T
he audio level indicator described here is quite simple and utilises readily available Ics. The functionof the circuit can be understood with refer- ence to Fig. 2 which shows two concentric circles formed by red and green leds
respectively.
When the audio level increases, the speed of the roulette (moving light effect
in the circles) also increases. The lighting leds of one of the two circles would ap- pear to move in clockwise direction, while
although the leds here are arranged in circular form and only two colours are used, a number of different combinations are pos- sible. For example, one may have red and green leds arranged in two rows, one over the other. leds of one row may be made to appear moving from left to right and of the other in the opposite direction, i.e from right to left.
In the circuit shown in Fig. 1, Ic 555 is wired to operate in an astable mode as a voltage con- trolled oscillator (VcO). The only difference here is that pin 5 (which is a frequency con- trolling pin connected to the inverting
es the internal flip-flop of timer Ne555 to set and re- set according to the audio level, and hence the output frequency varies corre- spondingly. This output is fed to the clock input pin of ring counter Ic cd4017 whose output advances at a rate proportional to the clock input or the audio level present at pin 5 of Ic2.
The audio output is not taken directly from the output of the deck (across speaker termi- nals) because the output across speaker termi- nals depends upon the setting of the volume control and would vary from one model to the other. Here, the left and the right outputs (in case of a stereo deck) are fed to the input of an audio amplifier Ic Tba810, via capacitors c1 and c2 (0.01µF). These low- value capacitors help to maintain the re- quired separation between left and right channels. Otherwise, at high frequencies the separation may fall tremendously, thereby short-circuiting l and r channels.
The 10k preset Vr1 before Ic Tba810 is used to control the output level so that at maximum output the potential at pin 5 of 555 is such that the frequency of 555 is between 1 and 15 Hz (approximately). Otherwise, all the leds at the output of Ic3 will appear flickering.
The other 10k preset Vr2 is used to set the normal speed of the roulette, be- tween 2 and 3 Hz. One point to be noted here is, that the audio signals should be taken from the output of preamplifier Ic of the deck just before the volume control. The output will depend on the setting of volume control (which we do not want) if it is taken after the volume control.
The power supply for the circuit may be tapped from the power supply of the deck, as shown in Fig. 1. The power sup-
Clever rAin-AlArm
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sually rain-alarms employ a single sensor. a serious drawback of this type of sensor is that even if a single drop of water falls on the sen- sor, the alarm would sound. There is a probability that the alarm may be false. To overcome this drawback, here we make use of four sensors, each placed well away from the other at suitable spots on the roof. The rain alarm would sound only if all the four sensors get wet. This reduces the probability of false alarm to a very great extent.The four rain-sensors sr1 to sr4,
along with pull-up resistors r1 to r4 (connected to positive rails) and inverters N1 to N4, form the rain-sensor-monitor stage. The sensor wires are brought to the Pcb input points e1 to e5 using a 5-core cable. The four outputs of schmitt inverter gates N1 to N4 go to the four inputs of schmitt
NaNd gate N7, that makes the alarm driver stage.
When all four sensors sense the rain, all four inputs to gates N1 through N4 go low and their outputs go high. Thus all four inputs to NaNd gate N7 also go high and its output at pin 6 goes to logic 0. The output of gate N7 is high if any one or more of the rain-sensor plates sr1 through sr4 remain dry. The output of gate N7 is coupled to inverter gates N5 and N6. The output from gate N5 (logic 1 when rain is sensed) is brought to ‘eXT’ output connector, which may be used to
control other external devices. The output from the other inverter gate N6 is used as enable input for NaNd gate N8, which is\ configured as a low- frequency oscillator to drive/modulate the piezo buzzer via transistor T1. The frequency of the oscillator/modulator stage is variable between 10 Hz and 200 Hz with the help of preset Vr1. The buzzer is of piezo-electric type having a continuous tone that is inter- rupted by the low-frequency output of N8. The buzzer will sound whenever rain is sensed (by all four sensors).
6V power supply (100mA) is used here to enable proper interfacing of the cmOs and TTl Ics used in the circuit. The power supply requirement is quite low and a 6-volt battery pack can be easily used. during quiscent-state, only a negligible current is consumed by the circuit. even during active state, not more than 20ma current is needed for driving a good-quality piezo-buzzer. Please note that Ic2, being of TTl type, needs a 5V regulated supply. Therefore zener d1, along with capaci- tor c2 and resistor r5, are used for this purpose.
a parallel-track, general-purpose Pcb or a veroboard is enough to hold all the components. The rain-sensors sr1 to sr4 can be fabricated as shown in the construction guide in Fig. 2. They can be made simply by connecting alternate parallel tracks using jumpers on the component side. Use some epoxy cement on and around the wire joints at a and b to avoid corrosion. also, the sensors can be cemented in place with epoxy cement.
If the number of sensors is to be in- creased, just add another set of cd40106 and 7413 Ics along with the associated discrete components. another good utility of the rain-alarm is in agriculture. When drip-irriga- tion is employed, fix the four sensors at four corners of the tree-pits, at a suitable height from the ground. Then, as soon as the water rises to the sen- sor’s level, the circuit can be