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Old Mar 29, 2010, 01:34 PM
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Originally Posted by billpa View Post
...in theory it should work at lower speeds. But we know how that goes.
True. But there's really only one way to find out. I may be ordering a sensor from you folks soon, factory-set for 3rd-party mode (just mention that in the comment field when ordering?). I'd also like to second the request for an interpretation of the raw data, as ultimately I'd use this more as a detailed pressure sensor than the altitude (very non-standard use from your POV I realize).

What are the pressure/altitude limits on it? How high can I expect it to work?

Quote:
The sensor will work at 4.3V. I am not sure that 20mA would be enough.
If it's not too much more, the NXT can probably handle it. The spec calls for a sensor to draw no more than 20 mA, but the limitation is really one applied to all four input ports together. So you could (in theory, again) run a single sensor pulling 80 mA

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Old Mar 29, 2010, 01:36 PM
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Brian, yes, just mention in the order notes that you want the 3rd party mode.

Re the raw data, that's a tough one for us, for a lot of reasons, sorry.

Re the altitude limits, the limit is 10K feet.
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Old Mar 29, 2010, 03:34 PM
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Quote:
Originally Posted by billpa View Post
Re the raw data, that's a tough one for us, for a lot of reasons, sorry.
No problem - I can see several reasons why this could be a problem, and I understand completely (having worked with LEGO, I understand perhaps more completely at times than I like ). I'm still tremendously happy that you folks were willing to open up your hardware to this level... and on top if it, help us out with interfacing it! Thank you again!
Quote:
the limit is 10K feet.
So I can max this thing out on hikes in the Rockies, but it should still give me some idea of altitude during anything lowish to medium altitude. Very cool. Thank you.

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Old Mar 30, 2010, 09:42 AM
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I have not tried slowing down the bit clock for the sensor that much (9600bps)...but on a somewhat larger scale I have done a lot of "register banged" communication with the sensor successfully.

In other words...my communication might have been

0xE8 (sent out at 100-400khz)
(several seconds pause)
0x07 (sent out at 100-400khz)
(several seconds pause)
(restart)
(0xE9) sent out at...
(pause)
read byte (at 100-400khz)
(pause)
(ACK)
(pause)
read byte...

If that works..I can't imagine the thing not liking a slower bitrate either. You might have trouble if you were doing this over DOW / one-wire serial (VERY critical timing dependencies) but I2C should tolerate slower speeds than you will. I'm not aware of a timeout being allowed in the spec.

In fact, it's possible to "crash" the bus by terminating communication at the wrong time - the slave might end up holding SDA low indefinitely. Generally the only way to clear this is to either power cycle or manually pump the SCL line (since most I2C implementations will not deal well with a stuck SDA).

In my own case, I will continue using the ET altimeter for its intended uses (datalogging and OSD) but it was not adequate for the project I built - an automatic altitude manager for helicopters. I built my own sensing unit with a current production sensor.

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Old Apr 14, 2010, 01:52 PM
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sorry, error
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Old Oct 07, 2010, 12:44 AM
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I have a question regarding the output in 3rd party mode for the altimeter. Currently, it zeroes itself when turned on, which is good. But, I can't seem to get negative values from the device (say if I take off on a cliff and fly in a valley). Am I doing something wrong or is this how it is meant to work? The guy doing the tests on his staircase seemed to have negative values, so I'm assuming that I'm wrong haha.

Also, I wish I knew I could have got you to program the sensors in to 3rd party mode before being sent No matter, I'm sure I'll find a use for the e-Logger in the future.
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Old Oct 12, 2010, 01:00 AM
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Hi, sorry about the elogger programming requirement.

Re negative values, that's not supported in the "third party" mode. Sorry about that!
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Old Oct 21, 2010, 09:54 PM
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No worries on both counts. Just thought I'd make sure I wasn't doing anything wrong.

As it's a 16bit value for the height, have you thought about making it signed? Your range would still be +- 32,000ft or km/h, which is more than enough for the specs of the system anyway. Is this a possible addition for the next firmware update in "third party" mode? I can't see why anyone would be against it.
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Old Oct 21, 2010, 10:46 PM
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Yes, we'll look into that. Good suggestion.
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Old Nov 10, 2010, 07:13 PM
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After some initial testing, I found it would be VERY handy to have negative values. Is there any chance this could be added sooner rather than later?
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Old Nov 12, 2010, 12:10 AM
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Hi, one thing I need to clarify - we can't update the sensors remotely with this new feature. It's something we'd have to add to our firmware, which would then be programmed into future sensors. We're in the process of doing this now.
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Old Jan 22, 2011, 01:34 PM
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I am sitting here with a elogger v3, and a airspeed microsensor V3

When i try to put it into third-party-mode, by "advanced" -> "custom hardware settings" -> "use my airspeed sensor with 3rd, etc..."
i then get a sequence of 0-1-2-3-4-5-6-7-8-9 in the display on the microsensor
Which i assume to be indication of 3.rd party mode selected.

However, the sensor still shows good data when i select live mode in the data recorder.

And more importantly i can't access the sensor on 0xEA

Is it still in normal mode, or ... ?
and how do i get it into 3.rd party mode, if the above is not the way to do it ?
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Old Jan 23, 2011, 05:50 PM
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It cost me my weekend, but I have a reading out of the sensor, and seeing this data actually made me ecstatic! Thanks to you all for your contribution in this thread, I would never have done it on my own!

I interfaced the altimeter sensor with an Arduino board, using the wire.h library.

Here is the code, as it might be of interest for someone, who knows:
#include <Wire.h>

#define ALT_ADDRESS (0x74)
boolean DEBUG = true;
#define I2C_WRITE_BIT (0x00)
#define I2C_READ_BIT (0x01)

void setup() {

if(DEBUG){
Serial.begin(9600);
Serial.println(ALT_ADDRESS); delay(2000);
}

Wire.begin();
}

void loop() {
altitude = read_sensor();
if(DEBUG){
Serial.println(altitude); delay(200);
}
}

int read_sensor(){
int data = 0;
Wire.beginTransmission(ALT_ADDRESS);
Wire.send(I2C_WRITE_BIT);
Wire.endTransmission();

Wire.beginTransmission(ALT_ADDRESS);
Wire.send(0x07);
Wire.endTransmission();


Wire.requestFrom(ALT_ADDRESS,2);
bitavailable = Wire.available();
data = Wire.receive();

return data;

}


I was stuck for a long while until I read in this thread that the address might be coded on 7bits sometimes, and that is case here. Once I used 0x74, instead of 0xE8, I started to have readings (with a few tears of joy I admit).

Now, these readings are far from steady... The device is set in m, and it would vary easily by +/-5 units. If I force the pressure to change on the sensor (just using silicon tube that I pinch with my finger on the pressure sensor), I can see the reading changing - that tells me that I am looking the right address.

Could that be that I am not looking at the right number of bits (2 here, but I tried with 1, it was showing something as well...)?
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Old Jan 24, 2011, 06:13 AM
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in desperation i tried brute-forcing the address

i get ACK on 0x74, and 0xF5, which matches your results, since the difference are bit7 - aka r/w

I don't belive the sensor is in 3.rd party mode, since it still works with the elogger, and that is not in line with the text in the "3.rd party mode doc"

That being said - i am going to look at 0x74 asap.
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Old Feb 15, 2011, 01:42 AM
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what difference between raw data and actual airspeed?

what difference between
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