Author Archives: R-B

AC load dimmer using triac

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Triacs-based dimmers are based on the principle of controlling the phase of AC voltage applied to the load and are specially designed for resistive loads such as incandescent or halogen lamps. Mike from Electronics-Lab has shared this simple TRIAC AC load dimmer circuit that can handle AC power up to 400VA. The circuit is working by controlling the phase of the 220 VAC voltage allowing the load to be powered for less than 360º of the full sine wave. Powering the load for smaller period than full sine wave delivers less power, so it has a dimming effect on the load.

AC load dimmer

DIY mailbox alert system that texts you when letters arrive

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Here’s a DIY mailbox alert system that will free you from guessing, wondering, or making wasted trips to the mailbox only to find it empty. Yes, this Arduino-based mailbox notifier sends you a text whenever you get mail. The device uses a simple light-dependent resistor (LDR) to detect the light levels inside the mailbox. When somebody opens the mailbox, the light level goes up and Arduino knows it is time to send a text. It can also serve as a security device to avoid your mail being stolen if the mailbox is accessed during non-delivery hours. A push switch button at the front of the device is used to arm or activate the sensor. Once the sensor is activated, the next time the mailbox is opened, a text message is sent to your cell phone. It will not send any text again until it’s armed again. This ensures that you don’t get a text every time you open the mailbox. So, a good practice would be to arm the sensor system every time you go pick up your mail.

Mailbox alert system

Proximity sensing for mobile phones SAR requirements

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Research in to the long term health effects from exposure to radio frequency energy has been ongoing over the past two decades. As a result of this research the FCC and other telecommunications agencies have adopted limits for safe exposure to radio frequency (RF) energy. These limits are referred to as the Specific Absorption Rate (SAR), which is the measure of the amount of radio frequency energy absorbed by the body when using a mobile phone or other wireless device. The FCC and other agencies require that manufacturers of wireless devices comply with these limits for safe exposure.

Proximity sensing for SAR

In order to meet SAR limits many designers implement circuitry to reduce the power output of a device’s radio frequency circuits when the device is in close proximity or in contact with the user. This application note from ATMEL describes a capacitive proximity circuit which can be used to detect when a device is in contact or close proximity with the user.

Arduino-controlled plant watering system

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Here is another automatic plant watering system using Arduino. The system continuously senses the moisture condition of soil and activates the water pumping system if the soil condition is too dried. The system also implements a real time clock for timekeeping, LEDs to indicate various soil conditions, and a LCD display to show various parameters including the time and the status of the water pump.

Plant watering system

Build an electric guitar tuner using Arduino

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Check this latest instructable on making an Arduino guitar tuner. The audio signal from an electric guitar is amplified and fed to an ADC channel of Arduino, which further processes the signal to extract the major frequency component in the audio. Based on the detected frequency, an LED lights up to show the note of the audio. Besides, it also indicates whether the string being played is sharp, flat, or in tune.

Arduino guitar tuner

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