Conex Club Magazine - no.4 - 1999

Conex Club Magazine - no. 4 - 1999 - Electronic tachometer

Reading time: 5 minute

The main topics discussed

1. The paper disk

When in the United States the first information on the actual data storage times began to appear in the press, it seemed that we would witness a great scandal.

As can be seen from the graph presented in the article, extracted from US News 02/16/98, the most common recording media, are far from our illusions in this field.

The most shocking situation is in the case of the CD. When it appeared, the majority of music and computer fans already believed they were in possession of the miraculous perfect recording solution, that is, unalterable over time.

Referring to the lifetime of the CD the word "infinite" is often pronounced, so that now we are "down to earth": a CD recording is comparable in storage time to a magnetic recording, thus disappearing one of the much trumpeted advantages of the CD technique.

Of course, the CD manufacturers have taken all measures to appease the spirits, any scandal in this field means the loss of astronomical sums...

Leaving aside the aspects related to the consumer market, let's see what problems these reduced safe storage times involve in the professional field, because here the problem of storage time is very serious.

It's about archive storage, of the elements of culture and art, in general, of everything that mankind has created and learned.

In this sense, the case of magnetic (digital) recordings of signals from Wiking space probe, transmitted in 1976 from Mars.

During a check made a few years ago, not even 20 years after the registration, it was found that about 10-20% of the information disappeared (irretrievably)..

Faced with this big problem, everyone (and here I am referring to the professionals in the field) is looking for and finding better or worse solutions...

2. Audio equalizer

Audio equalizers are assemblies that are interposed between the signal source and the power amplifier acting on some frequencies in the audio spectrum to attenuate or emphasize them.

A mono audio equalizer is presented, with 7 lanes made with the specialized integrated circuit (for correcting the frequency characteristic of signals from an electroacoustic chain) LA3607.

The technical data of the assembly are:

  • central frequencies: 60, 150, 400, 1000, 2500, 6000 and 15000Hz;
  • adjustment effectiveness: +/- 12dB;
  • input signal level: 250mVef / 20 kOhm for THD = 0.02% at the output;
  • output impedance: 1 kOhm;
  • supply voltage: 12V;
  • consumption: 10mA.

3. Car amplifier – 2 x 22W

The presented power amplifier can be made on the same wiring with three types of integrated circuits produced by Philips: TDA1552Q, TDA1553Q and TDA1557Q.

The basic electrical diagram of the assembly is presented in the article. It ensures a maximum musical power of 22W per channel on a load of 4 Ohm, being intended especially for use in cars. The main technical data of the amplifier are provided in the table in the article.

The input sensitivity is of 40mV for assembly with the integrated circuit TDA1557Qor 400mV for assemblies made with TDA1552Q and TDA1553Q.

The supply is made with a voltage within the range 12 - 18V. In no case will the value of 18V be exceeded because the integrated circuit will fail.

These integrated circuits have the output stages configured in the bridge, which allows the development of a high power on the load under the conditions of feeding from a car battery.

4. Electronic tachometer

Manufacturers of heat engines give as the main characteristic, for good operation, its speed. In order to use the engine correctly, for it to develop the required power but also to reduce fuel consumption, it is recommended to determine the exact speed of rotation of the crankshaft with an electronic tachometer, because it ensures a good measurement precision and a display of easily visible value.

The presented tachometer is made with the integrated circuit LM2917N (M) produced by National Semiconductor. This circuit is a frequency-voltage converter being very useful for electrical measurement applications, such as: speed measurement - turometer, capacity measurement - capacitor, indicator and/or latch exceeding the speed or frequency limit and many other applications.

5. Broadcast mixer

In issue 3 of the magazine, a VCO type oscillator was presented, in a PLL loop, with a step between channels of 12.5 kHz, for working with amateur radio repeaters or in monofrequency mode.

This oscillator offers signals in the frequency difference of 134.3 - 135.3 MHz. To be able to work in broadcasting, this signal must be mixed with a second signal with a frequency of 10.7 MHz, modulated in frequency.

Frequency deviation (at maximum modulation) must be of +/- 3kHz. Thus, at the output of the mixer, we will obtain 80 transmission or reception channels offset by 12.5kHz in the 145-146 MHz band.

6. Malfunctions of the low-level signal processing stages

In a classic analog TV receiver, the stages that process TV signals - low-level image, are the channel selector (tuner), the common-path IF amplifier and the video demodulator.

In the receiver NEI TV (Indiana 200), these functional floors are materialized through the channel selector TFK2000 KHC, the integrated circuit IC100 (TDA8305A) and their annex circuits.

During normal operation, the voltages at the terminals of the tuner and the integrated circuit are given in tables 1, 2 and 3 (from the article).

FAULTS from this area of ​​the receptor is manifested by specific symptoms, the most common of which are:

  • Lack of image and sound or noisy screen;
  • Channels from certain bands cannot be received;
  • Very noisy signal;
  • Unstable image (on lines and frames) at high signal or break on the image;
  • Unstable tuning or not keeping tuning on the channel.

7. Automatic for lighting

The automatic device presented in the article is particularly useful for public lighting, courtyards, shops or hallways.

The lighting fixtures are ordered automatically depending on the lighting of the environment in which the transducer is placed, in this installation a photoresistor.

The main technical characteristics of the assembly are:

  • supply voltage: 220V, directly from the mains;
  • load connected by electromagnetic relay;
  • maximum ordered load: lkW;
  • adjustable sensitivity.

8. FM transmitter – 88 – 108 MHz

The specialized literature (but especially the magazines intended for those who have as a hobby electronic assemblies of all kinds) is full of schemes for mini and micro transmitters.

The proposed assembly was designed and practically made by the author in order to obtain performances that exceed those of a commonplace "wireless microphone" produced many times as a toy for the amusement of children. Assembly is simple enough to be done even by novice builders.

Because, they have a "horror" of making and adjusting the coils, this time the coil is made directly on the printed wiring (in the form of a rectangular loop), which leads to the disappearance of the problem of "pulling into the lane".

The frequency on which the mini transmitter works is 88 - 108MHz, so the UKW band must also be excluded from any broadcasting station that could be jammed.

The range of the device does not exceed 100m and it cannot cause interference with various stations except for your close neighbors, but an elementary rule of ethics must make you refrain from such a thing (perhaps only for April 1st jokes!).

Another important feature of the mini-emitter is that the voltage on the double varicap diode (type BB204) is stabilized with the IC2 integrated circuit (type 78L05 in the plastic capsule), which does not allow the "escape" of the central frequency on which it will be tuned, only in very small limits.

9. Dynamic light

Light effects have always attracted people's interest because they are carriers of information about events that come out of the unknown.

Whether they are simple random appearances or repeated according to well-established laws, the light effects, as fun, attract a large number of participants.

It is almost unthinkable that a big concert in the hall or in the open air would not be accompanied by light effects that complement the acoustic sensation with the visual sensation in this way. Is there still a Christmas tree somewhere without the multicolored lights actively participating in the children's joy?

The assembly presented is a dynamic light with 8 channels made with two logical integrated circuits 74HC00or 74HC164.


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