Photography and illustration by Michael F. Zbyszynski

ELECTRONIC CRICKETS

Create a nighttime chorus by modifying solar yard lamps.

By Michael F. Zbyszynski

Much of my creative work as a composer and sound artist relies on multimedia computers to generate and manipulate sound. Unfortunately, this method has a limitation: I need plenty of electricity, preventing me from installing art in parks and outdoor spaces without AC power.

Rather than ignore such opportunities, I started thinking about solar power. It was David Zicarelli (of Max/MSP fame, see cycling74.com) who suggested I look at the “solar garden lamps” that are ubiquitously available in hardware and home stores.

For a maker, solar lamps represent a tremendous bargain: for $5 you can get a solar cell, batteries, charging circuitry controlled by a photoresistor, and a functional, waterproof housing. I’ve never been impressed with these in their intended function as a light source, but they are an interesting platform for more creative use.

For this project, I wanted to make something that reminded me of many beautiful phenomena of summer nights: crickets, chirping frogs, and fireflies. By day, the lamps seem ordinary; they sit and charge their batteries like all their unaltered cousins. But as the sun goes down, each one starts blinking and chirping. The sound and rate of their song are determined by the temperature, the amount of sun they receive, and the natural variance of their components. The emergent quality of dozens together can be fascinating. This project has a certain affinity to BEAM robotics (see MAKE, Volume 06, page 76).

It took some shopping to find the right lamps. I wanted to use a large number (my current installation has 20), so price was a major factor. Also, typical garden lamps come with either 1 or 2 AA batteries as a power source. Two batteries in series yields double the voltage (nominally about 2.4 volts for rechargeables), so I preferred those lamps. I found a 4-pack of lamps at my local mega home store for $20. I think stores discount these heavily on occasion, as a loss leader, so look around a bit.

Fig. A: Half of this circuit is a modified astable multivibrator, a handy circuit for blinking things. I slipped in a thermistor in place of one of the ordinary resistors, so that the timing would be temperature-dependent. The other half of the circuit is a Hartley oscillator. I tuned the component values up so that it sounded the way I liked at the relatively low voltage I was expecting.

In designing the electronics for this project, I decided early on not to use any microcontrollers. I wanted everything to be as simple and generic as possible. My goal was to make a circuit that blinked an LED every second or so, depending on the temperature, and simultaneously triggered some sound generator that I found pleasing. The final design looked like Figure A.

1. Make the circuit.

Refer to Figures A and B to build the circuit.

2. Open up the lamp and remove the LED.

Unscrew the housing to find a circuit board, also screwed in. Carefully unscrew it, leaving it connected to the solar cell and photoresistor, and use a soldering iron and desoldering pump (or braid) to remove the LED from the circuit board. Save this LED for another project. Remember the location of the LED because that’s where you’ll add the custom circuit in the next step.

Fig. B: I was given a bunch of old Veroboard by my colleague Adrian Freed (one of his many contributions to this project). Snap the board to the right size using a straightedge. Solder the parts in as per the schematic. I tried to keep it fairly compact, so it would fit inside the lamp housing. I cut off the left end of the stripboard (including the LED, which is there for testing) before installation.

3. Install the circuit.

Use short wires to connect the positive (check with a multimeter) and negative pads, where the old LED was, to the power and ground of the custom circuit.

Next, attach a new LED and speaker to your custom circuit. I ran the wires for the speaker through a hole in the bottom half of the housing, and used the speaker magnet to stick to a battery. Different speaker positions create different sounds, so feel free to experiment. Use a shorter pair of wires to attach the new LED to the custom circuit. The new LED probably will not fit perfectly into the space of the old LED, so liberally hot-glue it. The hot glue also provides insulation and weatherproofing. Do not cover the lens of the LED with glue.

4. Tune up your lamp.

Cover the photoresistor with your hand or a piece of tape, and see how it sounds (make sure the batteries are charged). Adjust the potentiometer to get a good sound, making sure that each lamp has its own tone that is different from its neighbors.

5. Close up the lamp.

Delicately bend the extra wire and the 2 circuit boards into the housing of the lamp. Go slowly, and it shouldn’t be too hard to fit everything in and screw the lamp shut.

6. Install and enjoy.

These lamps have the same needs as their standard brethren. Put them someplace that gets a fair amount of sun and is out of the way of foot traffic. The most interesting effect is when you can see and hear a number of them. They are quite visible, but fairly quiet. I have 20 lamps encircling a mediumsized yard, with about 2' between each lamp.

As the twilight begins they will each start chirping, tentatively at first. By sunset they will all be singing.

See the cricket lamp in action: makezine.com/11/diyoutdoors_cricket

Michael Ferriell Zbyszynski (mikezed.com) is a composer, sound artist, performer, and teacher in the field of contemporary electroacoustic music. He is assistant director of music composition and pedagogy at UC Berkeley’s Center for New Music and Audio Technologies.