Some senses for Rino
One of the targets on an explorer competition is a gas source. This is obtained putting some alcohol in a container under the floor that evaporates slowly. The Figaro TGS822 gas sensor has high sensitivity to organic solvent vapors such as ethanol. It is composed by a semiconductor element that, in presence of detectable gas, increases it conductivity proportionally to the gas concentration in the air. The sensor works linearly only at a specific temperature, obtained with an heater that wastes most of the power, for this reason a dedicated voltage regulator is used on the sensors board. It requires some minutes after power on to begin working linearly.
On the board placed in the lower part of the platform there are two gas sensors to increase the size of the exploring area. The signals from the sensors are mixed in one output only with two diodes and connected to an ADC input of the MAX127 IC, so only the higher one triggers the detecting circuit. When the level goes over a threshold the robot stops for some seconds and light up a red LED to show that the goal is reached.
Schematic diagram for the lower board. On the same board are connected the optical switches for the bumpers and some components needed for signal conditioning.