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Light Sensor
| Two photocells will be used in our circuit in order to detect light
intensity in the greenhouse. One will be allowed to easily "see" sunlight and
its contacts will remain open as dusk/dawn approaches. The second photocell will be shaded
so that its contacts will close at dusk or dawn faster than the first cell. Discrete
inputs from these sensors will allow our instrumentation software to determine when to
send signals to the one or both of the lights. For the two inputs from the photocells we will need to purchase relays that will switch from a 120vAC source to a 5vDC source in order to send a low voltage signal into LabVIEW. The need for this relay is due to the fact that the photocells we are using are specified to be used in 120vAC circuits and our signal into LabVIEW will be a low voltage DC signal. We are researching this item at present. |
Logic for Light Intensity within the Greenhouse
Photocell 1 (unshaded) |
Photocell 2 (shaded) |
20 watt bulb |
100 watt bulb |
0 |
0 |
0 |
0 |
0 |
1 |
1 |
0 |
1 |
0 |
(don’t care) |
(don’t care) |
1 |
1 |
1 |
1 |
table 1
figure 3