Displaying the position of an execution element, such as the axis of a motor that drives the supporting pole of an antenna or the bending mechanism of a metal bar at a precise angle, an operation that has a high degree of repeatability in construction, can be done electronically by readers made with slotted optocouplers.
Proposed application can monitor up to 100 positions along a circle.
Two constructive variants are proposed which differs by the number of monitored (and displayed) positions on the shaft, the display mode and the way in which it returns to the initial (reference) position in case of accidental "fall" of the electric current.
3. Interface for controlling a DC motor
The presented application allows the control of a direct current motor, of low power, in both directions of rotation, provided with stroke limiters.
The most common direct application is operating a garage door or gate, moving on a sliding rail. The authors designed the mechanical system for transporting a very light assembly, on a rail mounted horizontally, similar to that of the conveyor belts in the production halls (keeping the proportions).
The article will refer only to the electronic block, because it has the character of universality. The mechanical part is particular to each application.
The construction of the electronic part involves the realization of two distinct blocks: the command interface and the power driver, respectively.
If at first sight things are somewhat nailed from a functional point of view, at the power block there are various constructive variants, based on transistors or relays, so that the power of the controlled motor can differ, without changing the control part.
As applications are remembered control of a gate or control of a modeling device, so both the industrial field and the entertainment.
4. Electronic key with Smart Card (phone card)
A used phone card (generically called a Smart Card) can also be used successfully to create an access control system.
A phone card is now a commonplace object, used by many people, for example when making phone calls from a public telephone.
On the card, there is a prepaid credit; when this credit is exhausted, the phone card no longer has any use and is thrown in the "trash". With a little imagination, the phone card (with and without credit) can be used as an electronic key.
5. Proximity sensor with CD4011
Using an integrated circuit CD4011 a proximity sensor is made which acts near an antenna object.
The first floor is an oscillator, whose oscillation frequency is adjusted from the semi-adjustable 500 Ohm. The oscillations are dependent on the signal captured by the antenna, respectively the one on the 4.7 kOhm resistor.
The two diodes 1N4148 forms a signal rectifier from the oscillator and together with the capacitor 0.22uF a peak detector (maximum) of it. If this signal exceeds the tipping threshold of the last gate NAND 4011 (pins 8-9), The LED is activated.
The presence of an object or a person is done with an LED controlled by a transistor 2N4123 (this can also be a 2N2222, 2N2219 or even BC547 or BC171).
