6 ms·

Looks like pretty standard WSN tech. Some points of critique: - Range: 50 square miles? That would imply a range of r=4 miles, which is pretty impressive. Is t

by inoop 12y ago

Looks like pretty standard WSN tech. Some points of critique: - Range: 50 square miles? That would imply a range of r=4 miles, which is pretty impressive. Is this single hop, or are they 'cheating' by implying a multi-hop network? The best I've seen is >1km on an Australian deployment where the base station was on a hill and the nodes were deployed on a lake, and this was using an nrf905 on the 915 MHZ band with a whip antenna iirc. - Power consumption: 0.026mA. Amps is a measure for current, not energy? I can send 10 bytes at near-zero average amps as long as I do it only once per millennium. This number is completely meaningless without a time scale. They should just report mJ if they want to talk about the energy consumed in a single operation. - 765 days life time. Again, they are not reporting the full story here: what is the size of the battery? What type of battery? Is this estimated, or measured? These nodes typically use MSP430's and may have a very, very low sleep current (e.g. ~8uA for a tmote). However, the numbers quoted by the manufacturer are often averages, and there may be significant differences between nodes (http://www.cse.msu.edu/~glxing/docs/ipsn13-Nemo.pdf http://www.cse.msu.edu/~glxing/docs/ipsn13-Nemo.pdf) Two years is a very typical life-time for sensor nodes. However, you can only get that with very, very low data rates (e.g. one packet every minute). If you're doing multi-hop, nodes close to the sink (bridge) will drain faster as they have to relay not only their own data, but that of nodes down the routing tree as well. So, you might end up with a situation where the life-time of the network is much lower than that of an individual node. - Nitpicking, but one day is not typical at all for cellular. Sure, your phone only lasts a day on a charge, but that is mostly due to to the main SoC and display. If you look at the modem in isolation, most of the energy is spent in energy tails, which you could cut down considerably on a network that supports fast dormancy. If you don't care too much about latency (i.e. you want your nodes to upload data only once per so-many hours or even days), you can easily go a week between battery swaps.

vacri 12y ago
They should just report mJ if they want to talk about the energy consumed in a single operation. Nah, not really. When your battery is rated in "amp-hours" and you're being extremely tight with your radio, turning it on and off as necessary, it's fine to measure it in mA - the time unit is 'silent'. Radio was on for 10 seconds? Take 10x0.026 off the amp-hour stored in the battery. My last workplace dealt in agricultural telemetry based off solar-panel charged lead-acid batteries, rated in amp-hours. Amp-hours are similar to units of energy, but are subtly different - really they are actually measuring storage of electrical charge, which is not the same thing: http://en.wikipedia.org/wiki/Ampere-hour http://en.wikipedia.org/wiki/Ampere-hour They even had to put unicode support into the software configuration tool, because the boss was very clear that the proper unit for amp-hour is A·h, not Ah.
- leoedin 12y ago
  Without a defined voltage, mA and mAh are meaningless. We could assume that they used a 3.7V lithium battery because that tends to be the case with this type of technology, but it isn't stated anywhere. The criticism is completely valid.
  - vacri 12y ago
    In theory, there is no difference between theory and practice. In practice, there is. The criticism is not completely valid - I've just given you an example of where, in industry, it's used in the same manner as originally mentioned. You can shout at the wind that it's blowing wrong, but it's still going to blow - reporting power consumption in mA is used in industry, so it's useful to report. Anyway, batteries come in standard voltage ratings - 1.5, 3, 9, 12, 24, and a host more. You select a battery that has the same rating as your electrical tool's requirements, so the voltage is already known, and the charge is delivered within the tolerance range of that voltage rating. And whether you're working in amp-hours or joules, you still need to know the voltage rating of your power source, so you will have this information at hand - it's utter nonsense to think that the only rating you need to know would be joules, or that the voltage for a given model of battery would be mysteriously unknown (and even if it were, trivially solvable with a multimeter, unlike amp-hour or joule).
    - leoedin 12y ago
      Your comments suggest to me that you're not a practising electronics engineer and don't have much experience with digital electronics design. You've demonstrated confused thinking about the meaning of units and complete ignorance of digital design processes. > In theory, there is no difference between theory and practice. In practice, there is. I've read this a few times and I'm still at a loss as to what you're trying to say. > reporting power consumption in mA is used in industry, so it's useful to report. The example you gave is of a different industry. This device is a digital communications module, and so I'd expect information to be provided in a form which is useful for digital electronics desginers to use. The data provided by the Helium people is not sufficient to understand the power use of the radio. I agree that reporting current draw during transmission is useful, but it is only one of a number of figures required to allow an accurate assessment of the radio's capabilities and power consumption. The electronics industry has standardised on multi-page datasheets to provide key information on device functionality. There's a reason for this. Ultimately the information given about the device is not sufficient to allow a design engineer to make an accurate assessment of its capabilities.
deleted 12y ago
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by inoop 12y ago

vacri 12y ago

They should just report mJ if they want to talk about the energy consumed in a single operation. Nah, not really. When your battery is rated in "amp-hours" and you're being extremely tight with your radio, turning it on and off as necessary, it's fine to measure it in mA - the time unit is 'silent'. Radio was on for 10 seconds? Take 10x0.026 off the amp-hour stored in the battery. My last workplace dealt in agricultural telemetry based off solar-panel charged lead-acid batteries, rated in amp-hours. Amp-hours are similar to units of energy, but are subtly different - really they are actually measuring storage of electrical charge, which is not the same thing: http://en.wikipedia.org/wiki/Ampere-hour http://en.wikipedia.org/wiki/Ampere-hour They even had to put unicode support into the software configuration tool, because the boss was very clear that the proper unit for amp-hour is A·h, not Ah.

leoedin 12y ago
Without a defined voltage, mA and mAh are meaningless. We could assume that they used a 3.7V lithium battery because that tends to be the case with this type of technology, but it isn't stated anywhere. The criticism is completely valid.
- vacri 12y ago
  In theory, there is no difference between theory and practice. In practice, there is. The criticism is not completely valid - I've just given you an example of where, in industry, it's used in the same manner as originally mentioned. You can shout at the wind that it's blowing wrong, but it's still going to blow - reporting power consumption in mA is used in industry, so it's useful to report. Anyway, batteries come in standard voltage ratings - 1.5, 3, 9, 12, 24, and a host more. You select a battery that has the same rating as your electrical tool's requirements, so the voltage is already known, and the charge is delivered within the tolerance range of that voltage rating. And whether you're working in amp-hours or joules, you still need to know the voltage rating of your power source, so you will have this information at hand - it's utter nonsense to think that the only rating you need to know would be joules, or that the voltage for a given model of battery would be mysteriously unknown (and even if it were, trivially solvable with a multimeter, unlike amp-hour or joule).
  - leoedin 12y ago
    Your comments suggest to me that you're not a practising electronics engineer and don't have much experience with digital electronics design. You've demonstrated confused thinking about the meaning of units and complete ignorance of digital design processes. > In theory, there is no difference between theory and practice. In practice, there is. I've read this a few times and I'm still at a loss as to what you're trying to say. > reporting power consumption in mA is used in industry, so it's useful to report. The example you gave is of a different industry. This device is a digital communications module, and so I'd expect information to be provided in a form which is useful for digital electronics desginers to use. The data provided by the Helium people is not sufficient to understand the power use of the radio. I agree that reporting current draw during transmission is useful, but it is only one of a number of figures required to allow an accurate assessment of the radio's capabilities and power consumption. The electronics industry has standardised on multi-page datasheets to provide key information on device functionality. There's a reason for this. Ultimately the information given about the device is not sufficient to allow a design engineer to make an accurate assessment of its capabilities.

deleted 12y ago

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