Traditional Chinese Adding hearing aids to the ULN-2204: Circuit Design, Parts List & Workshop Prototype Guide
In short: Traditional Chinese Hearing aids on the ULN-2204 monolithic radio (Workshop Practice) — Circuit, Wiring & Debug Guide. 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 1083 words of English technical text, translated and preserved without editing. It is intended for experimental and reference use, not for regulated or commercial certification.
Adding hearing aids to the ULN-2204 monolithic radioULN-2204 is a single-chip FM/AM radio integrated circuit. FM/AM radios assembled from it are small in size, have good sound quality, and are widely used in society. If an electret microphone is added to the machine, it can also be used as a hearing aid. The modification method is: because its detection output signal is derived from pin ⑧, it is sent to the input pin ⑨ of the audio amplifier through the volume control circuit (Figure 144-1). Cut off the connection between pin 8 of the circuit and the volume potentiometer, and use a double-pole double-throw switch for control. One of the poles is used to convert the audio input, and the other is used to control the power of the electret microphone (Figure 144-2). When the switch is thrown to a, it is used as a radio; when the switch is thrown to b, it is used as a listening aid. When used as a hearing aid, it is not advisable to use the built-in speakers and use earplugs instead. Otherwise, self-excitation will occur.(Qian Ruzhu) alt="209.jpg (14221 bytes)">Figure 144-1 …
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