Conex Club Magazine - no.10 - 2003

Conex Club Magazine - no. 10 - 2003 - Programmable keyboard

Reading time: 5 minute

The main topics presented

1. Programmable keyboard

Have you ever wanted a customizable keyboard, with buttons on which you can enter your own graphic symbols and which behave differently depending on your needs?

If so, this kit is the solution you need. A short sound is emitted when each key is pressed, and a pleasing visual effect is obtained with the help of a light source placed behind the keyboard..

The application presented is a keyboard with 8 capacitive keys, which can be customized according to everyone's needs.

The facilities offered are:

  • 8 keys with touch operation; LED status indicator for each key, respectively output;
  • the keys can be set to have or not to hold (a hold key, once pressed, maintains the status of the output until a new press, while one without holding activates the output only as long as it is pressed);
  • backlight with normal or low intensity (stand-by);
  • audible confirmation when a key is pressed;
  • 4 selectable hardware operating modes, by jumpers;
  • 8 independent keys (with or without hold);
  • 8 keys that work on the principle found in old radios: pressing one button means releasing all the others, so that at a given time only one button can be pressed (in English "radio-buttons").
  • 4 "radio-buttons" and 4 independent keys;
  • one key has the function of saving for the other 7 or resetting.

2. Remote control by phone

MK160 is a remote control operated via cell phone, whose possible uses are: starting the lighting or heating system, opening the doors of a garage, controlling the automatic feeding device for pets, removing people who have thought badly of their personal home, making them believe that someone is at home, activating a car alarm, etc.

The execution of the execution element (relay) is done by means of the phone backlights. Upon receiving a call, they light up and a photosensitive element (photoresistor) notifies the event.

The generated signal is processed at an appropriate level, to be interpreted by the microcontroller PIC12C508A which, depending on the settings, executes a certain part of the program from memory and commands the closing or opening of the contacts of a relay. Phones whose lighting is flashing during the call cannot be used with this kit.

There is no need to establish a telephone connection. A simple call is enough, which means that the bill will not be charged with anything extra.

It is also not necessary to modify the mobile phone or connect the mount to it via cables. The MK160 is compatible with most cell phones on the market.

3. Indicator for powering glow plugs

Starting Diesel engines in the winter when the temperature drops below 0C can be difficult. With the help of incandescent spark plugs, the problems that appear can be solved to a large extent, but their use must be done with caution, respecting the supply time with electrical voltage, specified by the manufacturer.

The supply of incandescent spark plugs for a longer time than recommended, on the one hand leads to a shortening of their lifespan and even to their burning., and on the other hand to the overload of the accumulator battery which in the conditions of low temperatures significantly diminishes its nominal capacity.

The presented installation warns the driver on the existence of the supply voltage of the spark plug at its terminals - by continuously lighting an LED, and after the recommended heating time - by pulsating lighting of the same LED, on the fact that the supply voltage of the spark plug must be switched off and the electric motor can be operated in order to start.

The wiring diagram is given in figure 1 (from the article) and contains two very widespread and at the same time very cheap integrated circuits: a 555 timer and a circuit CMOS type 4011 which encapsulates four classic YES-NO gates.

The supply of the assembly is made directly from the supply voltage of the spark plug (+ 12Vdc), the current consumed being approximately 25mA.

4. Soldering hammer with adjustable temperature

Although it will not be one of those modern devices with a stabilized peak temperature, this assembly can transform an ordinary letcon, of 220V, into a letcon with variable peak temperature, through the variation of the dissipated power in the heating resistance.

With such a letcon it is now possible to do the soldering of large electronic components or on surfaces with important thermal constant - areas that require high power, as well as a soldering of fineness, to a delicate connector or on a thin path of the plate, where imposes temperature limitation by limiting the power on the heating element.

Without solving the problem of thermostating the soldering tip, the presented solution offers the advantage of converting existing soldering hammers into letcones at which the temperature can be varied continuously between certain limits.

Of course, for a mounting of this type you can also use the classic voltage variator with triac and diac, but the diagram here controls the temperature not by varying the phase angle, but by varying the number of half-periods applied to the heating element.

5. Clock in 24h format - with 4-digit display

A time and date display system can be easily achieved using the CNX168 (24 Hour Clock) and CNX172 (4-digit Clock Display) modules. The two modules are easily interconnected, resulting in a small clock, panel or table clock.

With modifications to the interconnection system of the two modules, the use of a 4-digit display of other sizes (larger), a power supply suitable as power for the watch and, especially for the larger display, and a custom case, is can make a network of watches such as those mounted in large intersections of cities or markets.

The watch that we propose to be made by amateur manufacturers offers a good reliability, being made with an AT series microcontroller (from Atmel) that can be controlled by a crystal with various oscillation frequencies (4, 10 or 20MHz).

The time display is made in 24 hour format, respectively HH: MM, multiplexed on a 4-digit display. Optionally, the date can also be displayed in LL: ZZ format. The watch also has two alarm outputs.

6. Power outage indicator

Power outages, even for very short periods of time, can sometimes have unwanted effects: resetting personal computers or flickering on monitor screens, losing settings made for air conditioners, disrupting the clocks powered by the power grid and not they have power supply systems with buffer batteries, etc.

The signaling of such situations is therefore useful, and the cause of events such as those presented above can be quickly detected.

The basic component of the assembly is the integrated circuit 4013, which contains two D-type flip-flops. Of these, only one is used, and by connecting the clock (CK1) and data (D1) terminals to ground, it is transformed into a classic RS flip-flop. Its operation is shown in table 1 (from the article).

7. TL783 - High voltage stabilizer

Ordinary integrated voltage stabilizers, which we all know, can provide direct voltages of up to 30V at the output. But there are applications where we need higher voltages.

The article presents a high value adjustable positive voltage stabilizer, between 1.25V and 125V. This is the TL783C integrated circuit.

It is intended especially for high voltage applications, where most of the integrated 3-pin voltage stabilizers cannot be used.

The electrical characteristics of the TL783C are the following:

  • maximum input-output voltage difference: 125V;
  • maximum output current: 700mA;
  • continuously dissipated power (at 25C): 2W;
  • maximum junction temperature: 125C;
  • output voltage stabilization coefficient (between 15mA and 700mA): max 25mV or max 0.5%;
  • residual noise: 0,003 °%;
  • minimum stabilization maintenance current: 15mA;
  • voltage reference: typical 1.25V (minimum 1.2V and max. 1.3V).


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