A photo eye will be used to detect the traveling sprinkler. The Photo eye that will be used is numbered 42RP-604 and is made by Electronics Corporation of America. This particular photo eye is a PNP or sourceing photo eye. This means that the photo eye needs a power source in order for it to output a voltage drop when an item is passed in front of the unit. The photo eye that is used in this project is show as Figure 1.
How the Photo eye Works
The photo eye has 3 leads. The white lead is
connected to 12 VDC and the black lead is connected to ground. The orange
lead is the lead that will send a signal to the control system. For this
particular application two resistors were used to make the orange lead
output 5 VDC. When an object crosses in front of the photo eye the voltage
being outputted by the photo eye drops to about 0.9 VDC. This voltage is
inputted into an inverter at pin 1 (Data
Sheets for 74LS04), which makes the inverter output about 0 volts to
the flip-flop and turns off the solenoid valve. Figure 2 shows a schematic
of how to power the photo eye.