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Forum Index : Microcontroller and PC projects : VK16E GPS module
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| robert.rozee Guru  Joined: 31/12/2012 Location: New ZealandPosts: 2442 |
has anyone found that their VK16E module stops outputting NMEA data after exactly 128 minutes? i am currently experimenting with sending a restart command to get around this. the problem cropped up with the module used in a base station that sits unattended. cheers, rob :-) |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
I left mine running for 24 hours and no sign of giving up. There are some power saving modes that might be the cause. Jim VK7JH MMedit |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2442 |
well, i left mine running for 4 hours after sending a cold reset command, and it didn't miss a beat. so i guess the options are either (a) it was overheating in the clear plastic jar sitting out in the sun and the time just happened to be 128 minutes, or, (b) an earlier run of SiRFdemo had set up some strange configuration, or, (c) the 1200uF power supply filter capacitor i've now added did something to prevent a hiccup. btw, below is a photo of my GPS base station. i showed it to a friend who used to work in the industry and he couldn't help laughing. the GPS module is a VK16E, while the transceiver is a us$5 HC-12 clone from ebay (430MHz, 500m range, 9600 baud serial data). power is 3xAA cells, no regulator, good for about 50 hours. 
if anyone is interested, i'll upload a copy of the delphi (windows) test application i've written to view and log the data. once i've got a feel for the behaviour of the equipment, i'll be moving over to a micromite-powered mobile station (the base station will remain as is, just a transceiver and GPS module connected directly together). cheers, rob :-) |
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| HankR Senior Member  Joined: 02/01/2015 Location: United StatesPosts: 209 |
Rob, Was it apparent what aspect of your rig he found funny? Did he seem impressed by it? Small size, low current, low total cost, and so on? Hank |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2442 |
all of the above - a GPS base station used to be somewhat more substantial, whereas mine could just about fit into a matchbox (excluding the battery). to a large extent it is the progress of technology, with the SiRF chipset being a bit or a revolution to the industry as far as i can tell. meanwhile, the HC-12 uses a SiLabs transceiver-on-a-chip to shrink the radio down to less than a square inch of board space. cheers, rob :-) |
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MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
A setup like that would cost over 100US$ about 1-2 years ago. Put it in a nice box and it would have cost 200US$. Maybe it is a laugh how unbelievable that would be to make for 20US$ now. I am designing something similar but then with a WiFi module to transmit the data to a server. Microblocks. Build with logic. |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2442 |
now that raises an interesting set of questions: 1. with differential GPS, how far can one have between the remote station and base station? hundreds of metres without a doubt, but what about 10's of kilometres? with my own experiments, i'm only interested in a few hundred metres, which the HC-12 provides nicely. 2. lets say your base station sits outside and is powered by a solar panel, transmits to a nearby wireless network, and the correction data is available via a web interface. could that data then be used by a GPS enabled cellphone (via cellular data connection) to produce very accurate fixes? 3. what if a city decided to provide such GPS base stations on a regular grid, perhaps atop traffic lights, street lamps? what useful applications are there for this sort of coverage? cheers, rob :-) |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
My goal is to use it in a vehicle and use a smartphone with WiFi internet sharing enabled to be the gateway to internet. This will allow drivers to use their phones account for GPS data transmissions (Machine to Machine communications is often 10-100x more expensive) Using a smartphone for GPS is also not working very well. They get hot and can even overheat, they have weaker GPS reception and most importantly they run out of battery very quickly. Using a dedicated GPS with WiFi solves all of those problems as long as it can be fixed and powered like in a vehicle. It will need to buffer GPS info when there is no WiFi available (FRAM/SD) and can also use WiFi access points, like one at home, office or depot. I wil do at least a run of 100 of them once development/testing is finished. Microblocks. Build with logic. |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2442 |
i'm seeing around 30mA for the VK16E module, which i'm guessing is fairly typical. enough to put a fair dent in the battery life of the average smart phone. i'm guessing the manufacturers only budgeted on the GPS being run intermittently. btw, for those who asked, here is the windows application i've been using for testing: 2015-12-21_152252_GPS.zip |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2442 |
well folks, it seems that differential GPS is a bit of a bust. i'm currently waiting on the arrival of a couple more HC-12 transciever modules so i can set up a second base station outside to do some 24-hour data collecting, but i am not expecting to see great results. see this article on the subject: http://archive.oreilly.com/pub/a/wireless/2000/12/29/two_gps.html essentially, the problem is that there is no way two GPS receivers sitting even side-by-side can be guaranteed to use the same set of satellites to get a fix. this means the 'meanderings' of each GPS receiver's location will be largely independant and uncorrelated to that of the other. for differential GPS to work in a useful way one requires availability of individual satellite-to-station ranges (raw data), which the cheap (ebay) SiRF3 based modules don't output. and even if this data was available (U-blox modules can output the raw data), making use of it in real-time requires far more computing power than is available from a micromite; none of the cheap SiRF3 or U-blox modules provide the facility to have range data fed back into them to do the corrections themselves internally. the only other solution would be to figure out how to synchronize the set of satellites the two GPS modules used in a fix, essentially adjusting the almanac data held in the GPS modules so that non-shared satellites are excluded. this would be an extremely messy kludge. on the plus side, i'm now looking at using ultrasonic rangefinding as an alternative - not the conventional reflected echo variety, but rather sending a pulse between two stations and timing the flight in first one direction (A->B) then the other (B->A). not relying upon reflection significantly improves performance. use of HC-12 modules will enable both sending results back and forth as well as synchronizing clocks. two base stations a known distance apart plus a movable survey station should allow sub centimetre x,y coordinate location. (40kHz sound travelling at approximately 330m/s = 8mm resolution counting cycles. speed of sound in air, while dependant on temperature, is well defined. measurement in both directions cancels out any errors due to wind speed) i'd be interested in feedback on this idea. cheers, rob :-) |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
Rob, I have read that WiFi AP's can be used to triangulate a position. It was used on some convention i went to long time ago, You got a badge with a RF transceiver and they could map each person's whereabouts and see where and how people walked. I forgot the name, it was open source. I will try to find it. EDIT: Got it. Info can be found here: http://www.openbeacon.org/BruCON_2011 Microblocks. Build with logic. |
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palcal Guru Joined: 12/10/2011 Location: AustraliaPosts: 1993 |
Try looking at Ultrasonic Anemometers there are some DIY articles on the web, may give you some ideas. Paul. "It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all" |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2442 |
MicroBlocks: the linked page made for an interesting read. while RF time-of-flight could indeed be used, it poses a whole set of complex problems that are well above my pay-grade. one really does need to do pico-second timing to create either RF or laser rangefinders (though there are ways of doing this indirectly) at which point it becomes easier to revisit differential GPS solutions. palcal: looks like the right starting point! have just had a look at a couple of solutions folks have come up with (googled <homemade ultrasonic anemometer>) and the electronics looks encouragingly simple. i have two sets of transducers on the way from ebay china and will need to do some trials when they arrive. cheers, rob :-) |
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