Comments on: LM34DZ Fahrenheit Temperature Sensor

By: Keith Neufeld

Keith Neufeld — Fri, 12 Mar 2010 12:44:19 +0000

Phew, if you follow the link to All Electronics, you can download the datasheet from them. It shows the pinout that you’re looking for.

By: Phew

Phew — Fri, 12 Mar 2010 03:33:31 +0000

i am just a beginner in electronics and i want to know the pin configuration for the LM32DZ.. thanks!

By: JimG

JimG — Wed, 12 Aug 2009 23:06:05 +0000

There's another way to scale an a/d reading that doesn't involve floating point math, but does require 16 bit variables. Lets say your a/d reading is a value of 150, which is about .732 volts / 73 degrees using a simple function such as this will allow you to scale a adc count to any value (with some limitations - see the last paragraph). By adjusting the value of fs up or down, you can fine tune the output. fs is the value for 1024 counts.


uint16_t scale_adc(uint16_t adc, uint16_t fs)
{
	uint16_t v=adc<>=1;				// divide v by 2
		if (fs&0x8000) {		// see if fs bit 15 is set
			result+=v;		// if so, update result	
		}
		fs<<=1;				// multiply fs by 2
	}
	return result;	
}
// a test program
int	main(void)
{
	uint16_t adc,fs,temp1;
	adc=150;
	for (fs=5000; fs<=5010; fs++) {
		temp1=scale_adc(adc, fs);
		printf("fs=%d, adc=%d, scale_adc=%d\n", fs, adc, temp1);
	}
	return 0;
}

running this gives:

fs=5000, adc=150, scale_adc=731
fs=5001, adc=150, scale_adc=731
fs=5002, adc=150, scale_adc=731
fs=5003, adc=150, scale_adc=731
fs=5004, adc=150, scale_adc=731
fs=5005, adc=150, scale_adc=731
fs=5006, adc=150, scale_adc=731
fs=5007, adc=150, scale_adc=731
fs=5008, adc=150, scale_adc=732
fs=5009, adc=150, scale_adc=732
fs=5010, adc=150, scale_adc=732

So a value of around 5010 would be optimum for 73.2 degrees. Going a little further, fixing fs at 5010 and varying the adc count:

fs=5010, adc=145, scale_adc=708
fs=5010, adc=146, scale_adc=713
fs=5010, adc=147, scale_adc=717
fs=5010, adc=148, scale_adc=723
fs=5010, adc=149, scale_adc=727
fs=5010, adc=150, scale_adc=732
fs=5010, adc=151, scale_adc=736
fs=5010, adc=152, scale_adc=743
fs=5010, adc=153, scale_adc=747
fs=5010, adc=154, scale_adc=752
fs=5010, adc=155, scale_adc=756

This method isn't perfect, but it doesn't require floating point math. Try to stay away from fs values that are a power of 2 (128,256,512,1024,etc).

By: bateeze henry

bateeze henry — Fri, 17 Apr 2009 13:42:31 +0000

am in uganda trying to design a LED thermometer requiring an LM34DZ temperature sensor IC but i have failed to get it. i would like alternative ICs of LM34DZ.

i will greatful for your response

By: bateeze henry

bateeze henry — Fri, 17 Apr 2009 13:27:27 +0000

iam in uganda trying to design a LED thermometer requiring an LM34DZ temperature sensor IC but i have failed to get it. i would like alternative ICs of LM32DZ

By: Keith Neufeld

Keith Neufeld — Tue, 17 Feb 2009 16:18:32 +0000

Dave, the I2C chips sound interesting, especially in SMT. Thanks for pointing that out!

By: Dave

Dave — Mon, 16 Feb 2009 23:15:22 +0000

There are quite a few temperature sensor ICs in the LM family. In addition to the analog ones, there are some which are digital (e.g., National LM75/Maxim DS75). These have an I2C bus, which means that you can
put several of them on the same I2C bus (e.g., Sprinkle them around a card, enclosure, etc.).

Dave

By: Keith Neufeld

Keith Neufeld — Wed, 04 Feb 2009 14:39:17 +0000

Jim, I don’t know why I thought there was no floating point on the Arduino — you’re clearly correct. Thanks for pointing that out.

I like the LM34DZ in part because it doesn’t require external components for preamplification or level-shifting. But I really dig your idea of feeding a different voltage to AREF — thanks!

By: Jin

Jin — Wed, 04 Feb 2009 02:57:17 +0000

I think Arduino does have floating point. I’ve used it, at any rate: http://www.arduino.cc/en/Reference/Float

A very simple improvement would be to feed the 3.3V output to the AREF pin for ~3.1 steps per degree. Slightly more involved would be to use an op amp to give you full scale for the temperature range of interest.