PIC16f690, initialisation of ports, LEDS,reading from a pin

[jpanhalt]

The required range is 2 to 50 cm. None of those detectors cover that range. The Vishay device listed first says up to 4 or 5 cm, but the datasheet doesn't seem to support that.

I don't see how reflection at an angle is going to work with a liquid that potentially has ripples. All of the packaged devices seem to be for solids, like sheets of paper.

John

 

[be80be]

What you used is not Ir it's a laser ?


**broken link removed**

 

[jpanhalt]

What you used is not Ir it's a laser ?

It's all just light. The principle is the same. There are a great number of liquids that are reasonably transparent in the near infrared, at least to 940 nm . The liquid in this case is unspecified.

My point was that there is a reasonable chance the light will not be reflected from its surface more than from an underlying surface of greater reflectivity, particularly when the liquid level is low. That is basically what my experiment showed. Obviously, there is always reflection at an interface, such as an air-water interface, but if that reflection is about 10% or less, and reflection from a surface a few cm deeper is 60%, the detector is going to read the latter, not the former. I am sure the surface reflected some of the light in my experiment, but its intensity was swamped by the reflection from the basin.

John

 

[be80be]

It's not the same a laser is no where the same as IR light. A laser have the same frequencies and identical phase and have narrow wavelength spectrum. The IR light has wide wavelength.So not the same power of a laser. You can get Ir laser but it's not going to work it would shoot thew the water before it bounces back.

But a Ir led will bounce off the water we done been down that road before. I'll dig up what i found the last time.

 

[jpanhalt]

But a Ir led will bounce off the water we done been down that road before. I'll dig up what i found the last time.

Please do. All of my comments were related to the OP's concept of determining distance using TOF with reflected light from an unspecified liquid's surface. At least that was clearly the focus of my comments.

I am anxious to see how you did that without a laser and using IR. I hope you can find those experiments.

I am not denying that light, including IR, reflects off or can be scattered by water. Anyone who is not blind knows that -- actually, blind people experience it too. What I am suggesting is that the OP's projected design, as vague as it is, should have some basic validation done of its underlying assumptions before wasting a lot of effort on building it.

As for what you imply about laser light grossly deviating from Beer's (Beer-Lambert) law, can you provide any references to that? (Again, I am talking about the sort of intensities that are used for these instruments.)

John

 

[fantabulous68]

rjenkins from AAC suggested some methods and i think this would be a suitable approach for me. This is what he suggested:

For 50cm you would probably be best off using the strength of the reflected IR signal.

Switch the emitter on&off at a steady rate (tens of hz?) and measure the IR sensor output with one of the ADCs in the PIC for both emitter on & emitter off.

The difference gives you the signal due to the emitter, cancelling any ambient illumination.

You can then calibrate that (using a look-up table?) to actual distance.

I want to go with this method. Ok so now that means starting from scratch with my hardware.

 

[fantabulous68]

Default
The required range is 2 to 50 cm. None of those detectors cover that range. The Vishay device listed first says up to 4 or 5 cm, but the datasheet doesn't seem to support that.

I don't see how reflection at an angle is going to work with a liquid that potentially has ripples. All of the packaged devices seem to be for solids, like sheets of paper.

im going to ask my lecturer today if he would pls allow me to use the sharpgp2d12. And decrease the range of the sensor from 50cm to about 35cm

Any 1 has a clue if its suitable for liquids???

The Sharp GP2D12 is an analog distance sensor that uses infrared to detect an object between 10 cm
and 80 cm away. The GP2D12 provides a non-linear voltage output in relation to the distance an object
is from the sensor and interfaces easily using any analog to digital converter

i got the above from the attached parallex datasheet.

Im not going to angle the sensor. The sensor will be perpendicular to the surface of the liquid

Will the sensor work on pic micro or the AVR atmel microcontroller?
Features
• High immunity to ambient light and color of object
• No external control circuitry required
• Sensor includes convenient mounting holes
• Compatible with all BASIC Stamp® and SX microcontrollers

 

[be80be]

You can use Sharp GP2D12 with any uC. You first said it was not a option
You first posted you couldn't read a switch on port then later you post it's a Ir module
If your not careful your going to get options run away here.

This is some what how the the sharpGP works

For 50cm you would probably be best off using the strength of the reflected IR signal.

Switch the emitter on&off at a steady rate (tens of hz?) and measure the IR sensor output with one of the ADCs in the PIC for both emitter on & emitter off.

The difference gives you the signal due to the emitter, cancelling any ambient illumination.

You can then calibrate that (using a look-up table?) to actual distance.

 

[fantabulous68]

Sorry, yeah im just worried now, coz i spent alota time coding for the hardware i tested.

i just need to decide on something solid to stick with since my other solution is not going to work.

 

[blueroomelectronics]

The Sharp rangefinder needs an A/D input. The BASIC stamp doesn't have one.

 

[fantabulous68]

I want to

thank all of you'll VERY MUCH

. Its better that i found out now than a week b4 my project is due that my TOF solution would fail. I explained that no microcontroller timer is fast enough to time light and got permission to use the sharpGP2D12.

any suggestions for a suitable microcontroller in the atmel or pic for doing ADC on sharpGP2D12? the range of the sensor is variable from a couple of centimeters to about 50cm.

 

[be80be]

It will work with the 16f690 it has adc Your using it I would keep using it.

 

[birdman0_o]

Be careful of the slope the sensor creates, it is not linear.

They provide the equation on the datasheet or you can use a look up table, the lookup table would be much much easier (less accurate though).

 

[Nigel Goodwin]

Be careful of the slope the sensor creates, it is not linear.

They provide the equation on the datasheet or you can use a look up table, the lookup table would be much much easier (less accurate though).

I don't see why you would think a lookup table would be any less accurate?, you generate the lookup table from the equation, so it's exactly the same.

 

[birdman0_o]

You are right, in my mind there would be less values in the lookup table, however since the ADC is limitted to 10 bit, you would just need to make up a big lookup table for it to be just as accurate.

 

[fantabulous68]

Nigel says:

The 16F is 14 bit, and the 18F is 16 bit, this allows the 18F series to have a larger instruction set - the 18F has an instruction set that's optimised for use with C, and MicroChip even provide a free C compiler for it. Essentially it's a higher end version of the 16F, and runs faster as well, with an internal PLL that can run four times faster than the external crystal.

So im wondering is it possible for me to modify this code to suit the pic16f690???because i already got my lcd display working on the 16f690. is there any major differences that would affect this code on the 16f690???eg the line with:
// load ADC value in 16bit math var

I use hi-tech universal c compiler in mplab. I know i got to configure in mplab compiler.

//*********************************************************
/*  Junebug_Serial4.c    RomanBlack.com 19th July 2009.

	Junebug 18F1320, uses my "zero error 1 second timer"
	system to generate a 2 second interval, then every
	2 seconds it reads an analog voltage from a
	Sharp GP2 distance sensor and converts it to decimal
	distance, then sends that data as a text string to PC
	via bitbanged serial out. It also flashes Junebug LED1
	everytime it takes a distance sample.

	Code for MikroC, config handled by MikroC compiler;
	_INTI02_OSC_1H
	_WDT_OFF_2H
	-MCLRE_ON_3H
	_LVP_OFF_4L
	_PWRT_ON_2L

*/
//*********************************************************

// functions declared
void calc_distance(void);
void send_serial_message(void);
void send_serial_byte(unsigned char);

#define PIN_SER_OUT LATA.F3		// which pin for serial out (PORTA.F3)
#define SER_BAUD 51				// TMR3 (1Mhz/19200 baud) = 52
								// tested; works from 49 to 53, using 51

unsigned char i;		// used for looping

unsigned char cm10;		//
unsigned char cm;		//

unsigned int math;		// used for voltage calculations
unsigned long bres;		// for bresenham 2-second timer system


//---------------------------------------------------------
void main()
{
	// setup the PIC 18F1320
	OSCCON = 0x72;      	// internal osc, 8MHz

	PORTA = 0;
	TRISA = 0b10000010; 	// RA7 high imp, RA3 is serial out,
							// RA1 is ADC input measuring VR1
	PORTB = 0;
	INTCON2 = 0;            // PORTB pullups ON
	TRISB = 0b00000000; 	// PORTB not used

	ADCON0 = 0b00000101;	// ADC ON, RA1 is ADC input
	ADCON1 = 0b01111101;	// AN1 is ADC input
	ADCON2 = 0b10100010;	// right justify, 8Tad, 32Tosc

	T1CON = 0b00010001;     // TMR1 is ON, 1:2 prescale, =1MHz

	T3CON = 0b00010001;     // TMR3 is ON, 1:2 prescale, =1MHz

	// main loop here;
	while(1)
	{
		// wait for 2 seconds, uses TMR1 free running at 1Mhz
		while(!PIR1.TMR1IF);    // wait for TMR1 overflow
        PIR1.TMR1IF = 0;		// clear overflow flag
		LATA = 0;				// all LEDs off
		
		bres += 65536;			// add 65536uS to bres value
		if(bres >= 2000000)		// if reached 2 seconds!
		{
			bres -= 2000000;	// subtract 2 seconds, keep error
		
			// flash Junebug LED1,  RA0=1 RA6=0 RA7=hiimpedance
			LATA.F0 = 1;			// LED on

		    // read the ADC voltage RA1 (Sharp GP2 sensor)
		    ADCON0.F1 = 1;		// set GO bit, start doing ADC
		    while(ADCON0.F1);	// wait until ADC done
			calc_distance();		// convert ADC value to distance
			send_serial_message();	// send message back to PC!
		}

	}
}



//---------------------------------------------------------
void calc_distance(void)
{
	// from the Sharp datasheet the analog voltage is
	// the inverse of distance, so distance can be calculated
	// d = (1 / volts) then just scaled to suit the sensor

	[B]// load ADC value in 16bit math var[/B]
	math = ADRESH;
	math = (math * 256);
	math += ADRESL;

	// now invert it; (1 / volts) use (6050 / volts) for scaling
	math = (6050 / math);
	if(math >= 2) math -=2;		// fix linear error (-2)
	if(math > 99) math = 99;	// max limit at 99cm

	// convert from 0-99 to 2 decimal digits, 0-99cm
	cm10=0;
	while(math >= 10)
	{
		cm10++;
		math -= 10;
	}
	cm = math;
}


//---------------------------------------------------------
void send_serial_message(void)
{
	// send message and number to serial port
	send_serial_byte('J');			// send ascii text
	send_serial_byte('u');
	send_serial_byte('n');
	send_serial_byte('e');
	send_serial_byte('b');
	send_serial_byte('u');
	send_serial_byte('g');
	send_serial_byte(' ');

	send_serial_byte('G');
	send_serial_byte('P');
	send_serial_byte('2');
	send_serial_byte('=');

	send_serial_byte('0'+ cm10);	// send number as ascii text 0-9
	send_serial_byte('0'+ cm);	// send number as ascii text 0-9
	send_serial_byte('c');
	send_serial_byte('m');

	send_serial_byte(13);			// send carriage return/linefeed pair
	send_serial_byte(10);			//  to start a new text line

}


//---------------------------------------------------------
void send_serial_byte(unsigned char data)
{
	// this manually sends a serial byte out any PIC pin.
	// NOTE! serial is inverted to connect direct to PC serial port.
	// baud timing is done by using TMR3L and removing
	// timer error after each baud.

	i=8;						// 8 data bits to send

	PIN_SER_OUT = 1;			// make start bit
	TMR3L = (256 - SER_BAUD);	// load TMR3 value for first baud;
	while(TMR3L.F7);			// wait for baud

	while(i)			// send 8 serial bits, LSB first
	{
		if(data.F0) PIN_SER_OUT = 0;    // invert and send data bit
		else		PIN_SER_OUT = 1;

		data = (data >> 1);			// rotate right to get next bit
		i--;
		TMR3L -= SER_BAUD;      // load corrected baud value
		while(TMR3L.F7);        // wait for baud
	}

	PIN_SER_OUT = 0;		// make stop bit
	TMR3L -= SER_BAUD;		// wait a couple of baud for safety
	while(TMR3L.F7);
	TMR3L -= SER_BAUD;
	while(TMR3L.F7);
}

 

[be80be]

That shouldn't be to hard to use with hi-tech

 

[blueroomelectronics]

I would test the sensor before proceeding. A multimeter, a sink with water and a 6v lantern battery should do the trick.

 

[fantabulous68]

yeah ill do that as soon as the component arrives Bill. Would someone pls tell me how would the the 16-bit math var in the code above be affected if i use the pic16f690 which is 14-bit?

 

[Nigel Goodwin]

yeah ill do that as soon as the component arrives Bill. Would someone pls tell me how would the the 16-bit math var in the code above be affected if i use the pic16f690 which is 14-bit?

The 16F690 is an 8 bit processor, it's the instruction width that's 14 bit.

16 bit maths just means you use two 8 bit registors instead of one 16 bit one.