Intervalometer

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An intervalometer is a device which measures intervals of time (interval-o-meter). Such devices commonly are used to signal, in accurate time intervals, the operation of some other device. For instance, an intervalometer is what you would use if you wanted something to be done every 30 seconds.

[edit] Photography

Intervalometers are used to trigger exposures of a camera at a defined interval, most notably for time-lapse photography. Intervalometers are also used to trigger an unattended camera, such as for aerial photography, where you want the picture(s) to be taken, or begin being taken, after a known period of time (e.g. 10.57 minutes after take-off/launch).

Most cameras have very basic intervalometer functionality, the "self-timer". A self-timer can be used to delay taking a picture for short time. The delay is commonly used for the photographer to get into the picture. A self-timer is so basic such that most people do not think of it as an intervalometer.

In the past, intervalometers were basic external devices which interfaced to a camera to trigger taking a picture, or series of pictures, at a set time. At this point, products commonly referred to as intervalometers have added capabilities far beyond the basics of just measuring, and signaling, a time interval. One of the first features that was added to intervalometers is the ability to use an external event to signal the start of the time interval(s). The ability to sense an external event is such a common feature of intervalometer products that many people do not distinguish between the sensing of the event and the measuring of time intervals.

At this point what is meant when someone refers to an "intervalometer" must be determined from context. It could be many different things. Some possibilities are: time-lapse capability (strictly an intervalometer function), sensing of a remote event, a time delay longer than what most consider the "self-timer" range, etc. Strictly speaking, an intervalometer only measures, and/or signals, time intervals.

Almost all digital cameras have the basic hardware capability (knowing the current, or elapsed, time) required for complex intervalometer functions. Intervalometer functions beyond the self-timer are beginning to be seen in some digital cameras. Given that the hardware capability is present in any digital camera that knows the date and time, the implementation of more advanced intervalometer functionality is a matter of what the manufacturer puts in the camera's firmware. Advanced intervalometer functionality will probably become more prevalent as a standard feature in digital cameras. Variable levels of intervalometer functionality are already being used as part of the differentiation between models within a camera line.

The CHDK project, started by Andre Gratchev, has successfully modified the firmware for many Canon PowerShot cameras. Among the many features added by CHDK is programmable intervalometer capabilities.

[edit] Non-Photography Intervalometer Examples

The ALE-39 countermeasures system uses intervalometers manufactured by Ledex Inc. (now part of Johnson Electric) of Dayton, Ohio. The ALE-39 can fire flares in a synchronized pattern, very rapidly and with great reliability. The intervalometer used in the ALE-39 is essentially a solenoid-actuated rotary switch driven by solid-state timing circuits.

One of the more common types of intervalometers is the timer that is used to turn lights on and off at set times. These are commonly used by people when they go on vacation. There are also a large number of commercial and industrial applications for even such basic intervalometers.