All posts for the month January, 2013

Raspberry Pi Current SensorAfter constructing a solar panel and battery system to power a Raspberry Pi, I wanted to find a way to monitor how the battery and charger was performing.  There are several ways to accomplish this task, usually involving a voltage sensor, a current sensor, or both.

A voltage-based sensor can be used to monitor the charge of the battery.  Over a typical day, the battery voltage should rise as the solar panel charges the battery, and then discharge at night while the Raspberry Pi consumes power from the battery.  A common technique for monitoring voltage is to use a voltage divider.  If appropriate resistances are chosen for the voltage divider circuit, the drain on the battery from the sensor is negligable.

Another option is to use a current sensor.  A current sensor placed off of one of the battery terminals will measure how much current is flowing into or out of the battery.   Continue Reading

iceclockWhile browsing one of our favorite electronic supplier’s web sites, we found that Ladyada sells a really interesting looking clock that uses a vacuum florescent display with eight glowing digits.  This clock proved to be an excellent soldering instruction project for a younger Rusty Nail Workshop helper.

The most interesting feature is the display, which is similar to those found on VCRs, old car radios, and microwave ovens.  The vacuum florescent display was invented in 1967 in Japan and hundreds of millions are used annually around the world.  They are different than an LCD in that they use a filament to emit electrons which are diffused by grids.  The electrons strike a phosphor-coated plate and emit light, and can be manufactured to emit light in different colors. Continue Reading