We are somewhat spoiled because electronics today are very reliable compared to even a few decades ago. Most modern electronics obey the bathtub curve. If they don’t fail right away, they won’t fail for a very long time, in all likelihood. However, there are a few cases where that’s not a good enough answer. One is when something really important is at stake — the control systems of an airplane, for example. The other is when you are in an environment that might cause failures. In those cases — near a nuclear reactor or space, for example, you often are actually dealing with both problems. In this installment of Circuit VR, I’ll show you a few common ways to make digital logic circuits more robust with some examples you can run in the Falstad simulator in your browser.
[Logi.cals], a German software company focused on process, automation, and facilities planning has devised an automated wine decanting machine to demonstrate its logi.CAD 3 PLC programming tool. Sommeliers use these simple machines to handle heavy, expensive bottles of wine. [Logi.cals] added sensors and a stepper motor to a very nice looking specimen and automated the decanting process with a Raspberry Pi.
The outstanding feature of this design is the built-in redundancy. A pair of micro switches detect the presence of both a bottle and a glass. Failing these, a load cell is there to weigh the bottle, reporting naturally whether one is present. The load cell also plays a part in monitoring the liquid level in the bottle, as do capacitive sensors that register the wine flow. The design also includes strain gauges that measure the weight in the glass as well as the liquid level. To bring it full circle, they also verify that a glass is present.
[Logi.cals] used two expansion boards, the Quick2Wire interface with an I²C analogue board and the PiFace. The I²C analogue board takes information from the strain gauges over its ADC, and the Quick2Wire communicates with the load cell’s measurement amplifier over the serial connection. The PiFace handles the remaining sensors and the stepper motor, and provides high voltage protection for the Pi.
If you’re fresh out of heavy, expensive bottles of wine but have some cheap ones lying around, you could use a Pi to make them dance.