My Preamp Project: Arduino, I2C, relay selector+attenuator, tube stage

[maxw]

Originally Posted by TheShaman

Max,
What are the impedance specs of your attenuator?
I'm considering using it along with a Salas DCB1 buffer (which is optimally paired with a 10-20k pot).

It's the same schematic/specs as the AMB Delta:
The δ1 Relay-based R-2R Stereo Attenuator
I think my current one is around 20k.

[glt]

Originally Posted by maxw

That is the example I was going to post as it neatly shows the problem with LCD screens - Yes they can look really nice BUT the front panel must be machined to fit the LCD perfectly. Having access to machining tools is a luxury I don't have. I think you need to know someone otherwise the tooling and set up costs are crazy! Cutting a nice circle using a hole saw with my drill press is about the extent of my tools

This is the kind of implementation that makes me dislike LCD screens:

DIY: AMB/linuxworks labs alpha10 audio preamp | Flickr - Photo Sharing!

Totally agree. But if you use wood and a steady hand you can get something like this:



Your implementation of a colored LED to indicate volume level is a great idea!

[washburn_it]

This is a pic (sorry for the poor quality and reflections) of the actual "user interface" of my preamp:



The preamp is still into the "prototype phase" (as you can clearly see ) but basic functions are already working.
"Selezione Ingressi" means for "Input Selection" and it is done by "clicking" with the finger on the correspondant icon.
Clicking on the volume level box activates the MUTE.
The volume is set by using a PGA2310 and an optic encoder, the balance function is made by regulating individually the volume of the desired channel.
Min and max value of the volume (shown in the "volume bar") are set in the configuration page (still in development) and the "volume bar" steps are calculated according to these values so that it reflects the actual volume level.
The volume level displayed in the box is calculated considering the total gain of the "analogic" preamp but this value will be "fine" adjusted when everything will be completed measuring the gain with an oscilloscope.

[washburn_it]

I post the pic again since the previous seems to have a problem:

[maxw]

Originally Posted by washburn_it

This is a pic (sorry for the poor quality and reflections) of the actual "user interface" of my preamp:
The preamp is still into the "prototype phase" (as you can clearly see ) but basic functions are already working.
"Selezione Ingressi" means for "Input Selection" and it is done by "clicking" with the finger on the correspondant icon.
Clicking on the volume level box activates the MUTE.
The volume is set by using a PGA2310 and an optic encoder, the balance function is made by regulating individually the volume of the desired channel.
Min and max value of the volume (shown in the "volume bar") are set in the configuration page (still in development) and the "volume bar" steps are calculated according to these values so that it reflects the actual volume level.
The volume level displayed in the box is calculated considering the total gain of the "analogic" preamp but this value will be "fine" adjusted when everything will be completed measuring the gain with an oscilloscope.

Very cool, love it. The cardboard and tape front looks good too

Did a library come with the touch screen? Or did you have to write your own?

[randytsuch]

For a temp sensor project a little while back, I made this, using a hand drill, nibble and a file.

Bought the bezel from Digikey or Mouser, uses a standard 2x16 LCD, connected to an Arduino.

It also has a bluetooth interface, so I can get info through bluetooth to a Processing program running on a laptop. I have a switch to select USB or bluetooth on the arduino.

Randy

[washburn_it]

Originally Posted by maxw

Did a library come with the touch screen? Or did you have to write your own?

Unfortunately not, I had to write everything by my own, included a font to display text messages but it's not complicated.
To manage the touch capability you need 4 ADC (analog to digital converter) to read a voltage that is proportional to the position of the screen where you touched.
It communicates with the micro through an 8 bit bus and has some control lines, the only command that you need is to send it the coordinates of the pixel that you want to turn on and the color of the pixel.
Actually to turn off a pixel you just need to send the color "0" (black).
The negative side of using color (graphic) LCD is that they need a lot of kbyte if you want to display a bitmap.
In my case to display a full 320x240 (256 colors) bitmap I would need 76800 bytes since every pixel is represented by its color that is codified with one byte or 8 bit (RRRGGGBB).

[Bonsai]

You can get a completely free high end graphics library from NXP that will run on any of it's ARM controllers. Go onto their website and look und MCU. The manual is 1000 pages long and is based on the Segga GL. The library includes full touch screen support.