Monitoring 15 thermistors by computer

Hint: Multi-channel ADC.

D from BC myrealaddress(at)comic(dot)com British Columbia Canada

Or single channel ADC plus two 74HC4051. Possibly you can also use the sound card with an excitation frequency of a few kHz and measure the amplitude with its input. Saves the ADC. Other than the 74HC4051 and some jelly bean parts that would be almost free. But someone has to write the software ...

Depending on what accuracy you need you might need to use four 74HC4051 in order to calculate out its Rdson, since sound cards have a fairly low input impedance.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

What about dallas 1 wire temp sensors, no analog interfacing required.

google around there are quite a few examples on how to use them

anks, Mike

Hi Mike, I use this program with Dallas/Maxim hardware. It will do everything you want including alarms.

Dave

anks, Mike

One thing the other two replies haven't mention is how to measure the change in resistance with temperature of your thermistor. One method is supply a constant current to the thermistor and then measure the voltage drop across the thermistor. This method requires a constant current supply for each thermistor. Depending upon your accuracy requirements you may be able to measure the voltage drop at the power supply. But if your accuracy requirements are high you will need to run 4 wires to each thermistor,measure the voltage drop at the thermistor and use an analog to digital converter with a differential input. A second method is to connect the thermistor in Wheatstone bridge configuration. With this method you need one constant voltage power supply, 3 precision resistors for each thermistor and a differnetial input analog to, digital converter.

I hope I have scared you away from using thermistors to measure temperature. A much better approach is to use Maxim one wire temperature sensors. See

The temperature range of one wire temperature sensors is -40 to 85 degrees Centigrade.

Often you can get by with a simple trick: Use a known resistors in series with each thermistor and either supply them all with a constant voltage or measure that voltage. 15 thermistors leaves one mux channel free to do that so Mike could save the 50c or so for a regulator circuit ;-)

Done it many times, works. Of course this is not going to yield super scientific precision.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Thanks guys, I'll mull over these ideas and see if I can get something put together. Mike

r.

anks, Mike

g put

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Mike

Try this...

Try this...

That's nice, but I'm looking for the $49.99 version if I can't find the $24.99 version. Mike

r.

anks, Mike

g put

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Mike

The following Web page has some good information that can help you evaluate if the one wire route is suitable for your application.

Howard

r.

anks, Mike

g put

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Mike

Another approach is to use the Arduino open-source electronics prototyping platform. See

for an overview of the Arduino platform. The item we are interested in is the Arduino Duemilanove. See This prototyping platform has a microprocessor, 14 digital I/O pins, 6 analog input pins, a 10 bit analog to digital converter, and connects to a PC with a USB cable. The cable is used to download programs to the microprocessor, send data to a PC and to supply DC power to the board. Here is a link to a page that demonstrates how the Arduino platform can be used to measure temperature with a thermistor. Or for one wire temperature sensors see: If you need more than 6 analog input channels analog multiplexer ICs like the 4051 or MC14067can be used to increase the number of analog inputs. One person used the MC14067 to increase the number of analog input channels to 96.

But the biggest selling point is the Arduino Duemilanove. only costs $35 plus shipping.

Howard

Hi Mike, I use this program with Dallas/Maxim hardware. It will do everything you want including alarms.

Dave

Hi Dave, I've dowloaded that program and the update and language pack. I can't open the .lng file exgtension. What do I use? I couldn't locate help file in the program. Can you give me some guidance? I want to see if I can set it up to do what I want, before I order hardware. Thanks, Mike