Input
Sensors + Voltage Dividers
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The Input Sensor is part of a Voltage Divider (Potential Divider). This circuit often connects to a transistor in the next Process stage of an electronic system. The transistor then controls the Output(s) of the system eg. buzzer, motor etc. Adjusting the Voltage Divider Circuit A single transistor requires a 0.6 volt input signal from the voltage divider to turn on outputs connected to it. The Darlington Pair transistor requires 1.2 volts. To get these transistor "switching-on" voltages, you need to adjust the preset variable resistor connected to your sensor in the voltage divider circuit. To do this, connect a volt meter between the negative side of the battery and the middle of your voltage divider. In the example of a light sensor: when you experience the required level of brightness needed to turn on the output device, adjust the variable resistor to get the critical transistor input voltages, as described above (ie 0.6 or 1.2 volts). For more information on using a multimeter, see "Using a Multimeter" : Example: The Light Sensor
In our circuit below, when it gets brighter the resistance falls and when it gets darker its resistance increases. All the other sensors used in the FastTrack designer also vary their resistance as they detect a change in the surroundings (e.g. heat, touch, moisture etc).The other component in our light sensor circuit is the preset variable resistor. Its resistance value can also be changed (with a small screwdriver).
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The Voltage Divider In this circuit, both of the resistors divide or share the 9v input power supply voltage between themselves. The two voltages, seen across the components, will depend on their resistance values. Remember the two voltages must always add up to the battery/supply voltage (9v in this circuit). The "Voltage Out" will change when the light level on the L.D.R. changes or the variable resistor is adjusted. Use the above procedure to create the required voltage out for the required light level. |
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Other Voltage Divider Sensing Circuits
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