ir volume control

Posted on Feb 4, 2014

The screen that we watch TV on at home has build-in speakers, but, because it`s actually a computer display, hasn`t got an infrared receiver. This made it impossible to set the volume with the TV receiver remote. I recently bought some Stellaris LaunchPad development boards and figured this was the perfect opportunity to make something useful with

ir volume control
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one. The idea is to receive and decode IR signals with a microcontroller and increase or decrease the volume with a digital volume control when the correct command is received. The inputs to the volume control come from the headphone out of the TV, the outputs go to a pair of active speakers. I decided to build my circuit around a development board I recently bought from Texas Instruments for a discount price of ‚¬4. 20. It`s a Stellaris LaunchPad, which sports an ARM Cortex-M4F (TI LM4F120H5QR) that can run at up to 80 MHz. There`s a build-in USB debug interface on the board, and in- and outputs are provided on two 2G—10 headers. In high school, I designed a few audio circuits and I had some TI PGA2310 chips lying around from back then. These are high quality 8-bit digital audio volume controllers with zero crossing detection. This means that they switch the volume when the audio signal is at 0V, so that there`s no audible pop from the speakers. For the infrared receiver, I used a Vishay TSOP38238, which has a built-in filter for reception of 38 kHz signals, the frequency at which most TV remotes work. I wanted to use a cheap 5V power brick to power this circuit, and the PGA2310 requires at least 4. 5V as its positive supply, so splitting the 5V into ±2. 5V was out of the question. Instead, a charge pump, the TI LM2662, is used to generate -5V. This IC requires just two external capacitors in order to invert its positive...

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