OK, there are lots of threads on the LM335 but what I need is a circuit diagram on how to connect the LM335 to the K8055 so I can log temperatures (ambient room temperatures) Actually I don’t even care what the temperature is as I am only interested in the relative temperature variations over time, over a narrow temperature range (approx 10 to 30 Celsius) with better than 1 degree resolution.
Yes I know about the Velleman Temp Sensor kit but they aren’t readily available in my locale (yes I could order one in but I want my temp logger done by the weekend)
There is no easy way to connect the LM335 to the K8055.
The problem is that according to the datasheet the “Operating Output Voltage” is about 3V.
The voltage variation is 10mV/°C.
You’ll get very bad resolution.
If you connect the LM335 with a pull-up resistor to the analog input of the K8055 you will get reading about 150 due to the “Operating Output Voltage”.
The reading will change to 160 when the LM355 is heated 20°C.
The resolution is 2°C.
Hmmm, OK. What do you recommend (if anything) for less than 1 degree resolution at ‘room temperature’? I did see a circuit for an LM335 using an Op-Amp to increase the resolution but this was for an ADR101 A/D converter.
Anyway, I figure the 10 to 30 c range that I am interested in represents 2.83v to 3.03v output (a range of 0.2v) but I want to ‘amplify’ this range to the full 5v available on the K8055 but I don’t know enough to design a circuit to do it using componets that are readily available in Australia (Jaycar to be exact). (I known enough to be able to solder stuff together, identify and correctly orient components and use a multimeter but not much more…)
[quote]Also, how does the gain work? ie if I choose R8/9 for x15 does that mean that my 0.2v range becomes 3.0v?[/quote]Yes. In this case the input voltage range of the K8055 will be 5V/15 = 0.33V max.
So if you feed to the K8055 input more than 0.33V the amplifier output will stay constantly at 5V.
Yep - I’ve ordered one. I have found a suitable circuit to convert a small range on the LM335 to a full 0v-5v range at the K8055 input but I have to order parts over the internet for that as well (nothing local).
Recieved my K8067 and constructed it (along with the K8055). What I haven’t seen are recommended values for R8 and 9 on the K8055 with the K8067 attached.
What is the voltage output range per temperature on the K8067? ie is it 0v = -20c to +5v = 70c? (The supplied calculation on p12 seem to imply the minimum is -23c rather than -20c). If I am interested in the range +10c to +40c then does this equate to ~1.75v to 3.4v. K8055 gain values will be of absolutely no use to me so what do I use in place of R8/9 - Jumpers or leave them unconnected?
Is there a way to modify the output of the K8067 such that I limit its temperature range ie 0v = 10c? This way I can apply the gain on the K8055 to achieve the resolution I want on the temperature range I am interested in. ie is it possible to adjust ‘T adj’ such that 10c will output 0v? What affect will this have on the output of the unit and does this mean a linear adjustment on the forumla. Remember I am only interested in the relative temp change not absolute temp values.
You may replace the VR1 on the K8067 board with an adjustable voltage source or a trimmer potentiometer to adjust the temperature range.
At the lowest temperature you need to measure, adjust the voltage (trimpot) until the output of the board is about 0.1V-0.2V.
I have my thermometer up and running, graphing and storing its output. Just want to confirm that for the k8055 with 4x gain, in the formula provided in the manual, the /256 becomes /1024 and the the -23 becomes the new offset value based on my 0v temp setting.
How critical is the 12v input voltage? I was ‘borrowing’ a 11.7v supply from another circuit and the Temperature values were jittering all over the place. The measured output of the K8067 was +/- 0.01v but the thermometer values were jittering +/- 2c. When I had the K8067/8055 tied to its own supply at ~12.3v all was fine (+/- 0.1c)
Also, I am aware that the input voltage has an impact on the actual temperature value output, but what is the operating range of input voltage? I have my K8067 set up for 12v.
Also, tapping the 5k Trimpot I replaced VR1 with causes some changes to the voltage output. Is there a way to ‘lock’ it down? ie should I use nail polish on the screw?
The 12V supply must be very stable to get stable readings.
If you can’t get stable 12V supply, I suggest to use a 5V voltage regulator for the added trimpot.
Buy a standard 5V regulator (7805) and connect its input to 12V, connect its GND terminal to the GND and connect the output terminal to the upper end of the added trimpot. Put also a 100nF ceramic capacitor between the regulator output and GND.
See here more details how to use the voltage regulator: http://www.google.com/search?hl=fi&biw=1198&bih=784&tbm=isch&sa=1&q=7805&oq=7805&aq=f&aqi=g2&aql=&gs_sm=e&gs_upl=74812l74812l0l1l1l0l0l0l0l238l238l2-1
Is there a way to ‘lock’ it down? ie should I use nail polish on the screw?Yes, this is good idea.
OK. It is the third terminal of the trimpot. Now connected nowhere on the board.
Remove R1. It is not needed when you feed regulated voltage directly to the added trimpot.
