- Cheap Close-up Camera Lens
I often use my digital camera to take photos of some electronic projects. At times, I need to get in close to capture some details. But, without some additional optics, my camera just could
not maintain focus, as I got closer to an object. Being a cheap person, I didn’t want to spend money on an expensive close-up lens...
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- Homemade Corner Cube Reflector Using Glass Mirror Tiles
Corner cubes are optical devices which have a unique property. Light sent into the front face will be sent back to the source in a parallel path. As long as light can strike the
reflective surfaces the it will always be sent back to the source. Tiny corner cubes can be molded into plastic for form an array of individual reflectors. These are often used
on bicycles to make them stand out at night....
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- Pigeon Scarecrow
I have an area on my roof where a large flock of pigeons like to roost. Their nesting materials and droppings really make a mess. Often there is enough junk from them that it clogs my
roof gutters. Perhaps one way to scare them away is with a device mounted on the roof near their favorite roosting spot. The device....
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Modified LED Night Light
NEW
The circuit uses the classic series capacitor method to produce a current limiting LED driver, powered from the AC line. The series capacitor
forms a constant current source and will route the same amount of current through the parts, even if 3 or 30 LEDs were used in series. This type of circuit made it much easier to
insert 10 series wired LEDs instead of the three original devices. I also switched from a NPN darlington driver circuit to a single n-channel FET. This made it easier to select the
right resistor value to turn off the light in the day. I set the required CdS cell resistance at about 100K, so anything less than that in resistance should keep the LEDs turned off.
I did have to change the resistor R2 to a 39v zener diode, to limit the peak voltage across the filter capacitor C1, when the LEDs are turned off during daylight.
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Shake to Charge Flashlight
NEW
The complete schematic for this device is shown below. A few things should be pointed out. First, they use some very cheap 1N4001
diodes in the bridge rectifier circuit instead more efficient Schottky diodes. They also use a small 0.5 Farad cap with a 5.5 volt rating. I noticed that that this kind of super capacitor
was originally designed for maintaining data in memory chips and has a rather high internal equivalent series resistance. This reduces the overall efficiency, since the device can’t be
charged or discharge very quickly. Some of the power that should go to the LED will end up being dissipated inside the capacitor. Better super capacitors do exist.
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- Ocean Wave Power Generator Demo Unit
A while back, a Discover Circuits visitor wanted a simply way to demonstrate how electricity could be generated from the up and down movement of ocean waves. The system was to be part of a
science fair project, showing different renewable energy sources. I gave this some thought and came up with the system shown below. It uses a simple plastic foam float attached to a
lever arm,...
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- Worm Harvester
When I was a kid my engineer uncle built a circuit similar to the one below. My cousin and I used it to force earth worms out of the ground to be
used for fishing. It worked like a champ. Please be careful since there is high voltage at the probe tips.
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