Desventajas
2.6. Descripción de las clases y las funcionalidades necesarias 1. Clases Controladoras
bhaskar banerjee
t
he fluid-level controller circuit pre- sented here allows you to set the lower and upper fluid levels at the desired specific positions between two extreme levels. The total fluid level is divided into ten equal parts. Any two of these ten positions may be defined as‘low’ and ‘high’ level, respectively. The system shows the preset levels on the two 7-segment displays and the current fluid level at any instant on a 10-LED bar graph indicator. The same circuit could also be used for controlling temperature in a similar fashion.
from ground level (0V) to supply voltage.
Thus the reference voltage source should be externally preset, which is feasible with the help of IC1. This IC can also display the input voltage on a linear scale using ten LEDs in the bar graph or the dot mode.
Here we have used the bar graph mode.
The outputs of IC1 are
active-‘low’ and hence they sink current to illuminate LEDs. Inverters are used between the outputs of IC1 and the inputs of IC3 and IC4 to invert the active-‘low’ outputs of IC1. There are ten outputs available from IC1,
the circuit
The main part of the circuit as shown in Fig. 1 is dot/bar graph driver LM3914 (IC1). This IC is linearly scaled and is intended for use in LED voltmeter appli-cation where the number of illuminated LEDs indicates the value of input voltage.
It contains a floating 1.2V reference source between pins 7 and 8 that may be used as the reference input for the IC. The voltage from the sensor is fed to the input of IC1 at pin 5.
The output of the sensor may vary
Fig. 1: Schematic diagram of fluid-level controller with indicator
of which only
possible to get more than ten outputs by cascading LM3941 ICs.)
Using this circuit, the maximum fluid level can be divided into four equal parts giving five different level readings from ‘0’ (empty/low level) to ‘4’ (full/high level). Thus the five levels are empty, one-fourth, half, three-level). Thus the five levels are empty, one-fourth, and full. This division is meant only for controlling the level, while all levels including the inter-mediate levels are constantly displayed on LED bar graph.
The lower level can be set anywhere between 0 and 3 in steps of 1 and high level can be set between 1 and 4. The fluid level can be maintained between any two levels by using IC3 and IC4.
IC3 selects the high level and gets inputs of levels 1, 2, 3, and 4, while IC4 selects the low level and gets inputs of levels 0,
1, 2, and 3. All
The required binary word is generated by a dual divide-by-16 counter IC6 (4520).
(IC6 can be replaced by a divide-by-10 counter 4518, if desired.) Half of IC6 is used for high level and the other half for low level. IC6 gets its counting pulse from a 555 timer (IC7) used for generation of approximately 1Hz pulse train.
The high level is set by pressing switch S1, while the low level is set by pressing switch S2. IC6 is reset when the power is
switched on. This power-on-reset function is realised using capacitors C1 and C2, and resistors R12 and R13. The part of IC6 connected to high-level selector also gets reset when the count is 5 (101 binary).
This reset pulse is generated using AND gates of IC CD4081.
The selected minimum and maximum levels are displayed by two 7-segment dis-plays DIS1 and DIS2 that are controlled by two BCD-to-7-segment decoders 4511 (IC9 and IC10, respectively).
The outputs of IC3 and IC4 are fed to the select input pins of IC5 (4051).
The output of IC5 is fed back to one of its select inputs through an inverter. IC5 determines the control logic. The pump (or the heater in temperature controller) should be ‘on’ when the fluid (or tempera-ture) level is below the minimum level and should remain ‘on’ until the maximum level is reached. It must not start if the fluid level falls below the maximum level
Fig. 4: Actual-size, single-sided PCB layout for fluid-level controller with indicator Parts List
IC6 - 4520 dual binary counter IC7 - 555 timer
IC8 - 4081 quad 2-input AND IC9, IC10 - 4511 BCD-to-7-segment gate
latch/decoder/driver R11-R15 - 10-kilo-ohm R32-R33 - 47-kilo-ohm R34 - 1-kilo-ohm VR1 - 10-kilo-ohm preset Capacitors:
C1, C2 - 22µF, 25V electrolytic C3, C4 - 10µF, 25V electrolytic C5 - 1µF ceramic disk Miscellaneous:
DIS1, DIS2 - Common-cathode 7-segment display S1, S2 - Push-to-on switch
Fig. 5: Component layout of PCB
transformer that is used to power the cir-cuit. Alternatively, a separate step-down transformer may be used for the purpose, but taking into account the voltage and current ratings of the lamp.
One may also use the sensor described in ‘Digital Water Level Meter’ in Circuit Ideas section of the February 2000 issue of EFY (also in Electronics Projects Vol. 21).
Use that sensor (VR4) as part of a voltage divider network as shown in Fig. 3. If the circuit is used as a temperature controller, a temperature sensor using the popular LM35 IC may be built (refer Circuit Ideas published in March 1993 issue of EFY or Electronics Projects Vol. 14).
Operation. The lower or the mini-mum level is set by pressing switch S2 and the upper or the maximum level by press-ing switch S1. The two switches should be kept pressed until the required level is displayed. For example, if the lower level is selected 1 and the upper level 3, the pump (or heater or a flow valve) will start when the fluid falls below level 1 and will stop when the fluid reaches level 3.
Assembly and testing. The circuit may be built on a veroboard. However, an actual-size, single-sided PCB and its component layout are shown in Figs 4 and 5, respectively. Switches used, should be of good quality. After assembling, the circuit may be tested using a voltage divider (po-tentiometer) that could be varied between ground and positive supply.
While testing, set preset VR1 to in-crease or dein-crease the reference voltage taking into account the maximum output available from the actual sensor. In case of power failure, there should be proper battery back-up. Otherwise, the system will not behave as desired. Red and green LEDs are arranged in alternate fashion to make the bar display look attractive. ❏ This function is realised by IC5 that can
operate a pump (or an alarm, or a flow valve, or a heater, as required) according to this control logic. For this, the input lines of IC5 are set to appropriate logic levels, which must not be disturbed.
Sensor. To control the fluid level (say,
water level in a tank), an optical sensor as shown in Fig. 2 may be used. This optical sensor consists of a small filament lamp (generally used in torch or an IR LED as light source) and an LDR or a photodiode as the sensor. The filament lamp may be powered using the same step-down Readers’ comments:
Q1. Please explain the detailed working of the circuit. Also elaborate as to how to arrange the LDR and filament lamp in the tank? Please give details, how water level will be controlled by LDR? Is there any reflection of light from water surface?
Ajit Through email a1. EFY: The optical sensor section (LDR and filament lamp) can be fixed rigidly on the bottom side of the tank lid/cover using M-seal or Fevi Quick or similar compound.
Alternatively, you may mount them on a wooden strip and secure the strip to the
bottom side of the tank cover. The work-ing of the LDR to control the water level is explained below.
The light rays from the lamp are re-flected from the water surface and fall on LDR1. The orientation and the intensity of light source are the deciding factors for incidence of adequate reflected light on the LDR for proper control of water level control.
No direct light should be allowed to fall on the LDR. Fix a suitable opaque screen closer to LDR, between the light source and the LDR.
For any given orientation of the light source and the position of the LDR, the
reflected light intensity received by the LDR will be low when the water level is low and it will increase as the water level in the tank rises. (The intensity at the LDR depends on the total length of the path travelled by light.) Thus the re-sistance of LDR is high when the level of water is low and its resistance decreases as the water level increases. The intensity of light is indicated by the LEDs and 7-segment display in Fig. 1. of the article.
VR2 (preset) is used to vary the sensitivity of LDR1 so as to obtain a predetermined LED/7-segment display when a specified level is reached.
MGMA—A MiGhty GAdGet with Multiple ApplicAtions
a. jeyabal
M
GMA, pronounced as migma, is a versatile and multi-purpose gadget. It can be used for a range of applications, from a simple toy to domestic and workbench applications.It measures time, compares light output, temperature, resistance and capacitance, etc. You can use this gadget in a number of ways, depending on your imagination and creativity.
Basically, MGMA is a resistance-capacitance-controlled oscillator that counts the pulses for a specific period. If any transducer, such as light-dependent resistor (LDR) or heat-dependent resis-tor (thermisresis-tor), is connected to it, the display shows the value corresponding to its resistance. Contact or break (normally open or closed) type transducers can also be used with MGMA.
tor C1, and potmeter VR1 form the oscillator circuit. Let us presume that capacitor C1 is in discharged state and pin 2 of gate N1 is in high state. As the input pin is low, output pin 3 is high and capacitor C1 starts charging through potmeter VR1.
When the voltage across capacitor C1 reaches above half of the supply voltage, input pin 1 of gate N1 goes high and output pin 3 goes low. Now capaci-Fig. 1 shows the block diagram of
the MGMA circuit. Block 1 is an oscil-lator that is controlled by block 2. Block 2 contains another oscillator whose fre-quency is much lower than that of the former. The differentiator circuit in block 3 resets the decade counters periodically.
Blocks 4 and 5 count the pulses, which, in turn, are displayed by blocks 6 and 7. Digit 9 in tens counter is decoded by block 8, and its output disables the counting process and triggers the aural indicator in block 9. Block 10 comprises the regulated power supply to run the gadget.
circuit
Oscillator. In Fig. 2, Schmitt trigger input NAND gate N1 of IC1 (CD4093),
capaci-Fig. 1: Block diagram of the MGMA circuit
Parts List Semiconductors:
IC1 - CD4093 quad 2-input Sch-mitt trigger NAND gate IC2, IC3 - CD4033 decade counter/
7-segment decoder IC4 - 7805 +5V regulator T1 - BC557 pnp transistor T2 - SL100 npn transistor D1-D7 - 1N4148 switching diode D8, D9 - 1N4001 rectifier diode LED1 - Red LED
Resistors (all ¼-watt, ±5% carbon, unless stated otherwise)
R1, R6-R9 - 100-kilo-ohm R2 - 220-kilo-ohm R3 - 470-kilo-ohm R4 - 3.3-kilo-ohm R5, R10, R11 - 330-ohm
VR1 - 1mega-ohm pot., linear VR2 - 47-kilo-ohm pot., linear Capacitors:
C1, C3 - 0.001µF ceramic disk C2 - 4.7µF, 10V tantalum C4 - 1000µF, 25V electrolytic C5, C6 - 0.1µF ceramic disk Miscellaneous:
X1 - 230V AC primary to 9-0-9V AC, 100mA secondary trans-former
S1, S2 - Push-to-on switch S3 - SPST switch, 230V AC DIS1, DIS2 - LT543 7-segment,
common-cathode type LED display SOC1 - SOC4 - Earphone socket SOC5 - DC IN socket PZ1 - Piezo-buzzer
- IC bases, knobs, mains chord, cabinet
- Banana-type earphone plugs
tor C1 discharges through potmeter VR1. When the voltage across capacitor C1 falls below half of the supply voltage, pin 1 of gate N1 goes low and the output pin goes high. Now capacitor C1 starts charging again and the cycle repeats itself.
The pulses from the output of gate N1 reach counter IC2 through resistor R1. Switch S1 is provided to stop the counting manually by grounding the
pulses through R1 when switch S1 is pressed.
Counter and display. The output of the oscillator is connected to clock input pin 1 of IC2 (CD4033, a decade counter for unit digits). The carry-out pin 5 of IC2 is connected to the clock input of decade counter IC3 that is meant for ten’s digits.
The segment outputs of both IC2 and IC3 go to the respective seven segments of DIS1 and DIS2 (LT543) for displaying
the number of pulses.
Lamp-test (LT) pin 14 of both IC2 and IC3 is grounded through 100-kilo-ohm resistor R8. The test-point (TP) may be used to check the display.
When a high-level voltage (5V) is applied to the test-point, all segment outputs go high and the display shows 88.
The display is blanked out when the number to be dis-played is 0, provided the ripple blanking input (RBI) pin