Anyone used the Bosch BMP085 I2C baro sensor yet ?

[ScaleRobotics]

Thanks Brian, I had not seen that sensor before. Nice catch.

Martin,

Don't know if you saw it already, but sparkfun has some C sample code here:
http://www.sparkfun.com/commerce/pro...oducts_id=9694

Sometimes it helps me to look at, even though I don't know C very well.

I ordered their board, but they are out of stock right now.

Walter

[Acetronics2]

Hi,

Also have a look to this one ...

reminds you some other ???

Alain

[mr.sneezy]

Thanks Brian, I had not seen that sensor before. Nice catch.

Martin,

Don't know if you saw it already, but sparkfun has some C sample code here:
http://www.sparkfun.com/commerce/pro...oducts_id=9694

Sometimes it helps me to look at, even though I don't know C very well.

I ordered their board, but they are out of stock right now.

Walter

Thanks Walter and Brian.

Brian I'm already committed to the Bosch sensor, and I have one on the way to me. Bare sensors are $8.95US at Sparkfun which is hard to beat.
I'd like to use it in this project as it has a good track record for use in altimeter devices. The soldering of this device shouldn't be too hard if you have some SMD experience (lots in my case). Or tip it upside down like another guy has and solder wires on top.

Walter I didn't C the C code at Sparkfun but I did find some in another website here
http://www.pixelproc.net/varios.html
I downloaded the C code, but it's all double dutch to me unfortunately. Maybe it will help you.
Walter maybe we can share some code when we have the devices.

Martin

[rsocor01]

Bare sensors are $8.95US at Sparkfun which is hard to beat.

Check this sensors out.

http://futurlec.com/Pressure_Sensors.shtml

Robert

[BrianT]

The FuturLec prices are excellent but I fear the HP03D will give highly variable results depending on incident light intensity. All silicon strain gauges are light sensitive. The HP01 and HP02 ones, coated in black, will be OK. The Intersema MS554x are light dependent even though they have opaque white 'silicone snot' covering the strain gauge element to reduce, but not eliminate, this effect.

Another trap with all these sensors is that distorting the ceramic substrate will bring out very large pressure and temperature offsets. In my experience, proper SMD reflow oven soldering does not stress the subsrtate anywhere like as much as hand soldering where the thermal stresses build up as each pin is soldered individually. I have found mounting the chip upside down and hand soldering fine 0.010 inch or 0.25 mm wire wrap wires keeps a batch tracking very well. You will not see the stress effects if you only make one or two units but if you build a batch of 100+ the difference unit to unit can be very frustrating.

The Hope HP03 has a cute feature of an on-board oscillator. I use the CCP registers of a PIC to provide the 32768 Hz MClk to the Intersema snsor but sometimes I would rather use a watch crystal direct on the pressure sensor instead of tying up a CCPWM port.

Lastly, most of the pressure sensor application notes specify a large tantalum cap across the supply. 47 uF in the case of the Intersema. The leakage current of this cap exceeds the sleep current of the sensor so don't forget that when you calculate your battery life.

HTH

BrianT

[mr.sneezy]

Thanks Brian.

Yes this is a one off project not a big batch, although hopefully many other RC model enthusiasts will build themselves one as it's part of an open source telemetry project using 2.4Ghz.

The sensor is actually available mounted on a small PCB for about $10 more. That may be the safest option.

I think the datasheet says only light through the small air hole is a problem on this sensor, so that should be easy to cover with something like carbon foam (antistatic chip foam).

Looks like I'm pioneering this sensor with PBP, hopefully you guys can help me cross the hard stuff when I get there in a week or so.
Martin

[ScaleRobotics]

Sparkfun has more of their BMP085 boards in stock now, if anyone is interested. Makes it nice to breadboard with. With the board, the cost is about the same as the Intersema. Still waiting on mine.

[mr.sneezy]

I've got my BMP085 now, and I'm using a serial LCD and a PIC12F683 to try converse with the sensor initially. I have a problem with i2c comms, and reading the datasheet it mentions 'Restart condition' between starting a conversion (temperature in this case for simplicity to see it changing) and reading the result.
Now I've not come across the 'restart condition' before with i2c chips (just EEPROMS thus far).

Is it done in the PBP i2c statements or does it need to be bit-banged ? Or am I up the whole wrong tree here altogether ?

Cheers all,
MArtin