Production of acoustic and optical digital level detector

This article introduces an acousto-optic digital level detector circuit composed of a 555 time base integrated circuit and a small number of peripheral components. The detector has good practical effect and is easy to make.

The detector circuit principle is shown in the figure. When probe A is floating, transistor BG is cut off, control terminal 5 of the time base circuit NE555 is at high potential, the controlled audio oscillator composed of NE555, R3, R4 and Cl does not vibrate, the speaker is silent, and pin 3 of NE555 The pin outputs a high level, and the LED is cut off and does not emit light, that is, the detector is silent and lightless. When probe A contacts the logic "O" level, pin 4 of the reset terminal of NE555 shows a low level, and the circuit is reset, so that the audio oscillator still does not vibrate and the speaker is still silent, but at this time, the output of pin ③ of NE555 is low level. flat, the LED is turned on and emits light, that is, the detector has light and no sound; when probe A contacts the logic "1" level, the ④ pin of NE555 becomes high level, and BG is turned on, causing NE555's ⑤ pin to become low level. The controlled audio oscillator starts to vibrate, the speaker produces sound, and the LED flashes and lights up, that is, the detector has sound and light. When the contact of probe A is continuous pulse, the LED and speaker will work alternately, that is, they will give sound and light instructions respectively.

The probe A of the detector can be made by making a suitable copper wire. The transistor can be a 3DK3 or 3DK7 switch tube. The LED can be a red light-emitting diode. The power supply can be a 6V laminated battery. All components are housed in a pocket radio case. When installing, pay attention to the location of the LED and speaker on the casing, and lead the probe and ground wire out of the casing.