Numeric Water Level Indicator_www.projectspedia 715h41

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Numeric Water Level Indicator With Display OVERVIEW Most water level indicators are equipped to indicate and detect only a single level. The Numeric Water Level Indicator implemented here can indicate up to nine such levels and displays the level no. on a seven segment display. Hence, not only is the circuit capable of cautioning a person that the water tank has been filled up to a particular level,

Fig. 1: Block diagram of the Numeric Water Level Indicator with Display

it can also indicate that the water level has fallen below the minimum level. This circuit exploits the simple fact that water is a good conductor of electricity. The placement of nine probes (having connections to the circuit) at different heights inside the water tank determines the nine different detectable levels. When the water reaches a particular height in the tank; the seven segment display shows the corresponding level no., digit ‘9’ representing the “tank full” condition and digit ‘0’ representing the “tank empty” condition.

Table1

Truth Table for the Priority Encoder 74HC147

in the tank through its nine input terminals (which are ‘active low’ inputs). These inputs are further converted to ‘active low’ BCD output. These are inverted by the four NPN transistors and then fed to the input pins of the latch decoder driver IC CD4511. BCD to 7-segment latch decoder drivers CD4511: The CD4511 is a BCD to seven segment latch decoder and driver. The circuit provides the functions of a 4-bit storage latch, an 8421 BCD-to-seven segment decoder, and an output drive capability. It has a total of 4 inputs namely A, B, C and D.

COMPONENT DESCRIPTION 10 to 4 Line Priority Encoders 74HC147: The 74HC147 priority encoder accepts data from nine active LOW inputs (A0 to A8) and provides a binary representation on the four active LOW outputs (Y0 to Y3). A priority is assigned to each input so that when two or more inputs are simultaneously active, the input with the highest priority is represented on the output, with the input line A8 having the highest priority. The device features 10-line to 4line priority encoding function by use of the implied decimal “zero”. The “zero” is encoded when all nine data inputs are HIGH, forcing all four outputs HIGH. All inputs are equipped with protection circuits against static discharge and transient excess voltage. In the Numeric Water Level Indicator circuit, this priority Fig. 2: Pin out of the encoder IC senses the water level 74HC147 Priority Encoder IC

Table- 2

Truth table for the BCD to seven segment latch decoder drivers CD4511

Fig. 3: Pin-Out of the CD4511 IC

NPN transistor BC547: The BC547 is a general purpose transistor used for switching and amplification purposes. In the Numeric Water Level Indicator circuitry, these transistors are being basically used as © Kits‘n’Spares

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Resistors (R1-R24)

Printed Circuit Board (PCB)

IC Sockets

Fig. 4: Pin Configuration of a BC547

Common Cathode 7-Segment LED Display LTS 547AP: The LTS 547AP is a general-purpose seven segment LED Display. The Numeric Water Level Indicator uses this display to show the number associated with the water level in the tank. If water is at level 1 in the tank, the segments B and C light up to indicate this. Similarly for level 2, the segments A, B, Fig. 6: Segments of G, E, D light up and so forth. the common-cathode LTS543

Resistors: The most basic role of resistors is current limiting i.e. precisely controlling the quantity of electrical current that is going to flow through a device or a conductor. Resistors can also be used as voltage divider, in other words they can be used to generate any voltage from an initial bigger voltage by dividing it. They are also used as pull-up resistors in electronic logic circuits to ensure that inputs to logic systems settle at expected logic levels if external devices are disconnected or high-impedance. They may also be used at the interface between two different types of logic devices, possibly operating at different power supply voltages.

Display (DIS1)

Priority Encoder (IC1)

Fig. 5: Connection of a NPN Transistor to Implement NOT Gate Logic

inverters i.e. to implement the NOT gate logic. Inverters (NOT gates) are available on logic ICs but since only one logic inversion is required at each of the four outputs of the priority encoder, the simple arrangement shown in fig5 can be used. With these connections, the following inputoutput sequence is achieved: • When the input is high (+Vs) the output is low (0V) • When the input is low (0V) the output is high (+Vs).

Decoder Drivers (IC2)

NPN Transistors (T1 to T4) Component Identification

Level Probes (L1to L9)

Display (showing digit ‘9’)

Connections to +5V DC

Completed prototype after assembling the components and soldering (indicating “tank full”)

Level Probes (L1to L9)

Display (showing digit ‘0’)

Connections to +5V DC

WORKING PRINCIPLE

Completed prototype after assembling the components and soldering (indicating “tank empty”)

The Numeric Water Level Indicator employs a simple mechanism to detect and indicate the water level in a tank or any other container. The level sensing is done by a set of nine probes which are placed at nine different levels on the tank walls (with probe9 to probe1 placed in decreasing or-

der of height; COM probe is placed on the base of the tank). Basically, level9 represents the “tank full” condition while COM represents the “tank empty” condition. When the tank is empty, all the inputs to the priority © Kits‘n’Spares

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Fig. 7: Circuit Diagram of the Numeric Water Level Indicator with Display

encoder 74HC147 (IC1) remain high, as 2. Transistor Parts List 3. IC Sockets a result its output also remains high. Semiconductors: 4. Seven Segment Display Since these outputs are inverted and fed IC1 - Priority Encoder IC • Hold the soldering iron like a as inputs to the decoder driver CD4511 74HC147 IC2 - BCD to Seven Segment (IC2), all inputs to IC2 are low. The pen, near the base of the handle. Touch Decoder IC CD4511 seven segment display correspondingly the soldering iron onto the t to be T1 to T4 - NPN Transistor BC547 shows a ‘0’, indicating that the tank is made. Make sure it touches both the Resistors (all ¼-watt, ±5% carbon): empty. component lead and the track. R1 to R9 - 560 kilo-ohm R10 to R13 - 12 kilo-ohm • Hold the tip there for a few For example, when the water reaches R14 to R17 - 33 kilo-ohm level1 (but is below level2), pin11 (A0) seconds and feed a little solder onto the R18 to R24 - 470 ohm of IC1 is pulled to ground and the outt. It should flow smoothly onto the Miscellaneous: put generated at pin9 (Y0) of IC1 also lead and track to form a volcano shape. DIS1 - Common Cathode Seven becomes low. After inversion, the bits Apply the solder to the t, not the Segment Display fed to the input pins of IC2 are 0001 (LTS543) iron. Printed Circuit Board (PCB) • Remove the solder, then the (DCBA). Hence, the corresponding digit displayed by the seven segment display iron, while keeping the t still. • After all the components have been soldered, check is a ‘1’. The same mechanism applies to the detection of all the other levels. the soldering closely for any breaks. Inspect your work careWhen the tank is full, all inputs to IC1 become low and fully under a bright light. The solder ts should have all its outputs also go low. This causes all the inputs to IC2 a ‘shiny’ look about them. Check that there are no solder to go high and hence the display shows a ‘9’, thereby indibridges between adjacent pads. Connectivity in circuit can cating a “tank full” condition. be tested by the help of a multi-meter

ASSEMBLING THE KIT Preparing the soldering iron: • Place the soldering iron in its stand and plug in. The iron will take a few minutes to reach its operating temperature of about 400°C. • Dampen the sponge in the stand. • Wait a few minutes for the soldering iron to warm up. You can check if it is ready by trying to melt a little solder on the tip. • Wipe the tip of the iron on the damp sponge. This will clean the tip. Melt a little solder on the tip of the iron. Soldering the components: • Use the component overlay on the PCB to insert the components and solder them in the following order: 1. Resistors

Precautions to be taken: • Please note the connection of jumper wires on the PCB. These are denoted on the PCB with the letter “J” along straight lines indicating the drills where they are to be soldered. • It is preferable to use multi-thread wires as jumpers rather than single thread copper wires since they tend to break upon soldering. • The pins of the IC sockets and the seven-segment display may have to be adjusted and bent in order to insert them into the drill-holes prior to soldering. (The sockets and not the ICs are soldered on the PCB, this is to make the mounting and dismounting of the ICs easy while testing and trouble-shooting) • The three-legged transistor should be carefully © Kits‘n’Spares

do-it-yourself placed into the correct drill holes on the PCB.

PRE-TEST Do not insert any ICs into their sockets yet. First, check the power supply to be applied and its polarity with a multi-meter before connecting it. Next, connect this requisite +5V DC supply and measure the voltage across pin 16 (+V cc) and pin 8 (GND) of IC1 and IC2. It should read approximately 5 volts. If this reading is ok then remove power and insert the ICs. Take care to not to bend any of the IC pins while doing so. Accidentally applying a larger voltage to the circuit can burn the IC’s or some other sensitive component on it.

TESTING • Now apply the supply voltage of +5V to the circuit again. • To perform a test on the level indication mechanism, place the probes on the walls of the tank (at 9 discrete levels) in the manner described earlier. After this placement, note the display when the tank is empty. It should show the digit ‘0’. • Next, fill the tank/container with water so as that the water level is above or at probe1. In this case, the display should show the digit ‘1’. Perform this test for each of the 9 levels. When the tank is full, the display should show the digit ‘9’ to represent this.

TROUBLESHOOTING If the circuit is not working as desired then proceed as below: • It is preferable to begin trouble-shooting process from output stage onwards and then proceed to the input side. To begin, apply a high to pin7 (input A) of IC2, while keeping the other three inputs low. In this case, the display

should show a ‘1’. • Check the display for each of the other nine conditions (i.e. display of digits 0, 2, 3, 4, 5, 6, 7, 8, 9) represented in Table2. If all these are displayed correctly for the corresponding input then the circuit stages beyond IC2 are working fine. Proceed with the next step. • Check the connections of the base, emitter and collector of the transistors and whether all the resistances being used are of the required value. that you have the right components in the right place. • Remove the IC from the IC socket and check that no IC pins are bent up under the body of the ICs. This can sometimes happen when inserting ICs into sockets. Check for voltages at characteristic socket-pins. The voltage between pin16 and pin 8 of IC1 and IC2 should be approximately +5V. Other characteristic values can be checked for by referring to the datasheets. If the ICs appear to have heated then replace them. Once the circuit problem has been resolved your Numeric Water Level Indicator is ready to be installed and used.

TRY THIS OUT NEXT! During summer months, the problem of over-flow while filling desert coolers is common. The water-level indicator described here can be implemented to overcome this problem. Each time the desert cooler has been filled to the brim i.e. level 9, the level indicator will display the digit 9 on the 7-segment display thereby checking the wastage of water!

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