K2LMG/W5EUT 1-Wire Barometer -- 5/10 Volt Design
The Parts List and Calibration Proceedure for Version 2.0 Barometer
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
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.
Ask for latest Jennings Barometer|
$4 plus shipping of approximately $1.50.
|The first 2 parts are available from Newark (www.newark.com)|
|U2||MPX4115A or MPXA4115A|
|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).
|R3|| 5K pot ||#72-T93YA-5K|
| For a 1 inHg range use||10K pot|| #72-T93YA-10K|
|R4|| 2K pot|| #72-T93YA-2K|
|R5|| 10K pot|| #72-T93YA-10K|
|R8|| 5.6K ||(6.98K if over 5000 ft elevation)|
|R9|| 2.4K ||(1K if over 5000 ft elevation)|
|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|
Note: The Sip socket(s) are for the pots. Needed only if they might be changed.
Parts URL: Mouser 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
- Download the simulators.zip package.
- 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.
- 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).
- Set R3 and R4 to the values with a multimeter.
- Connect the jumper pin to supply voltage directly to opamp U1B from the calibration
pot R5. The Test position.
- Connect the barometer to your 1-Wire interface on your PC and run the iButton viewer.
- Apply power to your barometer.
- Set R5 to LoVin. The iButton viewer should show a voltage near LoVolt. Adjust R4 to
make it be equal to LoVolt.
- Set R5 to HiVin. The iButton viewer should show a voltage near HiVolt. Adjust R3 to
make it be equal to HiVolt.
- Repeat steps 8 and 9 until no more adjustment is needed.
- Remove power from your barometer and set the jumper to the Run position.
- Connect your barometer to your 1-Wire network and run your weather station software.
- Finish the calibration by setting the barometric pressure reading to that of a nearby
airport barometric pressure.