Showing posts with label two. Show all posts
Showing posts with label two. Show all posts
Tuesday, August 26, 2014
Basic Oscillator Circuit using Two Transistors
This is the schematic diagram of basic oscillator schema which using two transistors. When two transistors and a couple of passive components are connected as shown in the figure, the schema starts to oscillate. The frequency of oscillation can be adjusted by changing the values of either the resistor or the capacitor.
For easier experiment, you may replace the resistor with 10K potensiometer. By increasing its frequency to a suitably high level, it can be used to drive a speaker or a buzzer to produce an audio alarm note. By sufficiently reducing its frequency, the schema may be used to flash a LED as a warning indicator.
The another schema of two transistors oscillator described in the following video:
Thursday, August 21, 2014
Two Zone Burglar Alarm
Descrition
This is a two-zone alarm - with automatic exit, entry and siren cut-off timers. It can be triggered by the usual types of normally-closed input devices - such as magnetic reed contacts - foil tape - PIRs etc. Ive used a 12-volt supply in the diagram - but the schema will work at anything from 9 to 15-volts. All you need do is select a siren, buzzer and relay to suit the voltage you want to use.
Schematic Diagram
When you move Sw1 to the Set position - you have about 30 seconds to leave the building. If you re-enter through the Exit/Entry zone - the buzzer will sound - and youll have about 30 seconds to switch the alarm off. The Instant zone has no entry delay. Anyone entering through the Instant zone - will sound the siren immediately.
About ten minutes after the normally-closed loops have been restored - the siren will switch off - and the alarm will return to standby mode. It can then be re-activated by a subsequent intruder. If you dont want the siren to sound a second time - add the One-Time-Only Module. It forces the siren to switch off after the first ten minutes. And it prevents the alarm from activating a second time. This module has other uses - so its worth a look.
The various timing components are listed in the diagram. If you want to change the length of any of the delays - change the value of the capacitor and/or the resistor shown. Increasing the value of either - will increases the delay. And reducing the value of either - will shorten the delay.
Stripboard Layout
Subscribe to:
Posts (Atom)
