4 Channel Audio Switcher

Overview

The purpose of this project was as a test to see if the 4051 mux would be usable in audio switching. I've been designing a programmable guitar pedal switcher and used this as a test project to see if there were any fatal issues with using them for this purpose. I also had some attiny85s around and hadn't found a project for them. Being able to use two pins to control the select lines of 3 muxes was a perfect use case.

In a future iteration I'll try the 4052 mux, the only reason I didn't use one this time is because I didn't have any, and I have heaps of 4051s lying around.


Bill of Materials

• Attiny85
• 3 x 4051 Multiplexers
• 2 x Momentary buttons
• 4 x Leds
• 5 x Stereo sockets
• 1 x 7805 Voltage regulator
• 2 x 10uF electrolytic capacitors
• 3 x 1k resistors

Code

The code for this is pretty basic, and self explanatory, with the attiny only using 2 inputs and 2 outputs. Each of the buttons either increments or decrements the current channel. Since the switcher only has 4 channels, only the first 2 select lines are used, with the third select line tied to ground. All 3 4051s use the same select lines.

Using enum classes in this context is a bit overkill, but I've been trying to use as much c++ stuff as possible recently to get more comfortable with it.

I take advantage of the fact that the leds are powered through the common line on the multiplexer to use only one current limiting resistor for all of the leds.

	/*
	4 Channel Stereo Audio Switcher
	Multiplexer pins connected to 3 separate muxes
	MUX 1 = Audio left
	MUX 2 = Audio right
	MUX 3 = Led display
	*/
	#define NUM_CHANNELS 4
	/* Mux select pin indexes */
	enum class Select
	{
	A = 0,
	B = 1
	};
	/* Button pin define indexes */
	enum class BtnInd
	{
	INCR = 0,
	DECR = 1
	};
	/* Pin defines */
	const uint8_t MUX_PINS[2] = {3, 4};
	const uint8_t BUTTON_PINS[2] = {0, 2};
	/* Channel States */
	uint8_t current_channel = 0;
	uint8_t prev_channel = 0;
	void setup()
	{
	for(uint8_t i = 0; i < 2; i++)
	{
	pinMode(MUX_PINS[i], OUTPUT);
	pinMode(BUTTON_PINS[i], INPUT);
	}
	}
	void loop()
	{
	read_buttons();
	if(prev_channel != current_channel)
	{
	channel_set();
	}
	}
	/* Increment or decrement current channel */
	void read_buttons(void)
	{
	if(digitalRead(BUTTON_PINS[(uint8_t)BtnInd::INCR]) == HIGH)
	{
	prev_channel = current_channel;
	if(current_channel < (NUM_CHANNELS - 1))
	{
	current_channel++;
	}
	delay(250); /* debounce */
	}
	if(digitalRead(BUTTON_PINS[(uint8_t)BtnInd::DECR]) == HIGH)
	{
	prev_channel = current_channel;
	if(current_channel > 0)
	{
	current_channel--;
	}
	delay(250); /* debounce */
	}
	}
	void channel_set(void)
	{
	digitalWrite(MUX_PINS[(uint8_t)SELECT::A], (current_channel & (0x1 << 0)));
	digitalWrite(MUX_PINS[(uint8_t)SELECT::B], (current_channel & (0x1 << 1)));
	}

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Schematic