CAPÍTULO III: DESARROLLO DEL TRABAJO
3.4 Desarrollo del trabajo
3.4.2 Mejora de los procesos de pintado
equal to the reciprocal of its frequency, i.e. T = 1/f.
The above equation indicates that if one divides the angle described during one complete cycle of the sinewave (2π = 360o) into equal parts, then time period T of the wave will be divided into identical equal parts. Thus, it becomes fairly easy to set the different programmable timings synchronised with the ac mains sinewave at zero crossing. The main advantage of such an arrangement, as already men- tioned earlier, is that only the firing time has to be programmed to set different fir- ing angles. It is to be noted that the more precise the timer, the more precise will be the power being controlled.
In this circuit, the time period of mains waveform is divided into 20 equal parts. so, there is a time interval of 1 ms between two consecutive steps. The sam- pling voltage is unfiltered full-wave and is obtained from the diode bridge at the out- put of the power transformer. The timer is reset at every zero crossing of full wave and set again instantly for the next delay time. This arrangement helps the timer to be set for every half of mains wave—when the positive half of the mains waveform starts building up, the timer is set for that half and as it begins to cross zero, it gets reset and set again for negative half, when the negative half begins to build up. The process is repeated. Here, instead of using two zero crossing detectors—one for each half of mains wave—a single detector is used to perform both the functions. This is possible because the sampling wave for negative half is inverted by the rectifier
diode bridge.
The 18V ac from power trans- former is fed to the four diodes in bridge configuration, followed by the filter capacitor which is again followed by a three-terminal voltage regulator Ic lm7812. The voltage so obtained drives the circuit. The unfiltered volt- age is isolated from the filter capacitor by a diode and is fed to zener diode d8, which acts as a clipper to clip voltage above 6 volts.
This voltage is fed to the base of transistor T1, which is wired as zero crossing detector. When base voltage reaches the threshold, it conducts. It thus supplies a nar- row positive pulse which resets the timer at every zero crossing.
a 32.768kHz crystal is used to get stable output of nearly 1 kHz (1,024Hz) frequency after five stages of binary division by an oscillator-cum-divider Ic cd4060. The 32.768kHz crystal is used because it can be found in unused quartz clocks and is readily available in the market. but use of a 1kHz crystal using a quad-NaNd Ic cd4093 as clock generator, as shown in Fig. 2, is better as it provides the ex- act time interval required. In that case, cd4060 oscillator/divider is not required.
The cd4017b counter-cum-decoder Ic then divides this 1kHz signal into ten equal intervals, which are programmed via the single-pole, 10-way rotary switch. Once the delayed output reaches the desired time interval, the corresponding output of
cd4017 inhibits the counter cd4017 (via pole of rotary switch and diode D6) and fires the Triac. Transistor T2 here acts as a driver transistor. The reset pin of 4017 is connected to zero crossing detector out- put to reset it at every zero crossing. (The load-current waveforms for a few positions of the rotary switch, as observed at eFy Lab, are shown in Fig. 3.)
The circuit can be used as power control- ler in lighting equipment, hot-air oven, uni- versal single-phase ac motor, heater, etc.
luggAge SeCurity SyStem
dhuRjati sinha
W
hile travelling by a train or bus, we generally lock our luggage using a chain- and-lock arrangement. but, still we are under tension, apprehending that somebody may cut the chain and steal our luggage. Here is a simple circuit to alarm you whenselect 1 select 2 sound effect (pin6) (pin1) X X Police siren Vdd X Fire-engine siren Vss X Ambulance siren “-” Vdd machine-gun sound
Note: X = no connection; “-” = do not care
T
he add-on circuit presented here is useful for stereo systems. This circuit has provision for connecting stereo outputs from four different sources/ channels as inputs and only one of them is selected/ connected to the output at any one time.When power supply is turned ‘on’, channel a (ar and al) is selected. If no audio is present in channel a, the circuit waits for some time and then selects the next channel (channel b), This search operation continues until it detects audio signal in one of the channels. The inter- channel wait or delay time can be adjusted with the help of preset Vr1. If still longer time is needed, one may replace capacitor c1 with a capacitor of higher value.
suppose channel a is connected to
Add-on Stereo ChAnnel SeleCtor
Cum level indiCAtor
pRaBhash k.p.
a tape recorder and channel b is con- nected to a radio receiver. If initially channel a is selected, the audio from the tape recorder will be present at the output. after the tape is played com- pletely, or if there is sufficient pause between consecutive recordings, the circuit automatically switches over to the output from the radio receiver. To manually skip over from one (selected) active channel, simply push the skip switch (S1) momentarily once or more, until the desired channel inputs gets selected. The selected channel (a, b, c, or D) is indicated by the glowing of corre- sponding led (led11, led12, led13, or LeD14 respectively).
Ic cd4066 contains four analogue switches. These switches are connected
to four separate channels. For stereo op- eration, two similar cd4066 Ics are used as shown in the circuit. These analogue switches are controlled by Ic cd4017 outputs. cd4017 is a 10-bit ring counter Ic. since only one of its outputs is high at any instant, only one switch will be closed at a time. Ic cD4017 is configured as a 4-bit ring counter by connecting the fifth output Q4 (pin 10) to the reset pin. ca- pacitor c5 in conjunction with resistor r6 forms a power-on-reset circuit for Ic2, so that on initial switching ‘on’ of the power supply, output Q0 (pin 3) is always high’. The clock signal to cd4017 is provided by Ic1 (Ne555) which acts as an astable multivibrator when transistor T1 is in cut-off state.
Ic5 (KA2281) is used here for not it. When the wire (thin enameled copper
wire of 30 to 40 sWG, used for winding transformers) loop around the chain is broken by somebody, the base of transis- tor T1, which was earlier tied to positive rail, gets opened. as a result, transistor T1 gets forward biased to extend the positive
supply to the alarm circuit. In idle mode, the power consumption of the circuit is minimum and thus it can be used for hundreds of travel hours.
To enable generation of different alarm sounds, connections to pin 1 and 6 may be made as per the table.
only indicating the audio levels of the selected stereo channel, but also for for- ward biasing transistor T1. as soon as a specific threshold audio level is detected in a selected channel, pin 7 and/or pin 10 of Ic5 goes ‘low’. This low level is coupled to the base of transistor T1, through diode- resistor combination of d2-r1/d3-r22. as a result, transistor T1 conducts and
causes output of Ic1 to remain ‘low’ (disabled) as long as the selected channel output exceeds the preset audio threshold level.
Presets Vr2 and Vr3 have been included for adjustment of individual audio threshold levels of left and right stereo channels, as desired. Once the multivibrator action of Ic1 is disabled,
output of Ic2 does not change further. Hence, searching through the channels continues until it receives an audio signal exceeding the preset threshold value. The skip switch s1 is used to skip a channel even if audio is present in the selected channel. The number of channels can be easily extended up to ten, by using ad- ditional 4066 Ics.