1-wire barometer DIY

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1-wire barometer DIY

Postby Snelvuur » Fri Jul 25, 2008 1:11 pm

http://davidbray.org/onewire/barometer.html

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This article describes details for constructing a 1-Wire Barometer which will work on a Dallas Semiconductor Corporation 1-Wire network.

The reason for this second version is that the transistor level-changer of the original design was found to be temperature sensitive. If you have constructed the original version (V1.0) you can modify it according to the diagram shown below. This involves removing the transistor and 5 resistors, then rewiring it with 6 new resistors.

The goal of this design was to make a simple reliable 1-Wire barometer with reasonable pressure resolution and one which could be constructed without a specialized printed circuit board by a hobbyist.

This design uses a Motorola MPX4115 Silicon Pressure Sensor, a Dallas Semiconductor DS2438 Smart Battery Monitor (to perform 1-Wire analog to digital conversion), an operational amplifier, a voltage regulator, a diode, and several resistors and capacitors.

Construction of this circuit should not be attempted unless construction of IC circuits on project boards similar to this have been done before. It is a pains taking task.

This must be considered a work-in-progress. To date only three of these barometers have been constructed. Two of them are located at altitudes under 500 feet, and one is located at 9500 ft. All are newly constructed and not fully calibrated.

As more barometers are constructed feedback is requested, and improvements in the design are welcome.
Limitations:

* The circuit requires an additional power source other than that of the 1-Wire network. The MPX4115 requires about 7 ma of current. This is more than a 1-Wire network can provide without an elaborate circuit to store parasitic power from the 1-Wire network for short burst of current for pressure measurements.

* The resolution of the barometric pressure is somewhat greater than ideal. With a pressure range of 28.0 to 31.0 inHg the resolution is about 0.015 inHg. If a reduced pressure range of, say, 28.7 to 30.7 is tolerable a resolution of 0.01 can be achieved.
More resolution is not possible because the 5 volt MPX4115 has a range of 0 to 115 Kpa (~0 to 34 inHg), the D2438 is a 10 bit A/D but has a voltage range of ~1.5 to 10 volts, and normal operational amplifiers have a linear range of 0.75 to 3.5 volts (in 5 volt applications). Together all three devices are somewhat incompatible for constructing a single 5 volt power supply barometer. By keeping the voltage to 5 volts allows the use of a Simon Hub.

// Erik (binkey.nl)
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1-wire barometer DIY

Postby Dowser » Fri Jul 25, 2008 1:45 pm

Shamelessly ripped from Hackaday.com! :)

But you also copied their mistake.
You both took the link and information for the 1.1 version of the hack instead of the 3.0 version...
http://davidbray.org/onewire/baro2030.html

Personally I would buck out the extra money for a pre-made, pre-calibrated TAI8570 from http://www.aagelectronica.com/aag/index ... =p_21.html or any other place where you can find 1-wire modules.

//Markus
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1-wire barometer DIY

Postby Snelvuur » Fri Jul 25, 2008 1:48 pm

hackaday indeed.. sometimes i copy the source with it, sometimes i dont.. *lazy*

// Erik (binkey.nl)
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1-wire barometer DIY

Postby TANE » Fri Jul 25, 2008 2:33 pm

why go for a $70 1-Wire Barometer if you can have Oregon BTHR918N for $40?
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1-wire barometer DIY

Postby Snelvuur » Fri Jul 25, 2008 3:10 pm

i know, but diy projects are always fun to see.. even though it might cost more.. (i would just buy oregon though, in fact i allready did)

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