Integrated CD4013 touch switch design

This circuit uses the CMOS integrated circuit CD4013 double D flip-flop, which is connected into a monostable circuit and a bistable circuit. The function of the monostable circuit is to shape the pulse width of the touch signal to ensure that each touch action is reliable. The bistable circuit is used to drive the transistor Q1 to open or close, and then control the relay.

Here are the basic original images found:

But we also referred to some other related circuits, added the power filter capacitor and LED indicator, and changed the input to 2M resistor to ground. Changing it can change its sensitivity. After a small modification of the circuit, the following figure is the full picture of our production.

M is the touch electrode. When you touch M with your finger, the AC leakage from the human body will drop on R4. Its positive half-cycle signal enters the 3rd pin of IC1, i.e. the CP end of the monostable circuit, causing the monostable circuit to reverse and enter the instantaneous state. Its output terminal Q, i.e., pin 1, changes from the original low potential to a high potential. This high potential charges C2 through R1, causing the potential of pin 4, i.e., the R1 end, to rise. When it rises to the reset potential, the monostable circuit is reset, and pin 1 returns to a low potential. Therefore, every time you touch the electrode M, pin 1 outputs a positive pulse with a fixed width. This positive pulse will be directly added to pin 11, i.e., the CP end of the bistable circuit, causing the bistable circuit to reverse once, and the potential of its output terminal Q, i.e., pin 13, will change once. When pin 13 is at a high potential, the base of Q1 obtains a forward current through R2 and turns on, causing the relay to operate, and then its contacts are used for control. It can be seen that every time you touch the electrode M, the relay can be turned on or off.

Component selection and production, CD4013 dual D flip-flop digital integrated circuit, it uses 14-pin dual in-line plastic package. Q1 can use low-power NPN transistors such as CS9013 or 2SC945.

Attached below is the pin diagram and truth table of CD4013:

The following is the circuit board LAUOUT and parts configuration diagram:

*Red line is jumper

The following are photos of the finished product:

Note:

I found some problems in the actual production, and there are a few points I want to explain to you in particular:

1. Try to use the mains power supply to obtain 12V power through a transformer to reduce the voltage: I found during the practice that if the battery is used for power supply, sometimes it cannot be triggered. Analysis may be that when the battery is used for power supply, the circuit itself has no actual connection with the earth, resulting in the AC leakage from the human body to the earth not being related to the grounding of the circuit, so the voltage entering the touch point also becomes smaller.

2. During production, I also found that some ICs were too sensitive and sometimes malfunctioned, so I added C4 to the circuit. Do not solder C4 when soldering parts. During testing, if you find that the action changes when the touch piece is not touched (sometimes it happens when switching fluorescent lamps, you can try it yourself), then add C4. You can even lower the value of C4 when the circuit does not function when touched, or increase the value of C4 when malfunctions still occur, to find the most stable value.

3. The touch points must be connected into a touchpad. Do not use wires directly instead, because the contact area with the human body will be too small, which will affect its sensitivity.

4. The input-to-ground resistance R4 (2M) will also affect the sensitivity. If it is found to be not sensitive enough, the 2M resistance can be increased, such as 2.7M.