The main topics presented
1. Battery monitors
Monitor for voltage equality at the terminals of two 12V batteries
Most systems powered by 24V with a backup source (fire stations, ship models, etc.), use two 12V lead-acid batteries (encapsulated).
The charging system of the voltage source monitors and maintains the nominal sum of the voltages of the two accumulators. If one of the batteries fails (discharging more than the other, being at the end of its life) the system does not detect the event, unless the amount is much too small.
In this situation, the battery in good condition may be damaged prematurely!
Using the proposed monitor, mounted in the system, it can be detected in time if one of the batteries has a different voltage than the other. It is in fact a circuit that monitors whether the voltages at the terminals of the two batteries are equal, by detecting the voltage difference.
Status indicator for 6V batteries
The circuit provides an optical, progressive indication of a 6V encapsulated lead-acid battery (or four 1.5V batteries inserted), using as an indicator a L59EGW bicolor LED (red / green).
By combining the two emitted colors, an indication is obtained from green (good battery) to red (discharged battery), passing through an intermediate state, signaled with shades of orange.
The circuit can be modified very simply to signal the status of a 12V battery.
Indicator for discharged battery
LED D4 illuminates when the voltage applied to the circuit input drops below the prescribed value with the help of the semi-adjustable R3.
It polarizes at the base Q4, under normal conditions, it being open and blocking Q2 by the CE voltage lower than the opening voltage of the junction assembly BE Q2 - R10 - LED D4.
If the voltage drops below the prescribed value, Q4 locks, and Q2 is correctly polarized at the base by R4 and the LED signals red - low battery!
The circuit is calibrated with an adjustable voltage source and a digital voltmeter, connected to the input and the corresponding adjustment of R3.
2. 200W bridge amplifier, with TDA2030
Powered by well-filtered DC voltage, between +/- 24 and +/- 36V, on a load of 4… 16 Ohms, a maximum of 200W audio power can be obtained.
The played tape is 20Hz… 20kHz, and the input sensitivity of 500… 800mV. The maximum current consumption from the voltage source is 5A, so the (double) voltage source must be well dimensioned (transformer over 350VA, min. 2x40V, rectifier bridges of min. 5A, filter capacitors of 10000uF / 50V , cables for connections with a minimum section of 1.5mm2, fuses for protection, etc.).
From a thermal point of view, all transistors and integrated circuits will be mounted on one aluminum radiator with thermal resistance less than 1 ° C / W, respectively with minimum dimensions of 20 x 10 x 4cm.
The wiring is made for the transistors from the KT_ series (ECB configuration), for those from the BD_ series (BEC configuration) the position on the wiring will be reversed.
But models can also be used BD712, BD912, BD810 (for PNP), respectively BD711, BD911, BD809 (for NPN).
3. MC1496 integrated circuit
MC1496 integrated circuit (equivalent to MC1596 and N5596) was initially produced by MOTOROLA, later taken over by other manufacturers. In Romania, the equivalent type was produced at ICCE ROB796.
The function performed by MC1496 is generically titled "modulator - dual balanced broadband demodulator". This function is recommended for all applications where the output voltage is the product of two input signals.
- amplitude modulator with normal spectrum (complete), or with suppressed carrier (for SSB, DSB);
- double balanced mixer;
- synchronous detection;
- demodulation of amplitude, frequency and phase modulated signals;
- frequency doubling;
- amplification in HF - VHF.
4. Alarm and / or fire alarm control panel with 2 zones
The financial effort for the acquisition of complex (professional) alarm systems is important, but if the value of personal property is taken into account, it is perfectly justified.
An alarm and / or fire warning application is recommended (depending on the configuration), at which realization costs are modest and the satisfaction of the result is probably very high.
The assembly is also a foray into the use of SMD components in amateur mode.
Electronic assembly offers the following functions (depending on the connection mode of the two available inputs):
- burglary warning;
- warning at the beginning of the fire;
- emergency (panic) or warning of sabotage in the system (sectioning the cables when the system is armed).
For the warning of burglary attempts, the boiler has two inputs (currently called zones and marked NC - or NO - and PIF), which have as reference the mounting mass (marked C).
These inputs are either of the normally closed loop type, respectively the NC or PIF areas (to which the sensor outputs are connected in series), or open (NO input, to which the sensor outputs are connected in parallel).
5. Voltage inverter - 24Vdc / 220Vac, 50 / 60Hz, 350W
Wiring diagram of the voltage inverter in configuration "Push-Pull" is presented in figure 1 (from the article) and was developed in order to supply some alternative voltage equipment starting from a direct voltage of 24V, supplied by a battery.
The inverter can be used on board trucks or trucks, powering mini-refrigerators, electric kettles, chargers for mobile phones or any other electrical appliance whose electrical power does not exceed 350.
The main features are the following:
- supply voltage: 22… 28Vdc;
- output voltage: 220… 230Vac, rectangular waveform;
- output voltage frequency: 50 or 60Hz (selectable by jumpers and optically signaled by LEDs of different colors);
- does not require frequency adjustment;
- guard interval in control of the output MOSFET transistors;
- galvanic isolation by transformer, between the accumulator battery (or the electrical installation of which it is part) and the equipment supplied at 220V;
- stand-by function;
- optical indicator for discharging the battery, with the possibility of adjusting the warning threshold;
It is the main component the AT90S1200 microcontroller based on a quartz crystal with a resonant frequency of 4MHz.
6. Electronic timer with "start" and "stop" commands
You can order any electrical appliance in an automation application that requires timed operation, using the electronic timer with "start" and "stop" commands made by Velleman in kit (unassembled). The delay time is adjustable in the range 0.1s… 5min.
Physically realizing the application proposed in this article, will result in a programmable timer (timer) for general use, with output on a power relay.
At the base of the assembly is the well-known integrated circuit, with multifunctional timer functions, the generic called 555 (NE555, LM555, XR555, CA555, etc.).
7. Preamplifier - input trainer for frequency meters
One of the main parameters of a frequency meter is the sensitivity, ie the minimum level of signal required at the input for the frequency meter to work properly.
Another important parameter is the frequency band, which must be as large as possible. The present installation has a sensitivity of the order of 25mV in the frequency range 100Hz… 100MHz.
At the limits of the lower and upper frequency band the sensitivity is 40mV. The amplifier is made with the transistor BFR91A which provides high amplification over a wide frequency range.
8. Top 209/210 - TOPSwitch Family - Electronic MOS-FET switch with PWM control
The specialized electronic switches MOS-FET TOPSwitch series, referred to in this article in TOP209 and TOP210, are often found in TV switching power supplies, computing equipment, network adapters for charging batteries in portable equipment, etc.
He they replace the linear regulators, being of small dimensions and dissipating reduced power. They also replace many of the external components (sometimes bulky) related to a complex linear source, comparable in performance.
Basically, TOP209 / 210 is an electronic MOS-FET switch (in DIP8 or S08 capsule), with PWM control in the grid, from low power gates - CMOS (under 6mW), has its own integrated high frequency oscillator (100kHz) and various protections (thermal with hysteresis when exceeding 145 ° C, current limitation in pregnancy, self-restart, etc.).
The polarization of the starting circuit of the oscillator is done at high voltage, which makes it suitable for direct power supply from the AC network (after rectification and filtering) - range 85… 230Vac (max. 8W).
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