Chronograph Watches

Chronographs are watches that combine two or more time functions. Originally they were developed to measure elapsed times, such as how long it took an athlete to run a certain distance or how much time has elapsed in a car race. Nowadays chronographs measure not only hours and minutes but also seconds, and even tenths of a second (the most accurate recordable intervals).

Most watches today are powered by a battery. Solar powered watches save you the trouble of replacing batteries and cost less than those that rely on electricity from the grid. Quartz analog watches use quartz crystals instead of mechanical parts to regulate their timing; so there is no need for winding them up or manual adjustments to keep them running accurately.

To show you how a chronograph works, let's build our own. Theoretically we could have used a digital counter to measure seconds, minutes and hours. But since it's not available for experiment, we'll use an analog quartz watch with two dials instead.

A typical analog chronograph has three dials and the following arrangement:

The total elapsed time (power reserve) indicator . The elapsed time already passed is displayed from left to right along the top of the dial; then it winds down from right to left at a rapid rate. We'll call this the "time elapsed indicator".

. The elapsed time already passed is displayed from left to right along the top of the dial; then it winds down from right to left at a rapid rate. We'll call this the "time elapsed indicator". A central chronograph hand , or "chrono hand", that measures seconds, minutes and hours (from right to left). We'll call this the "chronograph hand".

, or "chrono hand", that measures seconds, minutes and hours (from right to left). We'll call this the "chronograph hand". An external elapsed time indicator . On most modern watches, it has a 24 hour scale just like a clock. Because it's less frequently used, it's often on the right side of the dial. We'll call this the "external time indicator".

. On most modern watches, it has a 24 hour scale just like a clock. Because it's less frequently used, it's often on the right side of the dial. We'll call this the "external time indicator". A sub-dial at 12 o'clock that tells you what function is being used at a glance: reserve power , chronograph hand or external time indicator .

We're going to build a mini-chronograph that only has two functions: reserve power and elapsed time (we lack space for an external time indicator). Here's the schematic diagram:

This is our basic chronograph. But it's not complete. We'd like the reserve power indicator to be a counter that counts down from 24 hours – much like the time elapsed indicator counts down from 60 minutes. To do this, we'll add a single transistor:

Now we have a working mini-chronograph. The interesting thing here is that you don't need a microprocessor to build a digital chronograph. It's all possible thanks to basic electronics, such as counters and transistors.

If you've built the circuit I've shown above, you'll have noticed that it does not have an external time indicator (the central hand is used for this purpose). You might want your chronograph to have just one function: external time indicator. If so, add an additional transistor and resistor as follows:

Now we're ready for our first experiment. We can use this circuit to measure elapsed time. We'll build a miniature race clock and mount it on the chronograph dial itself.

Here's what we need:

One 12V battery with some extra capacity (for example, two 2032 button batteries). A quartz watch that can last up to 40 hours on reserve power (a cheap sport watch will do fine). Transistors Q1, Q2 and a 10K resistor (1/4 watt). A 3-way switch or "pace switch" that allows you to choose between reserve power, chronograph hand and external time indicator.

This is what we end up with:

It's a miniature race clock! (The switches are hidden behind the dials, but the wires go through these holes.) The 12V battery powers the entire circuit. The watch switches between reserve power and chronograph hand on demand. This works because of the transistor Q1, which is wired as an analog switch. It routes the current from the battery to either the quartz watch or to Q2 (the pace switch). When you press pace switch B, it enables quartz watch mode so you can see how long your competition will last on their energy reserves.

When you push switch A, it enables chronograph hand mode so you can see exactly when your opponent crosses the finish line.

To give yourself a head start, you can run along the track in advance (there are two wires for pace switch A). Pace switch B is good for up to 6 hours of reserve power. When it runs out, press pace switch A again to kick-start the race!

Here's what our miniature chronograph looks like on the dial:

You can modify it in many ways. For example, you can mount a temperature sensor around the track so that it measures ambient temperature with every lap. Or add a GPS module to show your exact position and distance travelled round the track. You can put a buzzer on the circuit to alert you when the race is about to start. You can build a solar or kinetic chronograph with hands that don't require battery power. The possibilities are endless!

And if you're looking for more electronics projects, check out my book from O'Reilly: Practical Electronics for Inventors. There's even more things you can make, including an FM stereo decoder and an automatic gate opener! So have fun and keep checking into tronixstuff.com .

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Conclusion:

Thanks for reading this post, and be sure to experiment with your own circuits. I've got a number of other electronics projects that involved some simple components and wiring. You can also checkout my arduino project ideas page here on TronixStuff. And if you're interested in learning more about the basics of electronics, be sure to check out my beginner's guide "How to Read a Circuit Diagram" !

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