automated water tank

[Noj]

Hello all,

I am a tertiary student in Fiji (South Pacific), the area i live in unfortunately is prone to water cuts. however it has challenged me to try and solve the problem by designing a system that will help when there is water cuts occurring in the area. I am currently designing a automated water system whereby water is retrieved from the tank when water supply is cut off from source and water to be automatically refilled into tank when water is below certain level through the use of a motor. I have managed to design the digital section of the circuit comprising of logic gates for the water level indicator.
the operation is as follows:

• 2 inputs
• 2 outputs
• when water level drops below the first sensor, the indicator (LED 1) is "ON"
• when water level drops below second sensor, the indicator (LED 2) is turned "ON" at the same time turning "ON" the motor
• however since motor is turned "ON", the water starts to fill up and when it passes the sensor (second) the (LED 2) turns "OFF" 'BUT MOTOR IS SUPPOSE TO KEEP RUNNING'
• when water reaches the top sensor, it turns "OFF" the (LED 1) & at the same time, to turn "OFF" motor

I have designed my circuit using circuit maker software, but my problem is that when water fills up below second sensor & eventually passes it, the motor is switched "OFF" before it fills the water to the top (FULL TANK). Can someone please assist me........

Thankyou
NOJ

[durga]

in that case you can try including one more condition in your logic

check if water level == sensor 2
'off' sensor 2 ( at this point, motor as well is switching off right?)
<include this part>
if water level is not greater than sensor 1
if motor is not 'ON'
'on' motor

here you will be checking for motor status after water level crosses sensor 2, if its OFF then you again switch it on.

Is this feasible to implement??
If not may be you can wait till other CEans respond

[Noj]

thanx for the reply, however in saying that, are you suggessting that the logic be added at the output like something that i have done was that at the outputs (LED) i have fed the outputs to be inputs to a NAND gate so to respond to the motor turning "ON" when water level is below "LOW LEVEL" sensor 2. The PROBLEM is only occuring when water fills up again thus water passing sensor 2 (LOW LEVEL SENSOR) and also turning "OFF" motor. However motor is supposed to be "ON" until it reaches sensor 1 (TOP LEVEL SENSOR) thus == FULL TANK...if i can attach my circuit maker simulation.....might be better to understand......or what do you think.....

[The_Big_K]

Noj, you must first upload photos to imageshack or flickr and then enter the complete image URL [ending in .jpeg, .png] into popup that you get after clicking button in CE's post editor.

[reachrkata]

The problem is the NAND gate. Assume S1 is upper sensor output and S2 is lower sensor output, and assume that when water level reaches below any sensor, it gives logic "high" (1). You will see that when water level goes below S2, both S1 and S2 are 1, therefore NAND gate output is 0 which turns on the motor. But problem here is as soon as water goes above sensor 2, S2 gives 0, which makes NAND gate output 1 and motor is immediately turned off.

Now for the design, assume S1 is upper sensor output, S2 is lower sensor output and M is the Motor control output. Secondly, the sensor outputs are 1, when water level goes below them and 0 when water level is above them. Finally, Motor turns on when M is 1 and turns off when M is 0. X indicates "Dont care".

The logic to implement here is as follows -
1) Turn on the motor only when both S1 and S2 are 1 - which means water is below sensor 2 (therefore it is already below sensor 1).
2) Turn off the motor only when both S1 and S2 are 0 - which means water is above sensor 1 (therefore it is already above sensor 2).

In addition, you need some kind of feedback from the existing motor state because there are 2 possibilities -
a) when the water level is reducing from a full tank, S1 will be 1 and S2 will be 0, and the motor should not run.
b) But when water level is increasing from an empty tank, the same condition S1 will be 1 and S2 will be 0, but this time motor should keep running.

With these possibilities you get the following truth table.
Inputs |Output
-------------------------
M S1 S2 | M
X 0 0 | 0 - water level is full, no motor action
0 1 0 | 0 - water level is falling from full tank, keep motor off
X 1 1 | 1 - water level is empty,turn on Motor.
1 1 0 | 1 - water level is increasing from empty tank, keep motor on


From this truth table you will get the result -
M = M.S1./S2 + S1.S2
After further optimisation -
M = S1.(S2 + M)

The presence of M in the input as well as output acts as the feedback.
To explain the need for this feedback, it ensures -
1) That when water level is decreasing from a full tank and goes below sensor 1, because the present state of motor is off, its new state will continue to remain off.
2) and that when water level is increasing from an empty tank and goes above sensor 2, because the present state of motor is on, its new state will continue to remain on.

Important caveat - In your circuit, just ensure that there is a pull-down resistor of about 10k on the M signal, so thats its initial state (default logic level) is 0.

Hope you understood all this explanation. And hope this solution works.

Happy designing.

- Karthik

[Noj]

thanx Karthik for your response, it was great because you understood what i was going through. However referring to the truth table, for the two input sensors, my implementation is exactly what you have described, the use of OR gate & AND gate. this gates is functioning well for the water level indicator however I'm havinng to trouble trying to figure out how to implement a gate at the output that will turn high (LOGIC 1) when S1 = 1, S2 = 0 and again
(LOGIC 1) when S1 = 1 and S2 = 1.
In your reply you have mentioned
M
0 - water level is full, no motor action
0 - water level is falling from full tank, keep motor off
1 - water level is empty,turn on Motor.
1 - water level is increasing from empty tank, keep motor on

This is exactly what i was trying to do at the start but because the output at the motor (M) is as such, I've been stuck ever since. However thats why i have added a NAND gate being fed from the outputs of the sensor gates, and the output is being fed into an inverter which than fed into an LED acting as a motor in my simulation.

[reachrkata]

Hi Noj,

I fell i am not exactly able to understand what you have implemented in order to comment on it. Like Big K said, better draw up your digital circuit and upload it in imageshack and send us the link. We can check out what could be wrong.

- Karthik

[Noj]

Is there any possibility of an email address that i can send my circuit simulation through..........i dont understand how to use image shak...........please forgive me for this
my email add is <removed>

[godfather]

Superb explain Karthik.
Noj visit this link it may be helpful to you for uploading image.
How to add image in a post?