K2LMG/W5EUT 1-Wire Barometer -- 5/10 Volt Design
Version 2.0

The Parts List and Calibration Proceedure for Version 2.0 Barometer

Parts List

This parts list is for Version 2.0 of the K2LMG/W5EUT Barometer design shown in this general schematic. The complete schematic is in the baro20package.zip
This is for 31.0 to 28.0 inHg range, sea level to 5000ft. If other ranges and altitudes are desired use the baro20simulator.xls to find the values needed. Suggested values changes for high altitude and more resolution are listed below.

PC board
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The first 2 parts are available from Newark (www.newark.com)
U2MPX4115A or MPXA4115A
U3 DS2438Z
The remaining parts are available from Mouser (www.mouser.com) as well as others.
U1 LM358N #512-LM358N
U5 LM78L05 #511-L78L05ACZ
U4 L78M10 #511-L78M10CV
D1-D3 1N5817 #583-1N5817
D4 5 volt LED #512-MR5460
Resistors (all fixed resistors 1/4 watt metal film).
R1 100K
R3 5K pot #72-T93YA-5K
    For a 1 inHg range use10K pot #72-T93YA-10K
R4 2K pot #72-T93YA-2K
R5 10K pot #72-T93YA-10K
R6 15K
R7 2.7K
R8 5.6K (6.98K if over 5000 ft elevation)
R9 2.4K (1K if over 5000 ft elevation)
R10 2.7K
R11 2.2K
C1 1 MFD tantalum #80-T350A105K025
C2 2.2 (or 4.7) MFD electrolytic #140-XRL35V4
C3-C4 4.7 MFD tantalum #80-T350B475K016
2 gang modular connector #154-6612
Dip socket #575-199308
Sip sockets (for pots)See note #575-193110
Power connector #163-5004
Header #571-41032390

Note: The Sip socket(s) are for the pots. Needed only if they might be changed.

Parts URL: Mouser Electronics,   Digi-Key,   Newark Electronics,   Radio Shack   among many others.

Testing and Initial Calibration

It is assumed that you already have 1-Wire hardware and software working on a computer. If not you must obtain information on both at: iButton-TMEX and Developers Tool Kit
  1. Download the simulators.zip package.
  2. Run Jim's Baro20Cal.exe. You will need the VB 6.0 runtime files on your computer. If you do not have these files a search of "visual basic V6.0 runtime" on Google.com will find many free sources for them.
  3. Enter your altitude and desired low and high barometric pressures. To convert kPa to inHg divide kPa value by 3.3863 (or millibars by 33.863).
  4. Set R3 and R4 to the values with a multimeter.
  5. Connect the jumper pin to supply voltage directly to opamp U1B from the calibration pot R5. The Test position.
  6. Connect the barometer to your 1-Wire interface on your PC and run the iButton viewer.
  7. Apply power to your barometer.
  8. Set R5 to LoVin. The iButton viewer should show a voltage near LoVolt. Adjust R4 to make it be equal to LoVolt.
  9. Set R5 to HiVin. The iButton viewer should show a voltage near HiVolt. Adjust R3 to make it be equal to HiVolt.
  10. Repeat steps 8 and 9 until no more adjustment is needed.
  11. Remove power from your barometer and set the jumper to the Run position.
  12. Connect your barometer to your 1-Wire network and run your weather station software.
  13. Finish the calibration by setting the barometric pressure reading to that of a nearby airport barometric pressure.

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