Conception of a lcd volume display for dummy

[skappy]

Hi Everybody,
that's quite a long time now that i'm thinking about making a digitally controlled volume module for my gainclone.
I would like to use a digital pot such as DS1802 or 1669 AND i also would like to display a kind of volume counter on the LCD (pressing + touch increase +1 of the displayed counter). I have well understand that a µC will be needed

Do you know where i can find assistance or even a model or a schema of such an item ?

Thank you very much for your help

[Russ White]

The PGA2311 is an excellent choice, with better specs and performance than the DS1802.

Here is one design which utilizes it:
Digitally controlled preamp/headphone amp

Cheers!
Russ

[skappy]

Hi,
i'm very sorry to disturb you once again but i need your assiatnce in the electronic field...

I'm a fond of electronic but i'm a beginner too and i would like to install a numerical potentiometer and a lcd display on my gainclone amp.
My biggest problem comes from the fact that the ampli consists in 3 gainclones kit operating together in order to obtain 6.1 amplification.

1) Do you know how i could manage the general (=3 amplis) volume level simultaneously ?

2) How can i display the value on a lcd ?

3) is it possible to store this value when the ampli is switch off ?

4) Do you know if i can find such an item as an electronic kit ?

i would like to be able to manage this project on my own but my level is too poor for that ...


Thank you very much for your help and your patience ...
Good Luck in your project

[I_Forgot]

The PGA2310, and some National Semi LM series attenuator chips use "3-wire" signaling to control the level setting. Each chip controls the level of 2 channels, unless you want to use them for a single, balanced channel.

3-wire signaling is very easy to implement as "bit-banging" using a microcontroller. Some of the chips are addressable individually, some not. If you use individually addressable chips you can implement balance controls in software.

So, you need a microcontroller and as many attenuator/volume chips as required for the number of channels you want to use. You also need some user input to the microcontroller. That can be a few pushbutton switches, a remote control (RF or IR), or a rotary encoder (optical or mechanical), or a pot if the uC has an a/D converter.

If you must use a display (is it really needed for a volume control?) the common, cheap LCD display modules usually have their own controller with a 4 or 8 wire interface, are also easy to talk to using the uC that is controlling the attenuator/volume chips. Most of those LCD displays have very small character heights, so will not be readable across a room if you're doing remote volume adjustment. You could make your own, large display using large digital clock display LEDs, or even discrete LEDs, but then you'll have to write more code to control them directly from the uC that is controlling volume.

How do you get started with all this? Read, study, learn, play with a uC. I suggest PIC microcontrollers for low cost, ready availability, and huge community of people who have been using them for a long time and can help you if you have a problem. You need a programmer, to physically "burn" your code into a uC, a suitable uC chip (it doesn't take much memory to implement a volume control 1kB -4kB is probably enough unless you get really fancy with your circuit). A prototyping board is nice to have to test pieces of code, or you can just do the development on your volume control board (not recommended for beginners). You will need a development software package in the language of your choice. Assembly language (free from Microchip) gives you the most control, C costs money but allows you to work at a little higher level. There are a ton of web sites with DIY burners, DIY prototyping boards, basic programming info, and etc., and don't miss the huge number of app notes on Microchip's web site, many with pieces of code you'll be able to just lift and use. There are also a few good books on using PICs (Easy Picin', etc.) available.

If you're going to use an LCD display, make sure you get a data sheet for the thing that shows the control signal timing. You will need to know it in order to make your uC drive the thing correctly. Same goes for the volume/attenuation chips.

I_F

[skappy]

Hi,
thank you very much for your help, i will follow the mentionned steps , but the way will be long as i have never work with µC.
I have 2 more questions :

1° What do you think of basic PIC ?
2° what kind of µC would you choose for this project ?

Thank you very much for your help

[I_Forgot]

You can probably get it all to fit in a 16F84 (is that a current part no?). These chips are so cheap you may as well get one with more memory so you'll have all the room you'll ever need. 4kB or 8kB should enable you to read an IR remote control, rotary encoder, implement balance control, maybe some input switching, some AC power switching, LCD display update, and etc. You may want more I/O pins too, unless you want to make it a really simple device. Any way, there isn't more than a $5 price difference between a 1kB part with 15 I/O lines and an 8kB device with 23 I/O lines, so get the bigger part. You could go the other way and keep the whole thing really simple and probably make it work with an 8 pin IC.

I built a dual attenuator using PIC16F84 and a NS attenuator chip. It used up and down buttons to control the volume, and one button for mute/unmute. It took 112 bytes of assembly code to read the buttons, turn on/off the mute LED, implement ramped mute/unmute, and bit-bang the attenuator chip via a 3-wire bus. I put the uC into sleep mode when it wasn't actually changing the volume so the clock would stop and there would be no possibility of digital noise getting into the audio. The attenuator chip stepped in 0.5 dB steps and there was absolutely no popping or clicking as the volume changed.

As I recall, the NS chip had a weird pinout that made doing a good low noise PCB layout difficult. I think the PGA2310/11 has a better pin out that allows you to separate the digital and analog grounds.
If the only digital stuff is the controller, and you put it to sleep when it isn't actually changing volume, the grounding scheme doesn't really matter.

I have seen the chips with a basic interpreter, but never used one. Assembly language is a little harder to learn but much more powerful. If you're only going to do one project and don't want to get into the details of assembly, the basic interpreter is probably a good idea.

I_F

[skappy]

Thank you very much ,
I think that i will start with Basic just because it seems to be easier than Assembler. I will keep the assembler for later (muy last experience with assembler was with a Commodore 128 ...)

Have a nice day

[josiphal]

Skappy, DS1802 is just fine for this, if you don't need display. It works without uC. Look here.
Else, for display and other pots, find some uC.

Josip