Conex Club Magazine - no.5 - 2006

Conex Club Magazine - No. 5 - 2006 - MAX712 / MAX713 - NiCd / NiMH Battery Fast-Charge Controllers

Reading time: 6 minute

The main topics presented

1. Indicator - universal controller for liquid level

Does it often happen that you or your friends (wife) forget the tap on the water tank or an open washing machine? How many times has your bathroom been flooded? Has the water level in the aquarium dropped or has the rain filled the water tank for collection? Do you often flood the cellar? A simple negligence and disaster follows!

The situations described above can be avoided by using, in the right place, the level indicator and controller designed and made by Velleman.

Three modes of operation characterize the K2639 kit:

  • optical level indicator;
  • automatic control of the liquid level in a tank (level controller);
  • alarm (empty or full tank).

Optical level indicator

If we refer to the first option listed, optical level indicator, three LEDs are used to signal the levels "low" - low, "medium" - medium and "high" - high, respectively empty pool, medium loaded or full!

Automatic control of the liquid level in a tank (level controller)

The assembly has a power relay on the PCB, with a pair of NO (normally open) / NC (normally closed) contacts, for 240V / 3A max.

The relay is activated when sensing the critical levels, "low" or "high", and through its contacts an electric pump or an electromechanical valve is controlled, in order to maintain the desired water level in a tank. This is the automatic level control function (level controller).

Alarm (empty or full tank)

If the sensor inputs are configured properly, the mounting can be used as a warning device (alarm signal), when the respective sensors detect a level below or above the allowed.

An electronic siren can be used as an audible warning device or a blue / red light (rotary, strobe) lamp as an optical signaling device.

2. Remote control receiver for switching electrical and household appliances

The circuit presented in the article can be used in households and facilitates on / off switching of the light bulb in the room, for example, using the remote control of the TV, DVD or any device controlled by an infrared remote control.

Thus, the TV remote control becomes an accessory with which you can control, from a distance (maximum 10m), the lighting in the room.

Receiver operating frequency TSOP1738 is 38kHz. The signal received from the remote control is captured by IC1, amplified by T1 and applied on the clock pin (14) of the counter CD4017.

3. Motion control in both directions at a DC minimotor

With a single push-button you can control the direction of rotation of a low-consumption DC motor. The output of the 555 can control loads with max. 200mA @ 15V (100mA @ 5V).

Three LEDs signal the movement of the motor in one of the directions of rotation (R + or R-) and the rest state (STOP).

U2 works as a monostable, to eliminate the influence of electrical noise when switching the push-button. Reset pin (15) of the counter 4017 is connected to output Q4, and Q0 and Q2 provide the same function (they are connected together by D4 and D2), so three states are possible, which follow one another in order: STOP, forward (R +), STOP and backward (R-) .

U4 and U5 work as bistables activated by the R + and R- commands, respectively.

4. MAX712 - controller for protected and fast charging of several NiCd or NiMH elements

MAX712 (and MAX713, with very small differences) is a Specialized integrated circuit for fast charging of NiCd or NiMh batteries from a DC voltage source.

From 1 to 16 elements (1,2V) connected in series can be charged, their number being programmed by hardware, by configuring the potentials at the PGM_ pins.

Fast loading is done from C / 2 to 4C (C = battery capacity).

The protected load (of "maintenance") with C / 16 is also available, the switching being done automatically, by the internal elements that determine the working logic of the circuit.

The detection mode of the end of charging is done by noticing the voltage slope, the battery temperature or by exceeding the required charging time.

Charging is performed in constant current. The element that provides information about the current state of the battery is the R-SENSE resistor.

After disconnecting from the voltage source, MAX712 consumes from charged battery max. 5uA. The supply voltage must be at least 6V higher than the total voltage of the batteries connected in series, subject to charging.

5. Measuring and recording the temperature on the PC - using the iButton DS1820

In industrial or agricultural processes, measuring and recording long-term temperature variations or temperature control, both hardware and software can be conveniently used using the PC and iButton components.

Electronics and PCs have been together for some time and have resulted in applications, sometimes simplistic, if viewed from the point of view of the hardware creator, applications that, without the use of the PC, would have required significant human and material resources. in the process of creation.

Measuring temperature at several points and recording data over a long period of time is a concrete example.

Simplified wiring, on two wires, the possibility to connect several sensors on the same two wires (in parallel), the identification of the sensor by its own ID (identification number), very low consumption.

These would be the most important characterizations of an iButton component designed to measure temperature.

The article presents applications that offer the possibility of measuring temperatures in several areas, using a two-wire network called MicroWire, to which several temperature sensors can be connected DS1820.

This sensor, in addition to the temperature measurement function, also has an internal memory in which attention limit values, upper or lower, can be stored.

Touching them will lead to the generation of an alarm code on the two-wire bus, which can be received by a software made on a PC.

6. Volumetric sensor (or broken glass detector)

The volumetric detector presented is able to detect instantly small variations in air pressure, such as forcing and opening a door or window!

By mounting this device in your home you get a instant warning device if an intruder tries to force the door or window (or break the window).

It is easy to understand that this assembly can be used both as a sensor for a complex alarm system, and to control the exterior or interior lighting in case an unwanted event is detected (attempted burglary).

Why volumetric sensor?

It is known that most sensors for alarm systems, and we list here infrared motion detectors (so-called PIR) or those that detect motion based on ultrasound (or combined, PIR + ultrasound), can not be activated to generate an alarm when the owners are in the house!

Well, there are sensors that allow the activation of the alarm system while we are in our own home: sensors that detect strong mechanical shock or those that detect the breaking of a window combined with changes in air pressure (which accompanies the event).

The latter, mounted on a separate entrance (called the zone) of the alarm control panel, will allow the partial reinforcement (home type) of the system, an active function during the night, for example, when the owners sleep.

But, as I mentioned above, the presented assembly can control directly, by means of a relay, either a siren or an electric lamp in case of detecting an event, and why not, even a processor with speech synthesis, which will reproduce in the speaker, a warning message for the intruder, making him withdraw!

A unique application can be the use of the installation in an office or a small store, as a warning signal in case a customer visits you.

Technical data:

  • supply voltage: 12Vdc;
  • relay output, NO / NC contacts;
  • relay activation time 10… 60s;
  • immediate or timed activation functions upon notification of the event;
  • delayed activation (approx. 10s) when powering the assembly, signaled with LED;
  • adjustable sensitivity.

7. 2 x 3W stereo audio amplifier

The kit presented is a AB class audio amplifier using BA5406 integrated circuit produced by ROHM.

Easy to make, with only a few electronic components, on a printed circuit board that can be made in a few tens of minutes, the audio signal amplifier made based on the BA5406 circuit can be connected without problems to most signal preamplifiers or to the output of sound cards. PC, its input impedance being high.

The power obtained is maximum if the assembly is supplied from a direct voltage source, well filtered, which can discharge in load, without problems, more than 1.5A and if a speaker with an impedance of 4 Ohm.

A minimum electrolytic capacitor is recommended when filtering the power supply 2x4700uF / 16V.

8. Voltage stabilizer 1.25… 20V / 4A

Although simple at first glance, the application stands out for its originality, a simple adjustment, limiting the maximum current charged in the load, in a wide range. The voltage stabilizer shown is a wide application of the LM317 integrated circuit.

Maximum allowable values ​​of LM317, at an ambient temperature of 25 ° C, are:

  • maximum voltage allowed at the input (unstabilized) = 40V;
  • the minimum allowed difference between the values ​​of the input and output voltages = 5V;
  • maximum allowable output current = 0.5A.

Please note that, for example, when we want to obtain a stabilized voltage of 5V at the output, the value of the input voltage (unstabilized) must be at least 10V.

To extend the value of the stabilized current to 4A, the power transistor was used, model 2N3055. Of course like this must be mounted on a suitable radiator that can dissipate a thermal energy of the order of 50… 60W.

In order to limit the amount of radiated electricity in the form of heat, it is recommended that the voltage applied at the input be higher than that at the output within the limits 5… 10V.

This condition is not mandatory. The flow current can be limited from the value of 2A, operating the semi-adjustable cursor R1.


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