易家电子 - 请牢记网址 www.ejdz.cn !

易家电子-(www.ejdz.cn)

当前位置: 主页 > 电子工程 > 555电路 >

Water Activated Alarm

时间:2009-05-30 17:52来源:未知 作者:admin 点击:
The circuit uses a 555 timer wired as an astable oscillator and powered by the emitter current of the BC109C. Under dry conditions, the transistor wi

The circuit uses a 555 timer wired as an astable oscillator and powered by the emitter current of the BC109C. Under dry conditions, the transistor will have no bias current and be fully off. However as the probes get wet the transistor will conduct and sounding the alarm.

易家电子

An On/Off switch is provided and remember to use a non-reactive metal for the probe contacts. Gold or silver plated contacts from an old relay may be used, however a cheap alternative is to wire alternate copper strips from a piece of veroboard. These will eventually oxidize over but as very little current is flowing in the base circuit, the higher impedance caused by oxidization is not important. No base resistor is necessary as the transistor is in emitter follower, current limit being the impedance at the emitter (the oscillator circuit). www.ejdz.cn

 

织梦二维码生成器
易家电子:微信公众号
顶一下
(0)
0%
踩一下
(0)
0%
------分隔线----------------------------
栏目列表
推荐内容