liquid level controller project

[zano]

hie im doing a project on liquid level controller,can any one help me with a code.im using a continouos liquid level sensor made by Milone technologies. im using the adc converter on PIC16F887. the level of the liquid should be displayed on an lcd.

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[johntabb]

have you tried anything yourself yet?
do you have any idea what you would like to do within the controller.
a 16f887 is quite a big chip for just a level controller and a display.

You will get a better response if you show what you have done so far, and what you are trying to achieve.
including a reasoned description of how you think the project will work.

regards John

[zano]

hie thanks yaah this pic is a big chip to use my supervisor advised me to use this chip for scalability. this controller must send a control signal to a relay to either start or stop a motor pump.

i had come up with a program to first come up with the voltage levels that would be send to the pic by the sensor, i need to then convert these voltage levels to percentages. when tank is full the voltage level should be 0.145V and when its empty it should be 1.078V.

here is the code that i came up with
Device 16F887
Xtal 4

LCD_DTPin = PORTC.0
LCD_RSPin = PORTC.4
LCD_ENPin = PORTC.5
LCD_Interface = 4
LCD_Lines = 2
LCD_Type = 0

Declare Adin_Res 8
Declare Adin_Tad 8_FOSC
Declare Adin_Stime 100

Dim ADC_RESULT As Float
Dim ADC_TOTAL As Float
Dim ADC_CHANNEL As Byte
Dim ADC_LOOPS As Word
Dim TEMP As Word
Dim LAST_RESULT As Float
TRISA = %00000001 ' Configure AN0 (PORTA.0) as an input

ADCON1 = %10000000


DelayMS 150
Cls

ADC_LOOPS = 200

LAST_RESULT = 0
Main:
Print At 1,1, "TESTING..."


ADC_CHANNEL = 0


ADC_RESULT = ADIn ADC_CHANNEL

Print At 2,1,Dec3 ADC_RESULT, " Volts"

GoTo Main

ADC_AVERAGE:
ADC_TOTAL = 0
For TEMP = 1 To ADC_LOOPS

ADC_TOTAL = ADC_RESULT + ADC_TOTAL
Inc TEMP
Next
ADC_RESULT = ADC_TOTAL / ADC_LOOPS
Return

[wastrix]

You can use this expression to get a percentage from that voltage range you specified:

percent = 100-((x-0.145)*107.18)

Where x is the voltage.

Note:
- at 8 bit resolution over the range 0.145-1.078V, you will get fairly poor resolution.
- you will need to split the expression above over two or more lines.
- you may find that you will need to round the result.
- the code you have retrieves a number from 0-255, not volts. You should modify the above expression to work with the raw data.

[johntabb]

These may be the ramblings of a Mad Man,
I haven't checked, but most big chips of this nature allow you to use a reference voltage to extens the scale of the AD port.

If you were to create a reference voltage, with say a Reverse biassed Zener, or a Forward Biassed LED. and connect this to the reference port, then configure the chip to use the reference to scale the AD port, your full scale reading on the AD port would be Reference voltage, not supply votlage so if you used a RED LED, the reference voltage would be in the region of 1.8volts,

and your level measurement voltage would have much better resolution.

to activate the motor, use an N channel FET, as a lOW SIDE SWITCH to drive the relay, it's likely that a 1megohm pull down resistor between the Gate and ground will stop the relay accidentally switching on, and if you drive the Gate from a Pic Pin, the FET should switch on when the output port goes high...
make sure that the 0volts of thge pic circuit is connected to the 0volts of the relay control circuit. and it's good policy to have a reverse biassed diode in parallel with the relay coil, to absorb any back emf when the relay switches.

regards JOhn

[wastrix]

I haven't checked, but most big chips of this nature allow you to use a reference voltage to extens the scale of the AD port.

This can be done, but be VERY careful that you read the electrical specifications in the datasheet, there is a minimum value for VREF, usually around 2.5-3V but different devices have different specs. If you go below this VREF voltage you just get garbage.