How to make a simple high-impedance electromagnetic earphone?
Mineral radio is a project that is very suitable for primary and middle school students, but the earphones it needs are very sensitive. In the old days when rock radios were popular, there were high-impedance electromagnetic earphones for mineral receivers. Now this kind of earphones are difficult to use in ordinary I saw it in the electronics store. Some online shops that specialize in selling ore machine materials can also buy high-impedance headphones or high-sensitivity reed headphones, but they are all aristocratic, plus a courier of more than 10 yuan. Beginners have to spend dozens or even hundreds of dollars to buy a pair of headphones before they see a glimmer of light. It's really hard to make up your mind. Welding two wires from the piezoelectric sheet, of course, it is the most troublesome to use the original computer earphone wire. Then put it into the original shell, and a pair of piezoelectric earphones succeeded. Now you can use it to directly replace high-impedance headphones! Oh, it has to connect a 20kohm resistor in parallel at both ends to work properly. For example, you can take responsibility for the circuit in my article "How to learn how to install a rock radio for beginners". The piezoelectric earphone itself is high impedance, so there is no need to use a power transformer to change the impedance! 1. Decomposition: biodegradable excess body fat, flat meat, all kinds of stone decomposition, promote the decomposition of food digestion and absorption. Enzyme Essence Liquid,Liquid Promote Digestion And Absorption,Orange Enzyme Liquid For Health Guangdong ganzhou , https://www.tlqcjs.com
Here, I would like to introduce to you an easy-to-find cheap material to make a pair of piezoelectric headphones. Although the sound quality and volume are not very satisfactory, it is still reasonable as a popular equipment for making mineral radio sets for the first time.
First, find a piezoelectric film. The larger the diameter, the better. I got a 35mm piezoelectric film. See below: 
Find another pair of earphones for computers, open the cover from the front, and remove the dynamic earphones inside. Only the front cover is left. Use hard cardboard to make a ring, and glue the 35mm piezoelectric sheet to a diameter of 40mm, so that it is as big as the original dynamic earphone. 
Now the size of the piezoelectric sheet is exactly the same size as the front cover of the headset, and it is just glued to the front cover. 
Is this very simple? Make a pair quickly, the cost is only 1~2 yuan, that is, the money to buy a piezoelectric film! 
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