WM8816-LM4562 Board Design

[Gcollier]

After taking a look at the new LM4562 from National I was mighty impressed by it's specs. I decided to design a board around it using the WM8816 from Wolfson to control the gain. I figure this is the next best thing to a stepped attenuator, but this also has the advantage of having a fixed input impedance.

The design itself is pretty basic. A PIC16F88 (love this chip) will be used to control the WM8816, which sets the gain of the LM4562. I have added headers for ICSP, auxiliary control of the WM8816, and the individual PIC ports for the connection of buttons, an IR Reciever, or an LCD etc. I still need to program the software for the PIC, so I will be working on that for the next little while.

What I am most interested in right now are some ways I can improve the design. If you have any constructive suggestions please fire away.

G.

[Gcollier]

Here is the board.

[Gcollier]

A 3D View of the Board

[Carl_Huff]

I've been looking to grow my PIC programming skills. The 16F88 looks like a great place to start. Can you recommend a good 'C' compiler and development system?

[Gcollier]

Originally posted by Carl_Huff
I've been looking to grow my PIC programming skills. The 16F88 looks like a great place to start. Can you recommend a good 'C' compiler and development system?

Actually, I don't use C myself. I have been using Picbasic and Mikrobasic. You could take a look at this product http://www.mikroe.com/en/compilers/mikroc/pic/ if you are set on using C.

The PIC16F88 is indeed a very nice chip. It has nearly every feature you could ask for (well except USB...) and is in a nice sized package. The internal oscillator is a nice feature and also frees up two more pins for I/O options. I am by no means an expert at PIC programming, but I am competent enough to handle simple things like SPI. For programming my PIC I built this unit http://feng3.cool.ne.jp/en/pg5v2.html which I use with WinPIC. I also have a little JDM programmer with an ICSP header on it, you can find the details for that one here http://www.belza.cz/digital/jdm.htm.

G.

[Russ White]

Man that is some good stuff mate.

Good work, and thanks for sharing!

I have a very very similar circuit for the same Wolfson chip, but with the PIC16F690(or its brothers) and AD8610.

I currently experimenting with the 8816 in a pretty unconventional way... (think symmetry)

BTW the LM4562 is just plain awesome. I just can't believe how good it is for the price it will be sold at.

Cheers!
Russ

[Gcollier]

Originally posted by Russ White
Man that is some good stuff mate.

Good work, and thanks for sharing!

I have a very very similar circuit for the same Wolfson chip, but with the PIC16F690(or its brothers) and AD8610.

Cheers!
Russ

Russ,

Thanks for the comments! You have me curious now! What are you doing with the 8816. Are you using it with a balanced circuit like the THS4130?

I may still make some minor changes to the PCB. I already added a 220nF decoupling cap for the digital supply on the WM8816. I may also change the hee supply and have a seperate one for the WM8816 and the opamp. I can likely do this with some additional jumpers.

G.

[Russ White]

Originally posted by Gcollier


Russ,

Thanks for the comments! You have me curious now! What are you doing with the 8816. Are you using it with a balanced circuit like the THS4130?

G.

Oh your welcome, I am happy to say you have been one I have learned a lot from around here. So thanks right back at ya!

Well yes, but not in a way you might expect. The THS4131 is CFB which I am sure you realize complicates things a bit. I don't use it conventionally with the 8816, but... in the global feedback of a super symmetrical power amp for a integrated amp (TXO). It does work(and very well), however I am torn between this chip and a more "discrete" approach. So far I would have no qualms using the wolfson chip.

Cheers!
Russ

[jaycee]

Sorry to butt in with an unrelated question, but what's the program that you used to generate the 3D view from the EAGLE board?

[Gcollier]

Originally posted by jaycee
Sorry to butt in with an unrelated question, but what's the program that you used to generate the 3D view from the EAGLE board?

No problem, I used the Eagle3D ULP available here http://www.matwei.de/

Eagle3D generates a .POV that you can use with POVRay, a freeware raytrace program, to generate the images. The ULP is not entirely user friendly unless you stick to very specific libraries, but once you get the hang of it it is pretty easy. Also there is a tutorial here http://felixchenier.homelinux.com/Ea...ttutorial.html that shows you how to make you own parts.

On another note, I need to change the input cap, or remove it completely. It seems that the low end rolloff created by the RC filter on the input of the WM8816 is way to high (~48Hz). I think that I will just remove it entirely. This should also allow me to get another decoupling cap closer to the analog supply pin of the WM8816.

G.