Practical Blind Hearing Voltmeter: Traditional Chinese Circuit Design
In short: Traditional Chinese Practical Blind hearing voltmeter. This entry documents a circuit & prototype taken from Chinese practical-technology literature, written for small-scale makers and home producers. The text below is the full English translation of the original Chinese workshop notes, covering materials and quantities, the step-by-step sequence, and the practical cautions recorded in the source. Roughly 1876 words of English technical text, translated and preserved without editing. It is intended for experimental and reference use, not for regulated or commercial certification.
Hearing voltmeter for blind peopleThe blind hearing voltmeter circuit shown in Figure 120 consists of a DC amplifier, an audio oscillator and an output amplifier.Figure 120The two input terminals of the voltmeter are connected to the input terminals of the DC amplifier. The DC amplifier consists of transistor VT1. The signal amplified by VT1 controls the audio oscillator composed of VT2. The output signal of VT2 is amplified by the output amplifier composed of VT3, and excites the speaker BL to produce sound.The frequency of the VT2 oscillator is proportional to the analog voltmeter reading. When switch S2 is moved to the calibration position, the input voltage of the DC amplifier comes from the voltage divider formed by DC1 through potentiometers RP1 and RP2. At this time, the frequency of the oscillator is controlled by RP1 and RP2.There is a large dial under the potentiometer RP2 knob with Braille (voltage value) engraved on it, which can provide usage conditions for blind people. Therefore, a blind person can read the corresponding voltage value by touching the dial.When using it, first dial S2 to 1 (positioning) and listen to the tone in the speaker, then dial S2 to 2 (calibration position) and adjust RP2 so that the tone in the speaker is the same as that in "positioning". You can turn it back and forth several times. When the tone is consistent, a blind person can know the measured voltage by touching the braille on the RP2 dial.Another use is to adjust the voltage value of the circuit by first adjusting the electrical position RP1 to the desired reading, and then adjusting the device under test until S2 is toggled back and forth between the two positions without the tone remaining the same.Capacitor C5 in the circuit is selected according to the lowest required frequency, …
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Lei Cheng
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Lei Cheng