Sunday, March 31, 2013

Simple MFOS LFO & Acid Etched Front panel

After all the trouble I was having with the 8038 Chips, I decided to build a new LFO module based on a different design.  Early on, I tried building the MFOS super simple dual LFO but I couldn't get it to work.  I decided to try it again, now that I'm better with electronics and it worked fine.  In retrospect, the mistake I made the first time-was most likely my interpretation of the schematic. Notice the inverting and non-inverting inputs on IC1-D and IC1-A are flipped, so if you are not looking carefully, you may wire them incorrectly.

I always breadboard my projects first and especially when they might need to be modified because they supply voltages are different.  This schematic worked well but I changed a few of the values based on what kind of components I had around.  I changed out R7 with a 20k resistor to bring the square wave output up to +/-10v, so I can use it as a clock signal.  I changed R90 to a 2k4 resistor because I didn't have any 3k resistors.  I also changed out R8 with 1K resistor because when the frequency knob was at it's farthest left point, the wave would stall out, I don't know if this had something to do with using +/-15v vs +/-12v.

I made my own PCB for it, but I'm not going to share it because the one on MFOS works perfectly well.  I only did mine because I like the challenge of creating PCB layouts and I wanted to use a 1m and 2m resistor in series instead of a 3m because I didn't have any around.  I also wanted the LEDS to be connected to the triangle wave because I think it looks cooler to have LED's fade on and off instead of just be on or off.

There was another thing I really wanted to try with this project.  I've been acid etching PCBs for a while now, and it seems like a cool idea to acid etch a front panel too.  If you're only creating one or 2 modules, the idea of going through the whole process of creating a silk screen seems like a waste of time and money.  I made the layout in photoshop just like I do my PCBs.  I did a nice halftone of Sigourney Weaver from Alien.
I used steel wool on the aluminum panel before I did the transfer.  The transfer process was extremely painstaking,  I had to go back with the iron several times and reapply the transfer.  I also burned my fingers trying to pick up the panel in order to hold it against my window (a method I use to rapidly cool it off). 

I put it in a nice big tub and went all willy nilly with Ferric Chloride.  One thing I learned was that Ferric Chloride works a hell of a lot faster on aluminum than copper.  It kinda freaked me out the way it starting fizzing and spewing out(probably poisonous)gas.  The container got really hot too.  I found that if I ran around my yard with it, shaking the tub back and forth, it kept the bubbling down-and it seemed like it might not explode into flames. After about a minute, or at least I assume,  I dumped the whole thing out in my yard and sprayed it off with hose. 
I was almost positive that it didn't work, but after I washed it off and rubbed it with steel wool again, I realized,  IT LOOKED AWESOME!!!

I think next time,  I will thin out the acid with a little water and leave it in the acid for a shorter amount of time, like 45 seconds or something.  Down near the bottom, it over etched a little, but it still turned out really cool.  

I drilled all the holes and put the parts on and it looks great! 

Here's some photos of me assembling my PCB too

Those two circled points are mistakes I made in my PCB design.  Luckily I noticed them early on and it didn't take much to fix them. 

I use angled aluminum for my mounting bracket.  I had to cut and file this one down a bit in order to make it fit between my components.  

Here's a video.  It's the module on the top right. 


  1. Hey Charlie,

    This is really impressive. What do you use to get the etch resist transfer onto the Aluminium panels? Is this something generally available? I'd like to try this.


    1. I used that press and peel blue stuff for the transfer. You need to use a laser printer to print on it. the hardest part of the whole process is getting a good transfer. make sure the aluminum is clean and the iron isn't too hot or not hot enough. I found with later etchings, that using a watered down version of ferric chloride allowed for a less reactive etch. if you get the ferric chloride from radio shack, you're gonna wanna do a 1 part water to 1 part ferric chloride. I suggest you do this outside and with a respirator, I am not a chemist and I don't know if the gas it makes is harmful. cover everything you don't want to etch with paint or tape. leave it in there for about 5-8 minutes. agitate the solution.

  2. Just to let anyone know, there is a less toxic etchant available: copper sulphate. (Actually, it's not an acid etch process, more like some electrochemical thing... so technically it's not etching). It's sold in various names such as Root Kill. It's used for roots that have invaded plumbing. Printmakers use this and sometimes call it a bordeaux etch. I've only etched zinc with this but it works on aluminum too. Just make sure you buy one that is made of unadulterated copper sulphate. Use a few tablespoons per litre or water and test first!

    1. yeah, in my later projects and blog posts, I used copper sulphate.

    2. Are you using 1:1 copper sulfate and table salt? Maybe you've described it in your blog already... I'll check. Btw, thanks for all your descriptions, been a great resource for me as I trundle my way through SDiy.

    3. OK, yup, found the more recent post re salt/copper sulphate. Feel free to delete that last post, I can't seem to edit it out.

    4. I actually etched this with ferric chloride which I'd already used a bunch of times to etch copper, but later down the line, I do use salt and copper sulfate.