Well I've finally got it all together and have found time between family events today to post. I have great admiration for you guys who were able to get your projects turned in earlier.
My entry is a tremolo called the" Pulsinator". I was originally going to call it the "Treminator", but an online search revealed that someone else was already marketing a tremolo under that name. I wanted to use a 555 timer for the LFO as a challenge, and boy was it!
I had run across Dead Astronaut's (Rob Henry) Tiny Tremolo which feeds the guitar signal through an LDR which is controlled by an LED connected to the output of the 555. To be different, I placed a Tillman preamp in front of the LDR to keep the signal's quality in tact (or even make it better). The biggest problem with the 555 is the ticking noise that permeates most audio circuits that share the same power supply. The Tiny Tremolo avoids this problem by having a separate ground for the LFO and the LDR since the LDR is passive. The Pulsinator on the other hand has an active amplification circuit and shares the ground with the LFO. I was able to knock almost all of the ticking using a suggestion that Jon Patton had given to another forumite. Thanks Jon! (BTW, that "Big Bertha 4700uF cap shown in the photos did the trick!
). I also found Small Bear's "Tremulous Bear", which is a nice 555 based tremolo that uses active components to isolate the ticking. Steve's configuration of the 555 gave me much more control over timing than I would have had otherwise had, so thank you, Steve!
The next problem I ran into was a popping sound unrelated to ticking from the power rails. This only occurred when there was a signal going through the Pulsinator. I was able to reduce this quite a bit by using an external pot to control the intensity of the LED in the optocoupler.
I did an extensive amount of research trying to finding a passive filter to smooth out the 555's square wave. I finally settled on a diode/capacitor arrangement that did a pretty good job without greatly affecting the volume or overall sound. I made the filter switchable between four levels of smoothing.
Once I got past the hurdles above, I had stupid irritating problems. This was the first time that I had designed a PCB. It took me a little while to realize that I didn't need to reverse the PCB image before doing the photo transfer, just the text on the board.
I downloaded the base artwork for the enclosure from a clipart site and then edited it using several drawing programs. The biggest problem with the art was getting the photo overlay on the enclosure without blemishes or uneven cuts. I finally got it and did a varnish clear coat.
On to the videos. I shot several segments of video using my iPhone. They looked good when I viewed them on the iPhone, but when I transferred them to the computer, they were upside down. So I had to spend more time finding a way to flip the video. BTW, being tired when I shot the video didn't help my mediocre playing abilities.
Here are the build documents. I apologize that I haven't had a chance to convert these into jpeg images and post them directly, but I'll
flow edit follow up and do this. The docs have been updated for new components and trace cuts that appear in the photos further down.
https://www.dropbox.com/s/0mwqr9mbk02slnt/Pulsinator%20V1.02%20Scheme.pdfhttps://www.dropbox.com/s/brcfs18amqh787o/Pulsinator%20V1.02-Copper.pdfhttps://www.dropbox.com/s/0zsfzlz3igpeq9c/Pulsinator%20BOM.pdfHere are my photos of the outside and inside. The board is copper side up because that's the only way it would fit. The copper spring on the back of the board is soldered to a large ground plane to provide grounding of the enclosure. Not shown are two strips of foam attached to the inside of the lid to prevent the board from contacting the lid. I tinned the copper to give it a silvery "Terminator" theme look.
Here's my embarrassing video:
I want to thank the judges for conceiving this contest and running it. Your time and talent is greatly appreated! Thank you also to all the sponsors (including judges) who generously donated the terrific prizes. Of course, without Aron, not only would the contest be impossible, but there would be no data source for the wealth of information that we DIYers rely on.
Finally best wishes to all of the other contestants. This has been a lot of fun and so far you've all submitted projects of a magnitude that I can only dream of.
Edit I forgot to post an image of the component layout on the board. I'll do that ASAP.
