Parmar Latesh B.
M
any circuits of water-level con- troller have appeared in EFY.What sets this circuit apart from all of them is that it shows the level of wa-ter far away from the location of the over-head tank. Its other features include:
1. Up to five levels of water are in-dicated on LED display along with beep sound.
2. DTMF receiver section controls the on/off function of the motor.
3. No battery is required to store the water level when power fails.
4. The water-level scanning section scans the water level with beep sound after power resumes.
5. When water reaches the full level, the motor turns off and provides a beep sound for about a minute.
6. When water goes below the empty level, the motor starts with beep sound.
Fig. 1 shows the remote water-level sensing and DTMF transmitter circuit.
At the heart of the circuit is NAND gate CD4093 with resistor-capacitor combina-tion and diode network that senses the water level in the overhead tank. Water inside the tank is divided into five levels, namely, Empty, 1/4th, Half, 3/4th and Full. The DTMF codes used to indicate Empty, 1/4th, Half, 3/4th and Full levels are 1, 2, 3, 4 and 5, respectively. Different levels are indicated by different colour LEDs at the DTMF receiver end.
Suppose water level goes below Empty mark. Transistor T1 stops conducting and the output of NAND gate N1 goes low through resistor R1, capacitor C1 and diode D1. At the same time, the scanning output of NAND gate N12 also goes low.
So trigger pin 6 of dual-timer NE556 (IC5), which is wired as a monostable, goes low to drive its output pin 5 high. As a result, column C1 and row R1 of DTMF dialler UM91214B (IC 10) short through analogue switch CD4066 (IC8) and dial the number
corresponding to the Empty level. The DTMF output at pin 7 of IC10 is transmit-ted through wire link to the receiver (Fig.
2). The output of dialer is connected to DTMF decoder CM8870 (IC13) to decode the received signal. The decoded output sets flip-flop CD4013 (IC15) through BCD to decimal decoder IC14 to switch on the motor with LED indication and beep sound.
As water goes up and touches differ-ent level-sensing probes, NAND gates N1, N3, N5, N7 and N9 go low one by one and the corresponding differentiator networks activate to trigger IC5 through IC7, re-spectively, to produce a high output and transmit the corresponding DTMF code by dialer IC10. DTMF codes are transmitted one by one as the water level goes up and touches the different sensing probes. The sensor probes should be made of stainless steel to avoid corrosion.
Timers IC5 through IC7 are wired in monostable mode. The output of the monostable goes high for about 2.4 seconds when its trigger pin goes low.
As water is consumed, its level in the tank falls below different sensor probes and the outputs of NAND gates N2, N4, N6, N8 and N10, with resistor-capacitor combination and diode network, go low one by one. This low output is applied to the trigger pin of dual-timer IC5 through IC7 and the DTMF code corresponding to the level is generated by IC10. The output of the corresponding toggle flip-flop in the receiver section goes low to turn off the related LED, which indicates that water level is below that particular level.
The main purpose behind adding the level-scanning section is to avoid mal-functioning of the receiver section due to power failure (as no battery is added to the receiver to latch the present level of the water). In case we add a battery and the power fails, the water level is latched
February
but during this period if the water level goes below any probe, there is no way to transmit the signal from the transmitter.
This leaves us with no other option but to add the level-scanning section.
When power resumes, the level-scan-ning section scans and checks all the levels one by one (from Empty to Full) and transmits the corresponding codes to the receiver to show the water level in the overhead tank. So when the power resumes, the output of NAND gate N11 goes low after a delay of about 7 seconds, which is set by the combination of resistor R36 and capacitor C27, and trigger pin 6 of dual-timer IC11 goes low.
One timer of IC11 is used as a monos-table whose output pin 5 remains high for about 23 seconds. Since pin 5 is directly connected to reset (pin 10) of the other timer of IC11, it is also activated for 23 seconds to generate the pulse. The second timer of IC11 is wired as an astable mul-tivibrator to generate 1-second ‘on’ time and 3-second ‘off’ time signals at its pin 9.
The 1-second pulse is fed to clock pin 14 of CD4017 (IC12), which scans one of the two inputs of NAND gates N12 through N16 each one by one. The other inputs of these NAND gates are connected to the cathodes of diodes D1 through D5 from the corresponding water level. The outputs of NAND gates N12 through N16 are con-nected, via diodes D19 through D23 and related resistor-capacitor networks, to the cathodes of diodes D6 through D10, respectively. As a result, trigger pins of IC5 through IC7 go low one by one and the outputs of corresponding timer sections go high, which shorts the related columns and rows of DTMF tone generator IC10 through analogue switch CD4066.
Fig. 2 shows the details of receiver and level indicator circuit. In the receiver sec-tion DTMF decoder CM8870 (IC13) is used to decode the received tone signal. This
Fig. 1: Remote water level sensing and DTMF transmitter circuit
Fig. 2: Receiver and level indicator circuit
IC converts the received DTMF code into equivalent binary form. BCD-to-decimal decoder CD4028B (IC14) converts this binary code into decimal. Its Q1 through Q5 outputs are connected to ‘D’ flip-flop CD4013 to control the motor and indicate water level in the overhead tank through the LED. The present water level in the tank is indicated by glowing of the respective LED. When the LED goes off, it means water in the tank is below the indicated level.
Initially, when the power is switched on or the power resumes, all flip-flops of CD4013B (IC15 and IC16), except one (whose reset pin 4 is connected to pin 6 of IC14), are reset through the resistor-capacitor network at pins 4 and 10 of the two ICs. Pins 1 and 2 of IC15 are con-nected to pin 6 of IC17 via capacitor C59 and the base of transistor T2 via capacitor C46, respectively, to control the motor.
The remaining flip-flop of IC15 is wired in set/reset mode.
When water goes below the Empty level, the set input of IC15 (as per the received signal) goes high to make outputs Q1 and Q1 high and low, respectively. The high Q1 output of IC15 energises relay RL1 and the motor is switched on auto-matically with the help of IC17 and tran-sistors T3 and T4; the motor is connected through the contacts of relay RL1.
For manually switching on the motor, press switch S1.
When water level touches the ‘Full’
probe, the reset input (as per the received signal) of IC15 goes high to make Q1 and Q1 outputs low and high, respectively. The high Q1 output of IC15 de-energises relay RL1 and the motor turns off automati-cally with the help of IC17 and transistors T3 and T4. You can also manually switch off the motor by pressing switch S2.
The motor-off state is indicated by a one-minute beep sound. NE555 (IC17) is
wired as a bistable multivibrator. When pin 2 of IC17 goes low, its output goes high to drive transistor T3 and transistor T4 de-energises relay RL1. When pin 6 of IC17 gets a high pulse, its output goes low and transistor T3 doesn’t conduct while transistor T4 conducts to energise relay RL1. The motor on/off (for empty/full tank) is indicated by the respective LED.
The beeper section generates beep each time the LED indicates a new water level. At the output of flip-flop CD4013B, points Q, R, S, T and U for Empty, 1/4th, Half, 3/4th and Full level indications are connected to capacitors C50 through C53 and R67 at the base of transistor T8, respectively.
When the new water level is latched, the corresponding output of the flip-flop goes high and the LED lights up. At the same time, a small spike is passed to satu-rate transistor T5 to trigger pin 2 of mon-ostable IC18. The output of monmon-ostable goes high for about 500 ms, which is con-nected (through transistor T6) to NAND gate N17 to activate the NAND gate oscil-lator. IC20 is wired as an osciloscil-lator.
When the tank is full, pin 2 of IC15 goes high to trigger IC19 through tran-sistor T8. IC19 is wired as a one-minute monostable and transistor T7 activates the oscillator during this period. One-minute beep indicates that the tank is full and the motor has turned off.
The power supply circuit is shown in Fig. 3. The AC mains supply is stepped down by transformer X1 to deliver a secondary output of 7.5V-0-7.5V AC (15V AC), 1A. The output of the transformer is rectified by a full-wave bridge recti-fier comprising diodes D25 through D28.
Capacitor C60 acts as a filter to eliminate ripples. IC12 and IC22 provide regulated terminated on connector Con-1(A). These are to be extended to corresponding points of connector Con-1(B). Pads have been Fig. 3: Power supply
Parts List Semiconductors:
IC1-IC4, IC20 - CD4093 quad NAND gate IC5, IC6, IC11 - NE556 dual timer IC7, IC17-IC19 - NE555 timer
IC8, IC9 - CD4066 quad analogue switch
IC10 - UM91214B DTMF tone
generator
IC12 - CD4017 decade counter IC13 - CM8870 DTMF decoder IC14 - CD4028 BCD-to-decimal
decoder
IC15, IC16 - CD4013 dual D-type flip-flop IC21 - 7812 12V regulator IC22 - 7806 6V regulator T1, T6, T7 - BC548 npn transistor T2, T3, T8 - BC547 npn transistor T4 - 2N3019 npn transistor D1-D5,
D24-D28 - 1N4007 rectifier diode D6-D23 - 1N4148 switching diode ZD1 - 3.3V, 0.5W zener diode
Resistors (all ¼-watt, ±5% carbon, unless stated otherwise):
C1-C5 - 10µF, 25V electrolytic C6-C15, C28,
C34-C41, C44, C45, C50-C53,
C61-C66 - 0.1µF ceramic disk C16-C20, C49 - 4.7µF, 25V electrolytic C21-C25, C31,
C32, C47, C48,
C56 - 0.01µF ceramic disk C26, C27, C55 - 100µF, 25V electrolytic C29, C30, C46 - 47µF, 25V electrolytic C33, C42, C43 - 1µF, 25V electrolytic C54, C58, C59 - 0.22µF ceramic disk C57 - 0.47µF ceramic disk C60 - 1000µF, 25V electrolytic Miscellaneous:
X1 - 230V AC primary to 7.5V-0-7.5V, 1A secondary trans-former
XTAL1, XTAL2 - 3.578MHz crystal RL1 - 6V, 1C/O relay
PZ1 - Piezobuzzer
S1, S2 - Push-to-on switch
Fig. 5: Component layout for PCB-1
Fig. 4: Actual-size, single-side PCB for circuits of Figs 1 and 3 (PCB-1)
Fig. 7: Component layout for PCB-2
Readers’ comments:
Q1. IC6 (NE556) gets heated excessively within 5 to 6 seconds. As a result, I had to stop at the very first stage of testing.
Note that the manual ‘on’/‘off’ switch (S1) is functioning properly.
Q2. When 12V power supply to the
Q4. I have used 0.1pF and 0.01pF ceramic disk capacitors in place of 0.1µF and 0.01µF capacitors. The vendor says these will do the job. Please give your suggestion.
Q5. If I switch on mains when the water tank is empty, what time will it take to scan and start the motor relay?
Somnath Roy Through e-mail Reply to Somnath Roy by the author Parmar Latesh B.:
I am very thankful to Mr Roy for his keen interest in my circuit. The clarifications to his doubts are as follows:
a1. IC6 is getting heated due to some wrong connection around it or shorting of its two adjacent pins. Check properly. If everything is okay; the power supply may be faulty. Replace the transformer with one having a rating of 12-0-12V, 750 mA.
a2. The ‘tick-tick’ sound is not a DTMF tone generated by IC10. It may be due to the water level sensed by the probes (sen-sors) in the tank. So whenever the power to the transmitter section is switched on, the tick-tick sound is heard after 3 to 4 seconds as the level is scanned one by one.
a3. VR1 is used to adjust the time dura-tion up to which the output of IC18 should remain high. This output activates NAND gate N17 of the buzzer section.
a4. The values of 0.1pF and 0.01pF cannot be replaced with microfarads (µF). These values are much less than microfarads. The values of ceramic or polyester capacitors are always marked in picofarads (pF). For example, the values of ceramic capacitors marked as 104 and 103 are read as 100,000 pF and 10,000 pF, respectively. But these values can be converted into microfarad units. Thus, when converted into micro-farad units, 104 and 103 become 0.1 µF and 0.01 µF, respectively. (For conversion into different units, please refer to page 24 of Q&A section in April 2004 issue.)
a5. The level-scanning section will take approx. 23 seconds to scan all the levels.
This time delay is provided by IC11 and R33 and C29. There is no predetermined time to switch on the motor. One can do it at any time manually, or soon after switching on the circuit. The water level is scanned only after the power to the circuit is switched on.
provided (and indicated) for connecting the probes using wire jumpers.
Similarly, PCB for Fig. 2 is shown in Fig. 6 with its component layout in Fig. 7. Identical points (Q, R, S, T and U) Fig. 6: Actual-size, single-side PCB for Fig. 2 (PCB-2)
terminated on connector/pads need to be connected together using wire jumpers. 6V power supply including ground and DTMF output from connector Con-3 in PCB-1 is to be connected to Con-3 on PCB-2. o
circuit is switched on, after 5 to 10 seconds, a ‘tick-tick’ sound comes from the buzzer. Is it the sound of DTMF generated by IC10 when scanning the water level?
Q3. In Fig. 2, what is the function of vari-able resistor VR1 (100k)?