Here’s my latest project, it’s less than 24 hours old =)

I’ve always wanted a looper effect, like the boss loopstation, mainly because the online demos were so neat. Being a bass player, I though it would help me practice with drum loops, but it’s just not worth the money unless you’re going to use it live. I ended up playing drum samples on my PC and playing along on the bass.

more (and video) after the break

About 2 weeks ago, a friend asked me about creating a digital recording circuit, for a project (which will be posted here when completed, going to stay a secret for now). Some online searching brought us to a keychain digital recorder product. After comparing some models, we found one that had 60 seconds of recording time, and we got 2 of it off ebay. I then came up with the idea to use this little recorder as a guitar looping effect, and wondered how it will handle it.

Yesterday, we met and started to disassemble and test this unit. We hooked it up to the Arduino, powered it from the 3.3V supply, and tested the “button press emulation”. We later went to a friend for a BBQ. When I came back home, I decided to continue experimentation. I had desoldered the microphone and speaker from the unit, and soldered some more hook-up wire. I had some problems with getting the circuit to function properly, I think I had a short circuit somewhere. I went to sleep without getting it to work.

This morning, I had a day off work, and decided to continue this little project. I soldered some more wire to replace problematic alligator clips positioning, and everything worked again. I connected my guitar to where the mic was, changed the Arduino code a little, and fired it up. You can see it in action on the following video:

And here’s the simple arduino code:

int recPin = 4;
int playPin = 2;
 
void setup()
{
    //prepare pins for output
    pinMode(recPin,OUTPUT);
    digitalWrite(recPin,HIGH);
    pinMode(playPin,OUTPUT);
    digitalWrite(playPin,HIGH);
}
 
void loop()
{
    //wait and then record a 5 second loop
    delay(5000);
    digitalWrite(recPin,LOW); //"hold down" rec button
    delay(5000);
    digitalWrite(recPin,HIGH); //release it
    delay(30); // to pass debouncing
    while(1) {
        digitalWrite(playPin,LOW);
        delay(30);
        digitalWrite(playPin,HIGH);
        delay(4970);
 
        digitalWrite(playPin,LOW); //emulate a second click, this will stop playing the sample, and will be ready to play
        //again in the next loop iteration
        delay(30);
        digitalWrite(playPin,HIGH);
        delay(30);
    }
}

When I continue working on it, I will need to build some sort of preamp for the output signal. I will also recreate the Arduino program on a PIC 12F675 (or whatever the model number is) of which I have quite a few. There’s also need for better timing, and a pushbutton to start/stop loop recording (and adjust the length of the loop accordingly).

I hope to get it to a usable state, and have some creative fun with it. Now it’s time to get back to my homework in algebraic structures.

A Tremolo is an effect unit that modulates the amplitude of the guitar signal, usually in a triangular waveform. This version uses a square waveform, for a more switching, chopping kind of effect. This kind of effect can be heard in the beginning of Plant Telex by Radiohead. Tom Morello of Rage Against the Machine uses this kind of effect too, he, however, uses a “kill switch” on his guitar, which he controls manually.

More after the break…

This is a very simple and low quality circuit, whose problems can be seen in the following video. I built it in about an hour, that’s how simple it is. It is based on a simple NAND oscillator from an LED Chaser circuit that I had built maybe a year ago. Here’s the circuit diagram(proudly drawn in GIMP):

Values that I had used in my circuit:

• Supply Voltage: 5VDC
• R1 – 1MOhm
• R2 – 10KOhm
• C1 – 47uF

The idea behind the circuit is quite simple. The NAND provides a square wave pulse (and there are better places where you can understand how it works, google “NAND oscillator”) that is then hooked up to the 4066 IC. The 4066 is contains 4 analog switches, where each switch is controlled by a single input pin – as seen in the following diagram:

The 4093 NAND IC contains 4 NAND gates, so I used a free one to invert the clock signal.

I used 2 of the 4066 switches. The first one, connects the input signal + and the output signal +, while the second one connects the output signal + and the ground. One switch is controlled by the output of the oscillator, and the other is controlled by the same output, but inverted. The result is that the output signal switches between the input signal, and no signal (ground connected to +).

This is rather primitive, but that’s the whole point behind this simple project !

Here’s a short video showing my prototype and live demo of the effect (grr, I forget my entire English vocabulary when I talk):

I will be glad to hear any ideas as to how to improve the circuit. My main goals are:

• Eliminate the POP noise
• Allow higher frequencies
• Add a 4017 counter with 8 switches(representing one bar) that will allow more complex chopping

I have loads of bipolar transistors, maybe I’ll try to use them instead of the 4066…

That’s it ! Please let me know if you build it yourself !