Page 84 - The Basics IA by ETron Circuit Labs

ETron Circuit LabsAdvanced Builds 2Moisture DetectorTheory:This project uses the 555 Timer IC as a “clock” with the frequency controlled by the amount of resistance between the probes. The lower the resistance the more it blinks per second. By experimenting with different soils you will get used to reading the results. With practice, you will be able to tell the approximate amount of moisture by observing the blinking LED.Procedure:Assemble the circuit and connect a 9-volt battery to the Battery Snap and observe that the LED may or may not be on. If you touch the probe wires together or put them into water, the LED will blink. The more moister, the faster the blinking. When you are testing plant soil for moisture, the more moisture the faster the blinking.DC to DC Power SupplyTheory:This circuit is a transistor with a potentiometer in place to adjust the bias on the base/collector circuit. By adjusting the bias with the potentiometer, you are able to get an output from 0 volts DC to 9 volts DC.The LED across the output lets you know that there is voltage. The resistance across transistor Q1 is varied with the potentiometer. When the resistance across Q1 is high, there is no voltage at the output. As you lower the resistance across Q1 with the potentiometer, the voltage increases at the output of the power supply. This is a DC to DC power supply.Procedure:Assemble the circuit and connect a 9-volt battery to the Battery Snap and you should see the LED light up. By using a multimeter at the output, you should be able to adjust it from 0 to 9 volts. This is an excellent project to power projects that require from 0 to something less than 9 volts.Railroad LightsTheory:This project uses the 555 Timer IC as a “clock” with a 50% duty-cycle. This means that the amount of time Pin 3 of the 555 Timer IC is HI is the same amount of time it is LO.You will notice that LED 1 and LED 2 are on about the same amount of time.The speed of the “blinking” can be adjusted by changing the values of R1, R2, and C1. But, as you change these values, you will also change the duty-cycle unless you maintain a certain ratio between the values. The formula for changing these values is available on Lab 15.Procedure:Assemble the circuit and connect a 9-volt battery to the Battery Snap and you should see the LEDs lighting up, once after the other, like a Railroad Crossing.82