Simple and practical touch desk lamp

The components of this circuit are 555 as the main control chip. This is the most classic touch desk lamp circuit, and the price is not expensive. The single-pole plate touch is completed through RC discharge. The size of the capacitor and the resistor determines the time the light is on. But this has another disadvantage. When you touch it, the light turns on, but it cannot be turned off. You must wait until the RC discharge is completed. If the RC is set shorter, it sometimes requires frequent touches, which is not very convenient.

Is there a circuit that can make him touch the light once and turn it off again? You may have thought of the bistable trigger circuit. This circuit has two output states, either 0 or 1, and the power consumption is very low. Just add an amplifier circuit in the front stage, which is simple and practical.

The control circuit is to use weak current to control strong current, which is nothing more than a thyristor or a relay.

Relays are used here, and double isolation is used to ensure that even if there is a problem with the circuit, people will not get electric shock when touching it. This is very important.

There are mainly three types of power supply designs: one is the transformer; the second is the resistor and capacitor in series to step down the voltage; the third is the switching power supply.

The use of a transformer has good effects, but its disadvantages are that it is large in size and there are power consumption and heat generation problems when powered on for a long time.

Resistor and capacitor voltage reduction should not be used, as they are inefficient and dangerous. Let me tell you that the current mobile phone and MP3 charger actually has a small switching power supply, which can be turned into a good power supply with a little modification! Through actual modification and measurement, the voltage is increased to 9V, which can fully drive the relay. This method is characterized by low power consumption. Even if there is a short circuit in the actual welding experiment, there is no problem. Moreover, the touch plate is powered by 9V electricity, which is very safe for the human body.

Since it involves touch, it must involve safety issues. Most designs are single-pole plates. Once the plate is mistakenly connected to the live wire, the current will pass through the finger and body to the ground when touched, forming a loop and causing electric shock. That's why bipolar plates are used, one end is connected to the negative pole and the ground wire; the other end is connected to the input end of the amplifier circuit, and only a small part of your finger that touches the conductor is energized.

Now the basic framework has been formed. The circuit is organized as follows:

The circuit components are all common components, very suitable for self-made, and the circuit is relatively simple, so I didn't draw a PCB (printed circuit board) board diagram, and just used a test board for soldering! First make a finished board, and the experiment proves that the effect is good. The plate is the bottom dial of a waste multimeter, and connects the two adjacent rings. You can also use two wires placed in parallel!