555 electronic guide speaker circuit diagram for blind people

As shown in the figure, the 555 and its surrounding components form a voltage-to-frequency conversion circuit. The device used to determine the orientation of the Earth's magnetic field is a Hall effect integrated sensor UGN-3501M. The sensor contains a Hall unit and a linear differential amplifier. The sensitivity of the device is about 1.4 millivolts/Gauss. In order to improve the measurement The sensitivity of the earth's magnetic field, two flat magnetic rods are placed close to both sides of the sensor to detect more earth's magnetic field lines. The differential output terminals of the sensor (pins 1 and 8) are respectively connected to the inverting terminal (pin 2) and the non-inverting terminal (pin 3) of the differential amplifier composed of uA741, which is further amplified and then added to 555. The output voltage of IC2 depends on the strength of the magnetic field picked up on the Hall device, and the pulse frequency output by the voltage-frequency converter composed of 555 depends on the charging voltage value on C2. In other words, the output frequency is Determined by the position of the guide speaker. When adjusting, adjust the potentiometer RP1 so that when the magnetic field intensity is zero, the pulse frequency of 555 is a certain value (such as 1000Hz). When the orientation changes, the frequency changes due to the change in the magnetic field. The blind person can adjust the frequency according to the change in the tone. , determine the walking direction.