve your health and fitness; for some people, this kind of exercise is prescribed by their physician as a way to lose weight or get well again after an operation. How can you keep track of your walking without measuring from a map? Simple! Just wear a handy little gadget called a pedometer that counts each step you make. Ever wondered how they work? Let's take a closer look!

Photo: A step in the right direction? Wearing a simple pedometer like this on your waist can encourage you to take more exercise. This one also has an alarm clock, stop watch, and calorie converter.

How does a pedometer work?

A diagram showing how walking involves a constant adjustment to maintain your body's center of gravity in the right position.

Suppose I give you the job of building a little gadget that will measure how far you walk in a day. Sounds like a tricky task to me. You could use something like a click wheel (a large wheel you roll over the ground that clicks each time it turns one complete circuit), but rough or muddy ground is going to cause problems and it's going to have a job measuring stairs.

Okay, so let's redefine the problem by considering what walking involves. Every time you walk, your body tilts to one side and you swing a leg forward. Then your body tilts the other way and you swing the other leg forward too. Each tilt of the hips and shift of the legs is a step. Assuming each step is pretty much the same length, all we need to do is count the number of steps we make in a day, by counting the number of times our body tilts from side to side. We can then multiply the number of steps by the length of each one to figure out the overall distance walked. This is pretty much how a pedometer works.

Photo: Pedometers can measure your steps because your body swings from side to side as you walk. Each swing counts as one step. Multiplying the number of "swings" by the average length of your steps tells you how far you've gone.

Mechanical pedometers

Early pedometers were entirely mechanical and they worked a bit like pendulum clocks (the ones with a swinging bar powered by a slowly falling weight). As the pendulum rocks back and forth, a kind of see-saw lever called an escapement flicks up and down and a gear wheel inside the clock (which counts seconds) advances by one position. So a pendulum clock is really a mechanism that counts seconds. The original pedometers used a swinging pendulum to count steps and displayed the count with a pointer moving round a dial (a bit like an analog watch). You fixed them on your waist and, every time you took a step, the pendulum swung to one side then back again, causing a gear to advance one position and moving the hand around the dial.

Electronic pedometers

Animated illustration showing how a pedometer works.

Modern pedometers work in a very similar way but are partly electronic. Open one up and you'll find a metal pendulum (a hammer with a weight on one end) wired into an electronic counting circuit by a thin spring. Normally the circuit is open and no electric current flows through it. As you take a step, the hammer swings across and touches a metal contact in the center, completing the circuit and allowing current to flow. The flow of current energizes the circuit and adds one to your step count. As you complete the step, the hammer swings back again (helped by the spring) and the circuit is broken, effectively resetting the pedometer ready for the next step. The pedometer shows a count of your steps on an LCD display; most will convert the step count to an approximate distance in miles or kilometers (or the number of calories you've burned off) at the push of a button. Note that in some pedometers, the hammer-pendulum circuit works the opposite way: it's normally closed and each step makes it open temporarily.

Artwork: In this common design of pedometer, there's an electric circuit inside (red path) that is alternately broken and completed as you make steps. When the pedometer tilts to the left, the circuit is completed and a step is counted by an electronic circuit (top left). When it tilts the other way, the circuit is broken and reset ready to count the next step. Note how the hammer becomes part of the circuit: it has an electrical contact at one end wired to the circuit by a light metal spring (zig-zag red line). Other pedometers work in different ways, but most of the cheaper ones use a moving hammer and interruptible circuit in broadly the same way.

Pedometer app for the Apple iPod Touch and iPhone.

More sophisticated pedometers (including some of the really good ones made by Omron) work entirely electronically and, since they have no moving parts, tend to be longer-lasting, more reliable, and considerably more accurate. They dispense with the swinging pendulum-hammer and measure your steps with two or three accelerometers instead. These are microchips arranged at right angles that detect minute changes in force as you move your legs. Since accelerometers are often built into gadgets like cellphones, it's increasingly common to find these sorts of things offering to count your steps for you too (there are plenty of pedometer apps for the iPhone, for example). GPS satellite navigation devices can also figure out how far you've walked or run, but they do it by calculating from satellite signals rather than counting steps.

Photo: There are lots of pedometer apps for cellphones that make use of built-in accelerometers. This one's called Pedometer 24/7, runs on the Apple iPhone and iPod Touch, and seems to get good ratings from its users. As you can see here, it displays steps, average speed, total distance, and calories burned. You have to key in your height and weight to start, to give it a rough idea how long your steps are, and you can fine tune the sensitivity as well.

How accurate is a pedometer?

Counting steps with a pedometer sounds super-scientific, but you need to remember that it's only an approximate measurement. Not all your steps will be correctly counted and some false movements (jolts in the road as you ride in a car, for example) might be counted as steps too. Don't take the count too seriously; assume that it's in error by least 10 percent (the best electronic pedometers claim 5 percent accuracy).

For a pedometer to work correctly, you need to fix it to your waist—and not put it in your pocket—because a pedometer needs to detect the side-to-side tilting motion of your body to register each step correctly. Most devices come with a belt clip, making it reasonably easy to attach them properly. Some pedometers have a screw you can turn to alter the tension of the swinging pendulum-hammer inside them so it will register your steps correctly. If you're running, you might need to adjust it slightly differently compared to walking, for example, because your steps will likely be a different length.

How does a mechanical pedometer work?

A typical mechanical pedometer using gears and a swinging pendulum, from the 1904 US patent of Bartel and Kuhn.

Inexpensive modern pedometers are partly mechanical (they register steps using a swinging pendulum) and partly electronic (they use microchips to count the steps that the pendulum detects); early pedometers were entirely mechanical—so how did they work? Here's a drawing of the inside of a typical pedometer dating from a century ago. It was invented around 1903 by Otto Bartel of New York City and Edmond Kuhn of East Orange New Jersey and patented on April 26, 1904. I've colored the drawing and simplified the labeling so you can see how it worked:

  1. A pointer and scale at the top helps you adjust the pendulum accurately.
  2. A weight (red) at the end of the pendulum (blue) ensures it swings back and forth by a measurable amount.
  3. The pendulum swings as you walk. On this diagram, the pendulum would move up and down but, in reality, it would hang downward way and swing from side to side.
  4. The swinging pendulum turns various gears (green), advancing a pointer that indicates your step count (not shown).
  5. A spring keeps the pendulum tight. The spring is part of the adjustment mechanism for different step sizes.
  6. The pendulum swings about this pivot (purple).
  7. This large screw is also part of the adjustment/regulation mechanism for different step sizes.

Artwork: From US Patent #758,405: Pedometer by Otto Bartel and Edmond Kuhn, courtesy of US Patent and Trademark Office.

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Text copyright © Chris Woodford 2010, 2012. All rights reserved. Full copyright notice and terms of use.

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Woodford, Chris. (2010) Pedometers. Retrieved from http://www.explainthatstuff.com/how-pedometers-work.html. [Accessed (Insert date here)]

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