Pump Controller with Liquid Level Detection

The circuit described here lets you control a cellar drainage pump so that it turns on when a preset liquid level is reached and turns off again when a different preset level is reached.

Two ingenious circuit configurations for RS232 half-duplex communications using just two wires.

Many robotic applications require a sensor to measure light levels. The conventional approach as shown in Figure 1 uses an A/D converter to measure the voltage drop across resistor R1 produced by the photo current through a photo transistor. The fixed value of R1 limits the light range which can be measured; a high resistor value is suitable for measuring low light levels while a low resistance is good in bright conditions. The resolution of the A/D converter also plays a part in determining the range of light levels that can be measured.