Conex Club Magazine - no.2 - 2000

Conex Club Magazine - no.2 - 2000 - CMOS logic circuits

Reading time: 3 minute

The main topics presented

1. 75W amplifier

An audio amplifier, in monophonic structure, with high output current capacity can be made with the integrated circuit TDA1514. It is part of the Hi-Fi category, being present in most electronic blocks in radios, TVs or other audio installations.

Its technical characteristics also recommend it in equipment with digital sound processing (Compact Disc equipment).

Integrated circuit benefits from total electrical protection and Standby and Mute functions, activated by external components correctly mounted in the circuit. TDA1514 works with either a differential, symmetrical power supply or an asymmetric power supply.

The audio amplifier shown has the following technical characteristics:

• Output power (RMS) Po: 50W on a 4 Ohm load or 30W on an 8 Ohm load;
• Music output power: 75W on a 4 Ohm load or 45W on an 8 Ohm load;
• Input sensitivity: 285mV / 22 KOhm;
• Power supply: +/- 28V, maximum consumption 2A;
• It can be connected to the bridge with another amplifier of the same type: 100W / minimum 8 Ohm;

Bridge coupling mode the second amplifier with TDA1514 is provided in figure 3 (from the article); the power supply is made from a differential source symmetrical to the ground.

2. Automatic for rotation

The angular displacements of some directive antennas or of the image collectors impose a more accurate correlation between the operator and the execution element.

The machine presented in the article satisfies this independence and in addition is reliable at a low cost price.

Communications in VHF and UHF bands require the use of directional antennas with high gain type HB9CV, YAGI or F9FT.

As the radio connections established by amateur radio can be in any direction, this situation requires that the antenna has the radiation chimney oriented in that direction.

The situation is practically solved by mounting the antenna on a mechanical rotation system. This rotation system is composed of a motor that drives the speed reduction gears. Rotate the antenna to 360 degrees in about 30 seconds.

3. CMOS logic circuits

Digital integrated circuits CMOS (Complementary - Symetry Metal - Oxide - Semiconductor) were developed in the laboratories of the American company RCA.

The most famous logical family is series 4000, launched in 1968. As an alternative, National Semiconductor realized family 54C / 74C, the pin-to-pin equivalent of TTL logic circuits (logic integrated circuits made with bipolar transistors - Transistor - Transistor - Logic) from family 54/74.

Thus, design engineers accustomed to TTL circuits could extrapolate their experience to projects with the 54C / 74C circuit family.

A number of well-known manufacturers have tried, in order to meet the growing demand, to introduce CMOS circuits that perform more complex functions.

An example is the company Motorola which added to the 4000 series the 4500 series.

The main advantages of using CMOS circuits are: good noise immunity, low power consumption (a 100-port logic network consumes less than 1mW), wide range of supply voltage (3 - 20V), as well as the presence, in most models, of buffer stages on inputs and outputs (situation in which the output impedance in the ON state is independent of the internal structure of the logic gate)…

4. Motorola MC3362

This circuit is a complete receiver for narrowband frequency modulation (FM), with double frequency change, recommended in analog or digital radiocommunications, very suitable for amateur radio.

At the entrance it has a very good sensitivity, of approx 0.6uV. The first local oscillator uses a VCO in the PLL loop but also admits a quartz.

The first intermediate frequency is usually 10.7MHz which mixed with 10.245MHz produces 755kHz which is demodulated. The mixers in the circuit have a gain between 18 and 22dB.

The circuit is recommended for the maximum input frequency of 200MHz. The supply is made with voltage between 2 and 6V.

5. Car alarm

Theft of a car, the presence of an instructor in our own habitat, floods or the start of a fire are tragic situations.

There are various solutions, more or less efficient, that allow avoiding these phenomena with sometimes catastrophic consequences, but the cost price is often prohibitive.

Regarding the endowment of the personal car with a warning system, it is proposed to create a simple and easy to do module, with a minimum of components.

The statements are completely covered if we take into account that the assembly is done with one Schmitt Trigger NAND logic gate integrated circuit (CD4093), three low power transistors, a relay and some passive components.

It performs the important and necessary functions of a quality warning: timed triggering and arming or immediate triggering.

The technical data of the alarm are:

  • Timed entry: 4… 8s;
  • Immediate entry;
  • Reinforcement time: 20… 40s;
  • Alarm time: 40… 60s;
  • NI / ND relay type output: 6A / 250V;
  • Power supply: 12V, 10mA consumption in standby mode.

5. Voltage reference

For the calibration of the measuring devices, it is recommended to make the voltage reference presented in figure 1 (from the article) and made with MAX873A integrated circuit (B).

The calibration voltage supplied at the output (+ Ref) is 2.5V with 0.1% accuracy; adjustment between limits 2.495V and 2.505V is made from P1.

The temperature stability coefficient is good, the thermal drift being 20ppm / 1000 hours. The assembly is powered by 9V.

Disconnect capacitors are indispensable, having the role of minimizing the sources of fog. The consumption is 10mA, and the integrated circuit is short-circuit protected on the output.


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