How it Works: Direct Drive Circuits

By Alex Nathanson updated on 4/30/2019

For a brief introduction to some of the terms used in this article, check out the glossary section.

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The simplest circuit you can make with a solar cell (also called a photovoltaic cell) is a direct drive circuit. This circuit is just some solar cells wired in series with a load, without a battery. In this tutorial I’ll be describing the circuit and reverse engineering Joe Jones’ direct drive sound making instruments to show you how to create your own.

Direct drive refers to the unfiltered immediacy of the power source. At its most basic level the solar module is wired directly to the load, without any batteries, supercapacitors, or other power regulating circuitry in between. With these types of projects there is a 1 to 1 connection between the power the photovoltaic cells are generating and the output of the circuit. The circuit doesn’t store any energy, so when a cloud or your hand passes over the device the voltage drops and it’s output decreases immediately.

While the circuit is simple, with a little creativity you can make a wide range of dynamic projects with these basic ingredients. The aesthetic output of these types of projects is as much dependent on the physical arrangement of the components as it is on the electrical specs. For example, if you place solar cells on only one side of an object it will only run when light hits that particular side, but if you place solar cells facing multiple directions it will operate in a wider range of light conditions. Neither is necessarily better or worse, it just depends on the context of the work and your intentions for the project.

As you experiment with this circuit, it’s important to remember that solar power is extremely environmentally dependant. If you’re building something that you want to use outside in an unpredictable environment, not just under a lamp indoors, you’ll need to take it outside to fully understand how your project will function in real world conditions.

This illustration describes the behaviour of a basic direct drive circuit.

1) It works when enough light hits the solar panel. 2) It stops working when an object passes over the panel. 3) It doesn’t work at night or without artificial light, because it does not store any energy.

Joe Jones (1934 - 1993) is a Fluxus artist whose instruments rely on elements of chance to create interesting musical compositions. Almost all of his solar powered instruments implemented relatively simple direct drive circuits. He would connect small solar panels to DC motors that would spin objects which would hit stringed or percussion instruments.

Jones’ first solar powered instruments were built in 1977. He began conceiving of them in 1964, but had to wait until solar panels became more affordable to be able to construct his projects. In a 1975 illustration titled Out-door Piece he described his plan for a performance using solar energy that would include elements of chance and would sound interesting throughout the day.

Many zitar, wind chimes, and drums, etc. are hung from trees at random distances at different positions from the sun so that at a certain time of day one or more will be playing as long as the sun shines becoming a sound forest.

There are five elements that determine how Jones’ instruments and installations sound; solar module choice, motor choice, sound making elements, installation techniques, and environment.

1) The type, amount, and configuration of solar cells determines how much power they produce. More or larger cells require less sunlight to turn the motor, while smaller cells may only work in the brightest light around noon. Bigger is not necessarily better. If your panel outputs too much power the sound your instrument produces may stop being interesting and just be loud or it may spin too fast and tear itself apart.

2) The motor choice impacts the speed at which it spins. The motor’s power rating (its voltage and amperage) determines how much power is needed from the solar panel. Motors usually specify a range of operating voltages and amperages and as long as your solar panel specs are close to that range you should be fine. Because your solar panel output varies with the light conditions and the motor runs slower or faster at different voltages there’s frequently some amount of guesswork and experimentation needed to until you find something that works and sounds good.

3) The percussive elements determine the characteristics of the sound. In most of Jones’ work he attached either a wire or a ball on a string to the motor and placed a percussion or stringed instrument nearby so that when the would motor spin it hit those objects. He would typically use traditional instruments, like drums, chimes, ukuleles, or zitars. Try experimenting with different objects, like paper, stretched out rubber bands, pots and pans, etc.

4) The physical position of all of these elements in relation to each other and the light source is another crucial factor in determining how these instruments function. The method you employ to physically connect all of your components and install them in a space will impact the sound as well. Hanging your instruments on a string so that they can rotate or sway in the wind, rather than be rigidly fixed to a structure can add an additional element of randomization and aesthetic variation to an installation. A further consideration is whether your object is located where people might interact with it, like an instrument, or placed out of reach, to function more like a sound installation.

5) As with all solar powered projects, the environment the device is situated in controls its output. If you’re relying on natural light, the time of day and year, along with the weather, will impact how much sunlight your solar module receives. By considering the changes in the amount of sunlight over a given time period you can design projects that have new and unique characteristics at different moments.

This is a great project to build with upcycle old parts. As long as your solar panel and motor are relatively small, around 6 volts or less, there’s almost no risk of seriously messing anything up if your components don’t perfectly match. For my version, I used some scrap materials I had lying around the studio. It’s best to solder everything together, but you can definitely get by with alligator clips or other temporary methods.

As with any electronics project, but especially with something as variable as solar power, it is very helpful to test your components and electrical connections at every step of the process. Before you begin wiring your project test the voltage output of your solar panel with a multimeter.

Connect the positive terminal of your solar panel to the positive terminal of the motor and connect the negative terminal of your solar panel to the negative terminal of your motor. Depending on what type of motor you are using it may or may not matter which side is positive or negative. Think about how you might want to mount your project before you cut your wire to ensure that it’s long enough.

The most complicated aspect of this circuit is the diode. A diode is like a one-way street for electricity; it lets electricity flow in only 1 direction and blocks it in the other direction. The diode is a somewhat optional component in this particular circuit. When a diode is positioned across the terminals of a motor, as it is here, its referred to as a flyback diode. A flyback diode serves to safely dissipate current when the circuit is opened. It's generally a good idea to connect a flyback diode to any DC motor. The cathode side of the diode (typically indicated by a line on the diode) should be connected to the positive motor terminal. The other side, called the anode, should be connected to the negative motor terminal. It’s generally recommended to connect the diode as close to the motor as possible.

You can attach whatever you want to the motor shaft. I used a short length of 20 gauge steel wire. I attached it to the shaft by twisting on with pliers and applied a little hot glue on top. Try different materials. Heavier materials will cause your motor to spin slower, creating a different percussive rhythm and sound.

The distance of the motor and wire to the chimes was decided through trial and error.

Here are a few other direct drive projects of mine which can be found in the archive that use almost identical direct drive circuits.
Left) PV Bots - Instead of a standard DC motor, this project use a small vibration motor. Center) PV Sculpture Motion Study Right) Simplest Solar Sounder - This uses a piezo buzzer instead of a motor.