In the car a lot of devices that are included in the operation key or switch. To control the inclusion of a device only by clicking a mechanical switch (which when the machine can not hear) or visual position of a key (which is not easy in motion).
With the proposed electronic unit, the circuit of which is shown in the figure, it is possible to monitor the condition of electrical devices of the car powered from 12 V, which are characterized by two States: enabled/disabled a more dependable way — with a sound confirmation, which is very convenient for people with impaired vision (particularly “long-sighted”). Devices, both electrical and mechanical, for use of this unit in the car quite a lot: rear window defogger, manual and foot brake, reverse, etc.
The node is implemented on three popular circuits CMOS technology. When enabled, the monitored device alarm short beeps. The same happens when you disconnect the power.
The principle of operation of the device
Chip K561LA7 combines in one case four of the same item, And (with inversion). On inverters DD1.1, DD1.2 assembled generator of rectangular pulses. Its output frequency is specified in the diagram the RC-elements is about 900 Hz. From terminal 4 of the chip DD1.2 rectangular pulses are constantly fed to the input element D1.4 (pin 13) and terminal 12, the control signal comes from the chip К561ЛП2.
When a high level voltage at the output of the element DD3.1 rectangular pulses from the generator pass through a limiting resistor and amplifier on the VT1 transistor to the piezoelectric NA1 capsule type ZP-22 (you can use any primer with model number SN-x).
Sound amplifier on the VT1 transistor is required to signal to the piezoelectric capsule was well heard at a distance from the device itself. Transistor cascade supplemented by a volume control R4. As the transistor VT1 is suitable КТ503, KT361 with any alphabetic index.
When the output 12 of the control D1.4 is logic low, the output of this element, in accordance with the truth table microcircuits K561LA7, there is a logic high, which closes transistor VT1, so the emitter NA1 is not active.
The input signal is transmitted to point a (see diagram) with a controlled “load”. In this case, its parameters are not important — the main thing that it was a resistive load with a constant impedance. The input signal is synchronous with a clock oscillator frequency input From the first trigger and the signal in antiphase to the input of the second trigger. The synchronization process is reduced to the shear edge of the pulse input to match it with the front of the nearest clock pulse. The length of the converted information pulse will also depend on the duration of the pulse synchrodestiny.
Electric circuit device sound lights car consumers
The input high level signal supplied to point a and the input D of the chip DD2 (K561TM2), is permissive to the true output Q (pin 1 of the first trigger DD2.1) synchronously with a clock of rectangular pulses coming from the generator, there is a high level signal and were present as long as the high level at point A will not disappear. At pin 13 of the trigger circuits K561TM2 (direct access trigger DD2.2) at the time of the appearance in A high-level voltage is also set high. It will change to low with the arrival of a negative clock edge following the disappearance of the high-level voltage at the point A.
The output of the element DD3.1 are formed two pulse attached to the front of the input signal. Short pulses at the point D will correspond to the time of appearance and disappearance of the high-level voltage at point A due to turning on and off of any consumer.
Assembled from serviceable details are presented of the electronic Assembly in adjustment is not needed. Immediately after Assembly it needs to be tested together with stabilized power supply constant voltage 12 V. Included in this way a node should not emit a sound signal. If you apply to the input And the circuit voltage of the power supply needs to earn short-term sound emitter NA1.
Details
Fixed resistors type MLT-0,25. Variable resistor R4 — type SP5-1ВБ.
The current consumed by node in sleep mode is 8 mA, the sound mode display — depends on the type of emitter used, but does not exceed 25 mA.
A. KASHKAROV, St. Petersburg
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Buzzer on digital circuits switching on/off of electronic devices with power supply of 12 V.