3-axis accelerometer
It’s a very simple design based on ADXL335 accelerometer chip from Analog Devices. The PCB has only one layer. The header output is provided for power input and X, Y and Z axis analog voltage representation of respective acceleration. A PDF schematic is also there if somebody is not a Diptrace fan 
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The circuit is used in many AC current sensing applications. Basically current is sensed with a 10A current transformer (called CT) and it’s signal is rectified through precision rectifier. The output is DC voltage which is then fed into MCU ADC.
This circuit, along-with voltage sensing circuit, can be used to measure power. For example it may be a part of intelligent power socket which measures the power running through an attached load. The intelligent power socket can shut down (turn off itself) on pre-programmed power outage or current threshold. The power socket may also inform a remote unit about the power status, periodically or upon request.
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The power supply change-over circuit is used where both Mains supply as well as power from rechargeable battery cells are used. The circuit, in normal mode, lets the power to be supplied from Mains to the circuit. When there is no input power, it switches on the supply from battery cells. When the input power resumes, it again cuts down the supply from battery cells and resume charging. Very simple but useful circuit.
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NiCd charging is a bit tricky and MAX712 is designed for that purpose. However, through experience I came to know that even after using charging chip, the resistor, capacitor or other components’ values are to be chosen very carefully. Below circuit is designed and test for 12 NiCd cells which makes around 14V4.
This circuit has been tested and used in active designs. The charge time to backup time ratio is very impressive.
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This circuit was used in product to save NiCd battery from being depleted. The circuit shuts off the supply from the battery to load and it resumes the supply once the input power resumes.
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MicroSD has been and still it is a very useful and cheap media to store data. Attached schematic shows how to interface it with any MCU via SPI interface.
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LM2576 is a very efficient switching regulator. It can supply upto 3A current with input range upto 60V (HV devices). It remain cool despite heavy loads and is very reliable. Diptrace and PDF files to download.
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MC34063 is a very popular switching regulator. The good thing is that it is very cheap as readily available. Diptrace and PDF schematic below.
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Flash memory is useful for data storage. Below is the circuit for interface with SPI flash memory products.
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Controller area network driver circuit using MCP2551 chip. Diptrace and PDF schematic files.
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