The Smart Switch
The purpose of this project is to build a smart switch
A smart swith is a swith that needs a short press and the power will be turned
ON.
If I press the button longer than 0.5s the power will shut down.
All contribution to this page
are most welcome!
Background
Why not using switches with two
way?
Thoose swithes need a arm and are quit big. With this smart switch unit you
can buy any simple low-flat, low cost one-way swith and still get a very impressive
function.
In my comming bug equipment I am going to use a small flat box and I am going
to use a flat button for power control.
Schematic
Imagin the power is off and the capacitor C1 is not charged. Q3 will be open
and no current flow.The Base of Q2 will be low and the Base of Q3 high. The
circuit is in stable condition, nothing is happening. If I press SW1 power
will flow through the diod and to the base of Q2. Q2 will conduct so the base
of Q3 will go low and the transistor Q3 will conduct and current go through
this transistor and keep feeding the transistor Q2. The circuit is locked
to deliver power to the output.
At the same time you press the SW1 button capacitor C1 will start to charge
through resistor R1. If the voltage is higher than 0.7V the transistor Q1
will start to conduct and pull down the current through the base of Q2. This
means that when you let the SW1 button go off the Q3 will not be conducting
and the circuit is shut down.
The time befor the circuit is on and off is determined by the value of R1
and C1.
You will have to experiment yourself. It depends on wich transistors you are
using, and you can use almost any transistors. Make sure the Q3 transisor
can handle the current you are going to draw through it.
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