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Old Mar 29, 2010, 08:56 AM
brdavis is offline
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I'm thinking of trying to use both of these with the LEGO NXT system. The problem here is it's a bit-banged system that I have no access to at a low level: in other words, I can pretty much just send and receive bytes from requested registers on the I2C device at a certain address. From that standpoint, it sounds like it might work... but I was curious, before risking it and buying one (or more) about a couple of things.

First, what's the slowest I2C speed folks have worked with this? There's a difference between the polling speed ("I'd like one read every second") and I2C speed ("this data needs to be sent at 400 kHz, or the sensor's going to time out because it thinks the master has forgotten about it"). IMS, the NXT FW runs a bit-banged I2C at 9600 bit/sec - what's the chances of this working?

Second, the NXT can power the sensor (the sensor ports supply 4.3V I think)... but they have a current limitation of around 20 mA. How much do these sensors draw? Will I need a separate power supply for them, or will they pull under, say, 30 mA at 4.3V?

I'm sure I have more question, but I think I need to crawl before I can even begin to think of walking here. Ultimately, the goal is to instrument a dropped payload from roughly 80,000'. Yes, I know they won't function at that low a pressure, but I'm having fun pushing off-the-shelf technology to silly limits... I mean, come on, it's LEGO . We've already used it for high-altitude balloon missions, including an autonomous parachute deployment during a 15 minute fall time (exciting to see on the accelerometer record... not a ride I'd like to take).

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Brian Davis
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