Polarity discrimination of crystal diodes 3

Use batteries and speakers to distinguish the positive and negative terminals of diodes, as shown in Figure 6. Connect a battery and a speaker (or earphone) in series with the tested diode to form a series circuit. Then intermittently touch one end of the diode lead with the horn, and measure the diode upside down again. Based on the louder sound of 'lo, lo', the lead wire connecting the positive pole of the battery is the positive pole and the other is the negative pole diode