which digital thermometer to use?

OakGraphics

I have been looking at the DS series digital thermometers, and I am trying to find an easy - multi thermo solution with the least amount of pins.
I see the DS1820 is a 1-wire, and it looks the simplest to set up. I essentially need 6 or so temps monitored for motor and power supply thermal shutdown circuits.
I am using a propeller for this, and plan on showing the temps on an lcd / tv screen or maybe 7-segment led readouts.

Any suggestions?

Each thermo will be about 3 to 6 feet away from the 'base', and first thought was in a star topography, but have read in the ds1820 that it might not be the best way. I could string them in parallel, and in bridge mode (drop downs of 3 feet from parallel run). I need to monitor temperatures in upwards of 125c for stepper motors.



Thanks in advance,
Daniel

ElectricAye

I've used DS18B20's for 6 foot lengths, with each sensor having its own 6 ft. unshielded cable reaching back to a "plug box" made of molex connectors, with the plug box being about 2 feet from the Propeller, and I haven't detected any problems so far.

I haven't checked lately to see if it was updated but the 1-wire object, SpinOneWire, needed a slight mod to do negative temps.

My .02 cents worth.

OakGraphics

ElectricAye said...
I've used DS18B20's for 6 foot lengths, with each sensor having its own 6 ft. unshielded cable reaching back to a "plug box" made of molex connectors, with the plug box being about 2 feet from the Propeller, and I haven't detected any problems so far.

I haven't checked lately to see if it was updated but the 1-wire object, SpinOneWire, needed a slight mod to do negative temps.

My .02 cents worth.

Thats sounds good. I would pretty much have the same rig so I will go that route. I don't expect to be in negative temps while operating it, but would still like to know the mod if you had it lying around, or I will search the forums to see what the fix was.

Sounds fun!

ElectricAye

I said...
....
I haven't checked lately to see if it was updated but the 1-wire object, SpinOneWire, needed a slight mod to do negative temps. ....

Here's the mod.· It's just the insertion of one line that reads:

temperature := ~~temperature  {Modified 9 Dec 2008 to provide negative temps.} 

PRI ReadTemperature(ThermalAddress) | temperature, degC, degF, WatchDogDS18b20
  {Read the temperature from a DS18B20 sensor.}
  {Waits up to 10 seconds for the sensor to provide data.}
  ow.reset
  ow.writeByte(ow#MATCH_ROM)
  ow.writeAddress(ThermalAddress)
  ow.writeByte(ow#CONVERT_T)
  {Reset WatchDogDS18b20 to zero...}
  WatchDogDS18b20 := 0
  repeat {Repeat until the called sensor tells us it is ready to give data...}
    waitcnt(clkfreq/100 + cnt)
    {Increment the watch dog on every pass and if the wait for a sensor exceeds
      about 1000 iterations, then there is a problem, therefore return to main program.}
    WatchDogDS18b20 := (WatchDogDS18b20 + 1)
      IF WatchDogDS18b20 > 1000 {About 10 seconds.}
        {Consider lighting up a warning LED.}
         return
    IF ow.readBits(1) 'The sensor is ready to provide data.
      ow.reset 'Say okay and prep the data line.
      ow.writeByte(ow#MATCH_ROM) 'Tell the sensor you want to match a ROM
      ow.writeAddress(ThermalAddress) 'Send out the ROM to match.
      ow.writeByte(ow#READ_SCRATCHPAD) 'Open up the sensor's scratchpad.
      temperature := ow.readBits(16) 'Read the data.
      temperature := ~~temperature  {Modified 9 Dec 2008 to provide negative temps.}  
      ' Convert from fixed point to floating point
      degC := f.FDiv(f.FFloat(temperature), 16.0)
      ' Convert Celsius to Fahrenheit
      degF := f.FAdd(f.FMul(degC, 1.8), 32.0)
      result := degF  {The result is the temperature in degrees F.}
      return 'Return to the main program...
{*** End of method ReadTemperature ***}

OakGraphics

ElectricAye said...

Here's the mod. It's just the insertion of one line that reads:

cool beans - literally! Okay I will try it out when I get the thermos. I am ordering them from ebay. 10 of them for 16$.