In an effort listen to his music on shuffle without the need to touch the volume knob [Mike] build his own automatic volume leveling hardware. He knows what you’re thinking right now: there’s software to do that for you. But building the feature in hardware is a great stepping off point for a project.

He started the prototype using LabVIEW along with a Mobile Studio development board and a Bus Pirate. This project will be a mix of digital and analog components and it’s a bit easier starting off the exploration with these tools rather than jumping right into the AVR code.

The circuit will sample the incoming audio, modify it accordingly, and output the result. The output side is where the Bus Pirate really shines. He’s using some MCP42010 digital potentiometer chips to make the necessary changes to the levels. They communicate via SPI and it’s nice to have the Bus Pirate’s terminal to issue commands without the need to reflash a microcontroller.

[Mike] made a video showing an audio waveform with and without the hardware leveling. Sound quality is still great, and each clip is played at a reasonably comfortable listening level. We’ve embedded that demonstration after the break.

[yotuube=http://www.youtube.com/watch?v=YaEc6_wQ9FM&w=470]

A few years back [Evan] built a kegerator from a mini fridge and was quite happy with his new beer chiller. Like many of us do, he started thinking up ways in which he could improve the project as soon as it was completed. While it took a couple of years, he recently got around to adding the temperature and capacity gauges he always wanted.

He added a temperature probe to the refrigerator, and then constructed a pair of tools that he could use to measure how much beer was left in the keg. The volume monitors include a scale built using a pair of pressure sensors from SparkFun, and a flow sensor installed in the beer line.

[Evan] scored an old Chevy gauge cluster and cleaned it up before installing a pair of analog meters which he used to show the keg’s temperature and “fuel” level. Since he feels no project is complete without some LED love, he added a few of them to the display without hesitation. The LEDs calmly pulsate when the keg sits idle, but spring to life and begin flashing when the flow sensor is activated.

As evidenced by this pair of keg monitoring systems, we think that you can never have enough information when it comes to your beer stash, so we really like how this project came together.

Be sure to check out his kegerator’s gauge cluster in the video below.

There are cars that increase the radio volume as you drive faster, and video games that ramp up the music as your gameplay improves (we’re looking at you SSX Tricky). Now you can add that feature to your workout with [Polymithic's] Motion Feedback MP3 Player. It uses a passive infrared sensor to detect motion so there’s no need to wear any electronics. But if you used some Bluetooth headphones you could bring the system with you to the gym, just don’t exercise so hard that you blow your eardrums out.

[via Hacked Gadgets]

[Jean-Michel] tipped us off about his beer keg monitoring setup. It can tell you how much beer is left in each keg, how much carbon dioxide remains in the canister, and it can monitor and regulate temperature.

An Arduino mega is the brain of the system. A shield was built to interface force sensors, measuring the weight of the keg to estimate how much beer remains. Analog temperature sensors allow for temperature monitoring and control of the compressor for regulation. Information can be displayed on a graphic LCD or a computer via XBee wireless communications.

This is along the lines of the SparkFun kegerator but we like the added functionality. Does this need to Twitter? Probably not but if you want that, it’s only a bit of a software hack away.

Dallas/Maxim’s DS1801 is an audio volume potentiometer with a simple SPI interface. This chip has two channels of volume control that might be useful in a DIY audio project. We previously looked at the DS1807, a similar part with an I2C interface. This week we’ll show you how to use the SPI version.

DS1801 SPI digital audio volume potentiometer (Digikey search, Octopart search, $6.50). Datasheet (PDF).

We connected the DS1801 to our Bus Pirate universal serial interface tool as shown in the table. We used the Bus Pirate to demonstrate this chip, but the same basic procedures apply to any microcontroller. The DS1801 power requirements are flexible, it works at either 3.3volts or 5volts, we used a 3.3volt supply.

The DS1801 has an SPI interface. The data output pin can be used to cascade multiple DS1801s. We used the Bus Pirate’s SPI mode with default options to interface this chip.

The DS1801 SPI protocol is described in figure (a) on page 4 of the datasheet (shown above). Note that the SPI enable signal, called RST on the DS1801, is actually opposite standard notation. Data input is active when RST is high, and inactive when it’s low.

Each DS1801 has two audio potentiometers with 64 steps of volume control. 0 is full volume, 63 is the lowest volume, position 64 is mute. Setting the volume is really simple; just raise the RST signal, clock in the volume level for each potentiometer, and lower RST to enact the new settings.

SPI>A 64 64 a
AUX HIGH <–RST pin high
WRITE: 0×40 <–mute setting channel 0
WRITE: 0×40 <–mute setting channel 1
AUX LOW <–RST pin low
SPI>

Here, we set both potentiometers to mute (64). First, raise the RST pin to 3.3volts (capital ‘A’, silly CSS). Next, write the mute setting for each (64 64). Finally, lower the RST pin to enact the new settings (small ‘a’).

SPI>A 0 0 a
AUX HIGH
WRITE: 0×00
WRITE: 0×00
AUX LOW
SPI>

Now we change both potentiometers to full volume by writing a 0 to each. The sets a resistance level of 0, or 100% of the input volume.

SPI>A 0 64 a
AUX HIGH
WRITE: 0×00
WRITE: 0×40
AUX LOW
SPI>

Finally, we set a different volume levels on each potentiometer. Pot 0 is at full volume (0), pot 1 is muted (64).

Like this post? Check out the parts posts you may have missed. Want to request a part post? Please leave your suggestions in the comments.

The DS1807 contains two logarithmic digital potentiometers (pots) for audio volume adjustment. Each pot has 64 volume levels plus a mute setting. The volume level of each pot is set over a two-wire I2C serial interface. We’ll show you how to connect and interface the DS1807 below.

DS1807 I2C audio volume potentiometer (Digikey #DS1807+-ND, $3.04)

Connections

We connected the DS1807 to the Bus Pirate universal serial interface tool as shown in the table, the same basic principals apply to any custom configuration. We used the Bus Pirate’s 5volt power supply, but the DS1807 will also work at 3.3volts. I2C requires a pull-up resistor on each signal line, we used the Bus Pirate’s on-board resistors connected to the on-board 5volt power supply.

Connect the DS1807 to an audio source as shown on page 3 of the datasheet. Connect the raw audio signal to the H pin and connect the L pin to ground, the attenuated audio signal will come from the W pin.

Interfacing

First, setup the Bus Pirate for I2C mode, and activate the 5volt power supply. We covered this procedure in our last parts post.

I2C>v<–voltage monitor
9xx VOLTAGE MONITOR: 5V: 4.9 | 3.3V: 0.0 | VPULLUP: 5.0 |
I2C>

With the power supply configured, check the voltage monitor (v) to be sure the 5volt supply is active and that 5volts is present at the pull-up resistors.

I2C>(0)<–list available macros
0.Macro menu
1.7bit address search
I2C>(1)<–run address search
xxx Searching 7bit I2C address space.
Found devices at:
0×50 0×51 0×52<–potential addresses
I2C>

The Bus Pirate’s address search macro is a quick way to locate I2C devices without looking at the datasheet. 0×50 is an I2C write address because the last bit is 0, 0×51 is read address (last bit 1). 0×52 is probably a group/global write address because it doesn’t have a corresponding read address.

We could also determine the address from the datasheet: the base address is 0101 plus the three address select bits (A0-2, all grounded, 000) and the write or read bit (0 or 1) gives 0b01010000 (0×50).

I2C>[0x51 r r]<–read pot values
210 I2C START CONDITION
220 I2C WRITE: 0×51 GOT ACK: YES <–device read address
230 I2C READ: 0x3F<–pot0
230 I2C READ: 0x3F<–pot1
240 I2C STOP CONDITION
I2C>

First, we read the potentiometer values at startup. [ issues the I2C start condition, 0x51 is the device read address, "r r" reads two bytes, and ] issues the I2C stop command. The default startup value is 63 (0x3f), one position above mute (datasheet page 2).

I2C>[0x50 0b10101001 0]<–write pot0
210 I2C START CONDITION
220 I2C WRITE: 0×50 GOT ACK: YES<–DS1807 write address
220 I2C WRITE: 0xA9 GOT ACK: YES<–pot0 write command
220 I2C WRITE: 0×00 GOT ACK: YES<–volume to set
240 I2C STOP CONDITION
I2C>[0x50 0b10101010 64]<–write pot1
210 I2C START CONDITION
220 I2C WRITE: 0×50 GOT ACK: YES<–DS1807 write address
220 I2C WRITE: 0xAA GOT ACK: YES<–pot1 write command
220 I2C WRITE: 0×40 GOT ACK: YES<–volume to set
240 I2C STOP CONDITION
I2C>[0x51 r r]<–read values back to verify
210 I2C START CONDITION
220 I2C WRITE: 0×51 GOT ACK: YES<–DS1807 read address
230 I2C READ: 0×00<–pot0 value
230 I2C READ: 0×40<–pot1 value
240 I2C STOP CONDITION
I2C>

Next, we update each volume pot with a separate command. 0×50 is the DS1807 write address, 0b10101001 (0xA9) is the command to update pot0, and 0 sets the volume to full. The next sequence uses the update pot1 command, 0b10101010 (0xaa), and sets the volume to mute (64, 0×40). Finally, we use the read procedure to verify that the values are correct.

I2C>[0x50 0xA9 64 0]<–write both pot values
210 I2C START CONDITION
220 I2C WRITE: 0×50 GOT ACK: YES
220 I2C WRITE: 0xA9 GOT ACK: YES<–update pot0 command
220 I2C WRITE: 0×40 GOT ACK: YES<–pot0 value
220 I2C WRITE: 0×00 GOT ACK: YES<–pot1 value
240 I2C STOP CONDITION
I2C>[0x51 r r]<–read back values
210 I2C START CONDITION
220 I2C WRITE: 0×51 GOT ACK: YES
230 I2C READ: 0×40<–pot0 value
230 I2C READ: 0×00<–pot1 value
240 I2C STOP CONDITION
I2C>

The pot 0 write command can also be used to set both potentiometer values with a single command. Use the pot0 update command (0b10101001, 0xA9), and  send the pot1 value (0) following the pot0 value (64).

I2C>[0x50 0b10101111 0x20]<–update both pots with the same value
210 I2C START CONDITION
220 I2C WRITE: 0×50 GOT ACK: YES
220 I2C WRITE: 0xAF GOT ACK: YES<–dual update command
220 I2C WRITE: 0×20 GOT ACK: YES<–value to set
240 I2C STOP CONDITION
I2C>[0x51 r r]<–read back values
210 I2C START CONDITION
220 I2C WRITE: 0×51 GOT ACK: YES
230 I2C READ: 0×20<–pot0 value
230 I2C READ: 0×20<–pot1 value
240 I2C STOP CONDITION
I2C>

Finally, 0xAF (0b10101111) can be used to update both potentiometers with the same value. This is probably the most useful command for stereo audio volume control where both channels have the same value and change simultaneously.

Are there any chips or components you’d like us to cover in future parts posts?

[jefffolly] published some straight forward plans for a passive volume control. It uses a resistive ladder built across the contacts of 12W rotary switches. Each resistor provides a 5dB difference, and he recommends using 0.1% tolerance resistors to maintain accuracy. The use of discrete resistors instead of volume pots means that the output is much more predictable. All of the RCA sockets were connected using oxygen-free copper wire.