In "Radio", 2000, No. 10, pp. 33, 34, was published the article of O. Searchgo "Simple car watchman," describes a very successful device for protection of the car. It was me, repeated many times, in this design some changes were made aimed at improving operational properties.
Thus, if the output element 6 DD3.2 (according to the scheme mentioned in the article) disconnect from output 5 and other circuits and connect to pin 1 of the flip-flop DD2.1, when the trigger guard HL1 led stops flashing and illuminates continuously. After occurrence of the guard in the protection mode, the blinking of the led is restored.
This transformation facilitates the monitoring of the device status.
The article says that when applied to the watchman of the supply voltage will be generated pulse with a duration of 400 MS and a short beep signal indicating the inclusion of a security device. But this signal is, in fact, contributes to demaskirovanie of the switch.
To avoid this, have been proposed and tested in practice two ways. First - to exclude a single-shot DD3.3, DD3.4. Second, have proved more acceptable, - to enable the guard open the switch, it triggers a further mounted relay K2 (see figure), and turn off the relay and the guard a hidden button.
To activate reed switch used SF3 is mounted behind the windshield, near alarm led HL1. Coming out of the car, the driver applies to outside the glass in front of a small reed switch, the magnet closes the reed switch. The voltage arrives at autostorage and the relay coil K2. It works and contacts K2.1 blocks the reed switch. Now the magnet can be removed, the guard and the relay will be powered through contacts K2.1, and the relay coil through the resistor R16, handpicked his current the deduction. Off guard with a hidden button SB1.
At the described method of incorporating a security device delay time for joining him in guard mode becomes unnecessary, so the capacity capacitor C2 can be greatly reduced. It should be borne in mind that the specified the revision increases the current drawn from the battery mode protection. But since relay K2 commutes small current, you can use reed relays, for example, RASA (passport RS4.569.602 or RS4.569.607), or miniature usual, for example, RAS (passport RF4.500.407-01 or RF4.500.407-05).
In the original version of the watchman at operation of any alarm sensor alarm the alarm starts to sound after a certain time delay. More correct would be the mode in which the alarm is triggered with a delay when you open the door the driver and immediately upon opening any other doors, bonnet and cap trunk, breaking the Windows of the cabin, etc., This mode is easy to implement if the anode of the diode VD5 guard disconnected from the pins of the chip DD3 and to connect the output item DD1.1 (pin 3).
Now the alarm will sound at the time of contact closure SF2 (it's all the sensors, in addition to the sensor driver door). If now the contacts SF2 open, the alarm will stop, but the duty cycle watchman fully work and will be back again in protected mode. During installation of updated version of the watchman in charge don't need to install a capacitor C7 and a resistor R13, a conductor connecting the anode of the diode VD5 with chip DD3, need to remove and empty the inputs of the elements DD3.3 and DD3.4 connect the positive to the positive power wire.
The sensor SF1, the device will still respond with a delay.
Author: A. Maravich, Voronezh