This very simple timer circuit can allow data loggers (and other devices) to operate for many mon...
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This very simple timer circuit can allow data loggers (and other devices) to operate for many months on small batteries. The timer supplies power to the device only at the desired interval, so between data logging events only the timer uses power. The timer itself consumes very little power (30µA), so batteries last a long time. Assembling the timer involves soldering three components to a little printed circuit board (PCB). The data logging interval can be set between 5 and 110 minutes.
This timer works well with data loggers based on 3.3 volt Arduinos like the Mini Pearl Loggers. The low-power TPL5110 cannot tolerate more than 5.5 volts, so five volt Arduinos (which like to get about 6 volts) are harder to use with the timer.
When the logging event is complete (e.g., data is written to an SD card) the sketch on the Arduino signals the timer circuit to cut power. Until the next logging event, the Arduino logger is turned off and uses no power. When the timer again supplies power to the Arduino, the sketch begins to run and instructs the logger to collect data from sensors, do calculations, save data to an SD card, etc., and eventually sends a signal back to the timer to cut power again.
Above: The parts included in a Log-a-Long Timer Kit. A selection of five surface-mount resistors (bottom) allows one to be chosen for the desired logging interval. Ruler hatch marks are mm.
Header pins are not needed if the five wires to the battery and data logger are soldered directly to the pin holes. Header pins allow DuPont wires (not included in the kit) to slide on to make the connections.
Above: Build diagram for the Log-a-Long Timer Kit. Three components and five wires must be soldered to the green PCB.
Above: A Log-a-Long Timer (left) controlling a Mini Pearl Logger.
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