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
Click here to download the full size of the above Circuit.

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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