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# Ideas for Design: Vol. 1, No. 3

This round of Ideas for Design articles includes an encoder for direction signals, a spreadsheet that calculates 5% resistor values, an auto power conditioner without a power-hold relay, and a safe method for connecting transformerless supplies.

This round of Ideas for Design articles includes a direction-signal encoder, a spreadsheet for calculating 5% resistor values, an auto power conditioner without a power-hold relay, and a safe method for connecting transformless supplies.

Single-Chip Circuit Delivers Direction Information in Encoders

Incremental-rotation or linear encoders are very common, but normally they don’t provide a direction signal. This design shows an easy way to detect forward or reverse direction.

Excel Formula Calculates Standard 5% Resistor Value

When using a spreadsheet to calculate circuit values, determining “standard” component values for use in subsequent calculations can produce more accurate results. This approach will also result in real-life solutions to your circuit designs. When 5% resistors will suffice, this Excel solution provides values that can directly be used for a material list.

Automotive Power-Conditioning Circuit Eliminates Power-Hold Relay

Automotive electronic control applications require robust input power conditioning. The circuitry must absorb 100-V transients on the one hand, while providing a stable dc bus for a few hundred milliseconds after the ignition is switched off on the other, so that the CPU has the time to write logged data into EEPROM before going off. The use of high-energy transient absorbers usually meets the former requirement, while an electromechanical relay handles the latter.

This circuit offers novel solutions for both requirements. It replaces the costly and bulky transient absorbers with an electronic switch and the electromechanical relay with a simple RC timer that sustains the dc bus for a preset amount of time after the ignition is switched off.

Simple Strategy Safely Connects Transformerless-Supply Circuits

Low-power circuits commonly use transformerless power supplies. However, using earth grounds in many of these circuits creates a serious problem that’s often ignored. This design safely connects transformerless-supply circuits.