Series and parallel speaker connection options for a stereo headphone plug. Step 1: First, solder wires to the headphone jack. The headphones will most likely have a three-contact plug with a common input and separate left and right speaker inputs for stereo sound. You may either connect the two stereo speakers in series or in parallel, as demonstrated in Figure 2.įigure 2. Learn how to use diodes to clip voltage at some maximum level. Learn how to use a potentiometer as a voltage divider/ signal attenuator.To show how to detect extremely small electrical signals.A linear-taper potentiometer works quite well. The 100 kΩ potentiometer is a recommended option for incorporation into this project, as it gives the user control over the loudness of any given signal.Įven though an audio-taper potentiometer would be appropriate for this application, it is not necessary. The tolerance (precision) rating for the 1 kΩ resistor is irrelevant. Beware, as you could spend hundreds of dollars on a pair of headphones to get the absolute best sensitivity. Take heart, though, I’ve used an old pair of Radio Shack Realistic brand headphones with perfectly adequate results, so you don’t need to buy the best.Ī transformer is a device normally used with AC circuits to convert high-voltage AC power into low-voltage AC power and for many other purposes. It is not important that you understand its intended function in this experiment other than it makes the headphones become more sensitive to low-current electrical signals. Normally, the transformer used in this type of application ( audio speaker impedance matching) is called an audio transformer, with its primary and secondary windings represented by impedance values (1000 Ω: 8 Ω) instead of voltages. An audio transformer will work, but I’ve found small step-down power transformers of 120/6 V ratio to be perfectly adequate for the task, cheaper (especially when taken from an old thrift-store alarm clock radio), and far more rugged. If you’re serious about building a detector with maximum sensitivity for small electrical signals, you should try a few different headphone models at a high-quality audio store and listen to which ones produce an audible sound for the lowest volume setting. Regarding the headphones, the higher the sensitivity rating in decibels (dB), the better, but listening is believing. Two banana jack-style binding posts or other terminal hardware for connection to the potentiometer circuit.Small step-down power transformer (using the 6 V secondary winding tap).Headphone jack female receptacle for headphone plug.High-quality closed-cup audio headphones.One recommendation is to build this detector in a permanent fashion (mount all components inside of a box and provide nice test lead wires) so it may be easily used in the future. It is also valuable in that it allows you to use a different bodily sense (hearing) in interpreting the behavior of a circuit. A voltage detector is a valuable piece of test equipment, especially for the low-budget experimenter without an oscilloscope. Voltage detectors are intended to be used for balancing bridge measurement circuits, potentiometric (null-balance) voltmeter circuits, and detecting extremely low-amplitude AC (alternating current) signals in the audio frequency range. Completed voltage detector with adjustable sensitivity and audio output. In this project, you will learn to build a voltage detector with audio output to headphones and adjustable gain sensitivity, as illustrated in Figure 1.įigure 1.
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