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Circuit Notebook

Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates.

Kill those adverts quickly with the Supermute

Click for larger image

The Supermute is a TV remote that turns the TV on or off, mutes the sound and varies the volume up or down, using only three buttons. The mute/on/off button is an industrial emergency stop button which makes it easy to kill pesky adverts.

The circuit comprises a Microchip PIC12F675 8-pin microcontroller, FET Q1, infrared LED1, the emergency stop button and two small pushbutton switches for the volume control. Holding the emergency stop button down for a second or more alternatively turns the television on or off.

A quick slap of the emergency stop button with an open hand (or closed fist!) or a prod with the foot mutes or un-mutes the TV. The pushbutton switches raise or lower the volume.

It is set for a Sony TV which has a simple IR protocol – a 5-bit address to identify the device being controlled (TV, DVD player, VCR, etc) and 7-bit commands. The carrier frequency is 40kHz. The PIC program uses the SLEEP function to limit the off-state current to less than 1mA and is woken from SLEEP with any change on input ports 1, 2 or 3.

You can determine the bit pattern by a web search or by measurement with the device’s original remote, an IR detector on a breadboard and an oscilloscope.

The emergency stop button is an industrial Allen Bradley unit. Jaycar have a cheap latching button emergency stop (Jaycar SP-0786) that can be converted easily to non-latching but it is not as robust. Jaycar also have a number of large momentary contact pushbutton switches.

The software can be downloaded from the SILICON CHIP website.

Andrew Buchanan,
Tawa, NZ. ($50)

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