T&L Publications

i am looking for a digital temp sensor,, i have a analog lm34 but i am looking for a digital version..
i saw some temp and humidity modules for arduino, but none are for Fahrenheit.

Checked at Digikey. For analog there are Fahrenheit choises (fewer than Celsius, but there). For digital there is no choise, just Celsius.

Makes sense. In analog converting could mean two op-amps, some resistors and compensation capacitors. In digital it is bit of programming to convert to Fahrenheit. Multiply by 9, divide by 5, and add 32. Three steps and all integers (important because most microprocessors (like Arduino, PIC, etc) don't do floating point arithmatic.

I don't quite understand what you mean by a digital temperature sensor that reports in Fahrenheit. Most analog sensors report in voltage or resistance changes and the conversion to Fahrenheit or Celsius is done with circuitry.

How do you envision a digital sensor reporting it's data? Are you expecting say a serial ascii string?

P.S. The DS18B20 is a very nice and inexpensive digital temperature sensor...The problem is that it has a 1-wire protocol interface so a microprocessor is probably required. Although it reports temperature in Celsius generally that's not a big problem since a microprocessor is generally employed so the arithmetic conversion to Fahrenheit is simple.

well here is the thing.. i built a digital temp a few years ago using the ICL7107
and a LM34 sensor...the ICL7107 was set up as a volt meter..
it worked, but it never was linear.. and i did use the recommended parts.
so i am tired of it..and want to use a Arduino nano and a temp sensor, i guess i could use analog input.. but i was thinking digital input would be better.. just can't find a suitable sensor yet...
i did see a few that had C and humidity.

dacflyer wrote:well here is the thing.. i built a digital temp a few years ago using the ICL7107
and a LM34 sensor...the ICL7107 was set up as a volt meter..
it worked, but it never was linear.. and i did use the recommended parts.
so i am tired of it..and want to use a Arduino nano and a temp sensor, i guess i could use analog input.. but i was thinking digital input would be better.. just can't find a suitable sensor yet...
i did see a few that had C and humidity.

Okay. now I got it. Problem solved. If you are using an Arduino then get yourself the DS18B20 temperature sensor of my last note and connect it to the Arduino. There is a ton of information online on how to do this. The DS18B20 is also available in waterproof probe form with a couple of feet of lead wire. It have done it with an Arduino and it works great. And you can easily connect multiple sensors on the same I/O pin since the 1-wire protocol supports it. You can get the DS18B20 on Amazon very cheap in additional to more conventional sources.

Yes, it basically reports the temperature in Celsius but the conversion to Fahrenheit is trivial in an Ardurino. Again, Google it there is a ton of information available online.

ok, great... BTW, what is the accuracy going to be ? like i said my last one was not linear at all..
not sure if sensor length was a issue or not, ( 5ft ) i had the caps that was recommended for long distance. helped some, but never accurate. and yes i did calibrate before..
anyway.
i'm going to be using the sensor you recommend, the nano, and my display ( 2" ) is going to be driven by TPIC6B595'S
since the displays are of a higher voltage than the 5v source,

thanks again.
i'll show fotos afterwards..

dacflyer wrote:ok, great... BTW, what is the accuracy going to be ? like i said my last one was not linear at all..
not sure if sensor length was a issue or not, ( 5ft ) i had the caps that was recommended for long distance. helped some, but never accurate. and yes i did calibrate before..
anyway.
i'm going to be using the sensor you recommend, the nano, and my display ( 2" ) is going to be driven by TPIC6B595'S
since the displays are of a higher voltage than the 5v source,

thanks again.
i'll show fotos afterwards..

I think the spec for the DSB1820 is 0.5 C over a pretty wide range...This may depend on the mfr..check the spec sheet wherever you buy it. No calibration should be necessary, but I guess you could fine tune small errors in the nano. I can't vouch for the accuracy, but as I recall I was happy with some rudimentary tests with ice water and boiling water. I also did some simultaneous readings of several sensors and they tracked each other almost perfectly.

I would expect if the manufacturer went to the extent of putting in an A/D converter and logic to convert those counts into Celsius values that they would have linearized it as much as was possible for the design. They may not be using a bi metal junction at all but instead tracking the forward voltage of a reference diode which is also proportional to temperature. This method is done with some big CPU chips, they actually have dedicated pins that lead to temperature sensing diode junctions and are connected to the thermal control systems chip. I'd need to do more research to claim that Vf is more linear then a Bi-Metal voltage drop but I suspect this is so.

been so busy lately at work etc..
but anyway i ordered me the DHT22
and i ordered me a pressure transducer, i want to monitor my well water pressure.
i have some giant displays, and will adapt the sensor,, it's output is voltage at pressure.. it is not digital
i could not find anything cheap in digital.. this one i ordered is good for 100 PSI , paid $20.00 for it.

i'm playing with 4x tpic6b595 IC's to drive 4 digits.. i am looking for test code for the digits, i'll be using the Arduino NANO
i need a simple code to talk to the 4 digits, something simple that can count up.. so i can make sure the digits are connected properly..
what is suggested best for the serial input ? the far right digit or the far left digit ?
thanks for any help.
after this. i'll be working on getting the DHT22 installed...

dacflyer wrote:well here is the thing.. i built a digital temp a few years ago using the ICL7107
and a LM34 sensor...the ICL7107 was set up as a volt meter..
it worked, but it never was linear.. and i did use the recommended parts.
so i am tired of it..and want to use a Arduino nano and a temp sensor, i guess i could use analog input.. but i was thinking digital input would be better.. just can't find a suitable sensor yet...
i did see a few that had C and humidity.

That brings back memories of my first digital readout thermometer before the days of present $10 units. I wanted to be able to know the temperature outside from inside the house. It turns out that simple silicon​ diode junctions are quite linear concerning changes in junction voltage drop and temperature​. I think I used a 1N4002 diode.

What I did was get the reported temperature many times and compared that to the voltage reading on the digital multimeter set to read voltage drop of diode junctions (diode setting on ohms mode on front rotary dial).

I also got a reference by using an ice bath. That gave me a confident reading for 32°F. That was a certain figure that was the beginning point of the look-up table that I gradually composed. I wrote down two figures in two columns. One was either a personally measured temperature (more on that in next paragraph), or reported temperature, and the other was the diode voltage drop reading, side by side, going down according to rising temperature.

I also obtained some more reference figures of indoor temperatures with the help of mechanical and mercury thermometers. I found that using extrapolation, I could fill in figures between 32°F and my indoor readings. I extrapolated down for cold winter temperatures, and hot summer ones, and it turned out to be linear based on my experience.

So I wrote down all the temperatures consecutively, and filled in figures based on my measured temperatures and reported ones.

A temperature figure outside of the range of my measured temperatures could have several voltage readings not because of a problem with the set-up accuracy, but because of some uncertainty concerning reported temperatures.

ok,, i got my sensor in last week "DHT22"

i got my display configured properly and i am running test code on it to count from 0000 to 9999, so all digits are working properly
with my Arduino nano..
the last few days i been trying to find code that will work with my display set up.. but no luck.. most code works with the LCD displays or the 4 digit Adafruit displays.

do with my lack of code knowledge, i been just guessing and trying to stitch things together.
i only need to see the temp displayed in Fahrenheit, i do not care for the humidity display.

and i most likely do not need any serial monitoring..
any help ? i can share my modified display code, so you know how i have things set up.

well i got my project mostly working..
had a friend help me with code.. but there is a problem with a leading zero. and there is no decimal.
temp displays ( 0757 )
also it will not display any Negative symbol for below zero temps.
so i am probably gonna need to get more code added in...

bump