Gadget Freak

More inspiration for designing your own circuits - the three latest Circuit Design Ideas that have been added to the site. They involve harvesting energy using a piezoelectric buzzer, a retriggerable monostable multivibrator, and analog voltage controlling a digital potentiometer through the device's I2C interface.

Harvest energy using a piezoelectric buzzer, courtesy of Carlos Cossio, Santander, Spain

Retriggerable monostable multivibrator quickly discharges power-supply capacitor, courtesy of Jordan Dimitrov, Tradeport Electronics, Vaughan, Canada

Analogue voltage controls digital potentiometer, courtesy of Hrishikesh Shinde, Maxim Integrated Products, Dallas, USA

Harvest energy

Energy-harvesting, or "scavenging", systems extract energy from the ambient environment. Unfortunately, these power generators supply much less energy than do standard batteries.

However, thanks to the decreasing size and low-power requirements of today's wearable devices, it is feasible to replace batteries in some low-power systems with power generators that capture energy from the user's environment, such as the vibration energy a user produces during walking or running...

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Discharging the high-voltage filter capacitor

Universal power supplies must work from mains power lines ranging from 90 to 264V ac at 50 or 60 Hz. Directly rectifying the input voltage charges the filter capacitor to 120 to 370V dc. Such voltages present a serious threat to personnel who are prototyping or repairing the power supply. It is desirable to discharge the filter capacitor when mains power is off so workers can safely deal with the power supply. An intuitive solution is to use an ac relay.

However, relays cannot operate in a wide range of input voltages, they consume significant power and space, and they have a limited number of cycles...

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Controlling digital potentiometer

This Design Idea describes an analog voltage that controls a digital potentiometer through the device's I2C interface. An ADC in the Microchip PIC12F683 microcontroller converts the analogue voltage to the I2C stream that controls the Maxim DS1803 digital potentiometer.

Of the microcontroller's six general-purpose I/O pins, two control the SDA (system-data) and SCL (system-clock-line) output signals, one controls an LED, and one accepts the analogue input. SDA and SCL connect directly to the digital potentiometer's SDA and SCL pins with 4.7-kO pullup resistors to VDD. By adding or removing jumpers, you can separate the shared VC and VDD and isolate SDA and SCL...

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Check out the full Design Ideas section of Electronics Weekly