This lets you write and read byte values from an sd card. It’s very simple to use. The schematic uses some resistors in a voltage divider to drop down the arduino 5v logic to the sd cards 3v3 logic. So all outgoing signals from the arduino are dropped to 3v3. Incoming signals to the arduino are fine because 3v3 is above logic 1 for arduino. The 3v3 voltage supply from the decimelia was used to supply power to the sd card.
Interfacing SD Card With Arduino: [Link]
This circuit provides a constant amount of power to the LEDs and also provides a constant amount of light for a longer period of time. This circuit also allows the LEDs to run on almost any normal voltage above 4 volts. This means you can use multiple sources of power for the same light, a few AAA batteries, or even a car battery.
Constant Current Supply For LED’s: [Link]
Mobile infrared electronic transmitter
This project explains how you can build a very powerful wattmeter by using a simple circuit called AD8307. The author choose to make this wattmeter digital and the display showing the power in watts. A good wattmeter is very important for a hobbyist that is working with RF and transmitters, it will really make your work easier.
30 W Digital Wattmeter With LCD: [Link]
Lithium Ion batteries pack a lot of power by weight compared to other types. There are 2 things that need to be handled differently than nicad on NiMH:
1. They cannot be used as a direct substitute (even if they look like other AA’s) since they run at about 3.6 (or so) volts.
2. They cannot be charged in the same way as nicad or NiMH.
Sooner or later you are gonna need a Li Ion charger in one of your projects, so it’s better to be prepared.
DIY Lithium Ion Battery Charger: [Link]
Sometimes you need a simple negative power supply. The best example is the contrast PSU for common small LCD device. Building -5V from a battery or a wallmart supply isn’t really easy. The author used the MAX 764/765/766 series to build the power supply. You can simply change the chip to provide the desired output.
Negative Power Supply (-5V / -12V / -15V): [Link]
