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Temperature measurement using 89c51

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garg29

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Dear friends,
I am making a simple temperature measurement device. I’m using LM35 with 24-bit ADC and 89c51. Please tell me how to feed value from 24 bit adc to 8 bit registers of 89c51 and how to perform calculations for decimal (I’m designing for 0.1 degree Celsius accuracy). I have to display the result on 7-segment displays.
Thanks.
 

i think the best solution is using cascaded connected paralel in serial out shift registers. i dont remember part number but you can easily find. implement an algoritm that makes recieve serial data and bcd conversion, then put value 7seg or lcd or something. if you are usin C , it is easier.
 

The LM35A will give you a worst-case accuracy of ±1°C over its temperature range -
clearly not adequate for your design specification.

A 24-bit ADC has a resolution that is way too much for your needs.

I think you should revise your design parameters...

/Rambo
 

for %0.1 presicion look senserions sensors.
**broken link removed**
 

K
garg29 said:
Dear friends,
I am making a simple temperature measurement device. I’m using LM35 with 24-bit ADC and 89c51. Please tell me how to feed value from 24 bit adc to 8 bit registers of 89c51 and how to perform calculations for decimal (I’m designing for 0.1 degree Celsius accuracy). I have to display the result on 7-segment displays.
Thanks.

Yeah, I'm agree with previous post, LM335 give you accuracy of ±1°K, so using 24-bit ADC is too much enough for your application (it leads to a very wide range of temperature 0 ÷ 2^24°K. Do you really need to measure a temperature within this range??? Even if you measure from -273°K - impossible with LM335).

I think 8 bit ADC is a wise choice (ADC0804)!

Just a recommendation!
 

try reading maszidi . A clear explaination is given regarding interfacing with temp. sensors but he has used Lm35, but the basics are pretty much the same.,
 

i thinnk the 24 bit adc is too much for your application..
besides if u decided to use lcd u might face some problems because of the ios number will be limited
 

All of posts above have been giving you advices on how not to employ 24-bit AD to performe this job.
An I agree. You have chosen wrong device (LM35) and to many bits (24, it looks like half of that would be enough).
But elaborting on how to streem 24-bit word into 8-bit device is totaly different issue.
Here is how you do it:
Save them as memory locations of: MSB (most significant byte), MSB (meiddle s b ) and LSB (Low s b). From now on you have a 24-bit word saved as 3-byte representaion...
 

Using 24 bits for an ADC with a 10mV/degree C is quite overkill.

But if you insist using one, here is the technique. Allocate a memory location (8 bits) for every 8 bits of ADC, make a loop and and start it with 8, decrement it and if the value equals 1, it means byte 1 is already full, then shift your memory pointer to byte 2, then do the loop again, do the same for byte 3.
 

Hi

Using a 24 bit ADC to measure 0.1°C with LM35 is like measuring with a micrometer, and cutting with an ax. If you need a cheap solution, using 89c5x, you should consider a dual slope converter, that you can implement using a simple integrator and a comparator tied to an INTx pin. You can find lots of info on this around the net.

Best regards
 

You can use Microchip's TC74 Serial Digital Thermal Sensor directly. No need for AD converter, as TC74 is a complete sensor with I2C interface. A cheap and fast solution if the characteristics are enough for your application.
h**p://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en010749
 

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