A small improvement to the temperature and water level indicator alarm

1. Generation of warning sound.
Disassemble the original water level indicator alarm and modify it into the circuit shown in the figure above.
2. Output a positive pulse circuit of about 1Hz every 20s
. This circuit can use a timer integrated circuit NE555. This functional circuit is shown in the figure below. The diode on the right side of the group is mainly used to separate the charging and discharging circuits in this circuit to form an oscillation circuit with adjustable duty cycle. The calculation method of the oscillation frequency is: f=1.44/(10 to the fifth power + 2×5×10 to the fifth power)×10 to the negative sixth power≈1.3Hz.

3. Welding and debugging

The volume of all components in the figure below should be as small as possible, and then welded on a small circuit board, stuffed into the idle space of the original machine box, and the positive and negative poles are connected to the positive and negative poles of the original circuit respectively. The AB line segment in Figure 1 can be cut with a knife on the back of the original printed circuit board, and then the diode is directly welded to the two ends of the break point on the back (note: the positive and negative poles of the diode should not be connected to germanium), and the output in Figure 2 is welded to point A in Figure 1 with a wire. This circuit can be successful as long as the components are of good quality (especially the 10μF capacitor cannot have leakage), and the welding is correct, and no debugging is required.