http://mrbichel.com

Together with Troels Just Christoffersen I hacked together a screaming potter. The idea is to create the impression that some kind of screeching creature is living within the potter. The schematic and code are simple, a photoresistor activates the speaker when its subjected to light.

Schematic

Schematic

Arduino code

int photoResistorPin = 0;
int startThreshold = 4;
int speakerPin = 9;
int active = false;
int activationTime;

void setup() {
    Serial.begin(9600);
}

void loop() {
    int lightReading = analogRead(photoResistorPin);
    if(lightReading > startThreshold) {
        // when first activated set timestamp
        if(active == false) {
            activationTime = millis(); 
            active = true; 
        }
        // the time could be usd to create more variation in the sound 
        // int runtime = millis()-activationTime;

        for (int i = 0; i < 6; i++) {
            int frequency = lightReading*i;
            Serial.println(frequency);     
            tone(speakerPin, frequency);
            delayMicroseconds(500);
        }
    } else {  
        noTone(speakerPin);  
    }
}  

Me and my friends wanted some sound in our camp at this years Roskilde Festival so I set out to build us a boombox.

I ordered an amp6-basic kit from 41hz.com because of the many recommendations I have read and because the kit comes with mostly through hole components and is relatively easy to solder.

After soldering i mounted the amp in an aluminum plate from an recycled aluminum profile. It was quite a revelation to discover how forgiving aluminum is as a material. I have added a 50k Ohm stereo log pot for volume control a stereo minijack input and a switch that i wired to the 12V input since it didn’t seem to produce any noticeably larger turn on thumbs than the sleep jumper. I somehow managed to reverse the volume pot, meaning you turn it up rotating against the clock, and the power level seems to max out when turned half way around. It is not important for this amp, but for the next one I will look into improving the volume control, perhaps using an attenuator and an active preamplifier – can anyone point me to a good DIY volume control or preamplifier guide/advice? Currently the amp is powered by a screw machine battery but we are planning to bring a car battery to power it during the upcoming festival.

The amp sounds great, and is loud enough even through 8 Ohm, and being a class T amp it is very efficient thus giving us many hours of music on a recharge.

Next up is encasing the amp and speakers providing it with weather protection and fitting it with wheels, i am hoping to find some large bicycle wheels. Right now i am considering a light design using two 8 Ohm compact speakers, or using 2 heavier 4 Ohm speakers, they are very old and rated to 15W RMS which is not quite as much as the 25W RMS the amp outputs through 4 Ohm, I am not sure if this will be a problem.

On a side-note fooling around with electronics for the past 6 months i have been wondering why we are not all running with 12V DC as mains. I suspect there are a few reasonable arguments but i haven’t been able to find them.