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Circuits designed by David Johnson, P.E.
Last Updated on:
Thursday, March 22, 2012 06:41 AM
Master Category List
- Dave's Circuits
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Copyright © David A. Johnson, PE - ALL Rights Reserved.
LINKING to Dave's circuits is permitted but DO NOT COPY to your WEB SITE server! |
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Solar Cell Monitors |
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Solar
Insulation Monitor
An inexpensive PIN photo diode and a 1ma meter movement form a simple sunlight
intensity monitor. The sensor should be placed inside a lightly frosted
glass hemisphere to minimize the influence of the sun’s angle on the sensor.
An adjustment resistor calibrates the meter for a full scale reading under a
one sun condition. An unshielded two conductor cable links the sensor to
the meter movement. The sensor and meter can be separated by up to 200
feet.
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Solar Powered
Lithium Ion Battery Charger
This circuit is for a solar powered white LED with automatic activation in the dark. It
can be used for both indoor and outdoor night light applications. For indoor uses, if
the circuit is operated near another lamp, it can be set to automatically turn on when
the other lamp is turned off. Circuit features include selectable off/on/auto settings,
a built-in low voltage disconnect circuit for longer battery life and a light activation
circuit with hysteresis.
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Solar PV cell Test
Fixture
This is an illustration of a test fixture, which can be used to test individual solar
cells for short circuit current. Using a PIN photo diode and a control circuit,
the solar cells can be tested under constant light level conditions. A halogen
incandescent lamp is used as the light source. (added 7/06)
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Solar-Powered
Pump Motor Controller
A Discover Circuits visitor had a problem. He needed a simple on/off controller
for his solar powered water pump. His system used two 12v 50 watt solar panels
wired in series. The power from the solar panels drove a submerged water pump.
However, during overcast skies the pump motor did not operate properly due to the lack
of power from the panel. He wanted a circuit which would turn off power to the
motor during low sun conditions. The circuit below performs this function. A
small 0.1” x 0.1” photodiode monitors the sunlight intensity. The current from the
diode is proportional to sunlight intensity. An adjustable load resistor across
the diode converts the current into a voltage and feeds the to a voltage comparator
circuit. The output of the comparator drives a small n-channel MOSFET, which in
turn drives a high current p-channel MOSFET, controlling power to the pump motor.
When the sunlight is less than one fourth of full intensity, power to the motor is
turned off.
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Visible Light Blocking
Filter
This isn’t an electronic circuit but the drawing below shows the curve for an optical
filter made from exposed color film. The material blocks most visible light but is very
transparent to 880nM infrared light. Kodak 100ASA is exposed to "cool white" fluorescent
light for about 5 seconds.
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