New GPS Project Advice...

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jamhaley
 
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New GPS Project Advice...

Post by jamhaley »

I'm planning a very small handheld GPS with the following components and have some questions, Ultimate GPS module, Arduino Micro & either Sharp Memory display or 1.3" 128 x 64 OLED display. I'm trying to keep it as small as possible.

1. I could power it with a 9V Lion, but what about stacking two 3.7V cell phone batteries and wiring them in series? That point is space saving: 9V is 16mm thick and 2 cell phone batts are 10mm. (recharging them will probably be interesting???)

2. I've read that GPS antennas experience signal loss if covered by plastic (cases). I've experimented with acrylic and polycarbonate covering the GPS module with the MiniGPS tool running and can't see any loss of SNR...what'd'ya think????

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adafruit_support_mike
 
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Re: New GPS Project Advice...

Post by adafruit_support_mike »

1) The LiPo packs will give you better battery life, but you're right that charging them will be interesting. Your major options are to use a preassembled multi-cell LiPo pack and the charger appropriate to that, or to put regular LiPo packs in series and charge them separately,

We have a couple of LiPo chargers that handle charge/load balancing automatically, and theoretically you could put those in series, but you'd have to be careful about connecting the power to those when you charge.. if the power supplies to the chargers share a common GND, things could get 'splodey.

2) Figuring radio signal strength is like painting in the dark.. we don't have senses that can observe the signals of interest. Radio waves fall on the same electromagnetic spectrum as light, and acrylic has a higher index of refraction than glass, so there is some interaction between the signals and the materials. If your setup doesn't cause any problems, go for it.

jamhaley
 
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Re: New GPS Project Advice...

Post by jamhaley »

Thanks, that's a big help. Regarding power, I found some 3.7V 10440 Lithium Ion batteries (same dimensions as AAA) and they are 600 mAh each. The dimensions are good, 10mm diameter, vs 16-17mm for 9V. Chargers are readily available. So, 3 in series = 11.1 volts...should work, Right??

jamhaley
 
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Re: New GPS Project Advice...

Post by jamhaley »

Oh, and re: GPS signal loss (due to plastic case)...the last one I built had 1/8" Lexan (polycarbonate) over the GPS breakout and I took it on a ship and did a side by side test with a high-end Kinematic + differential GPS (Portable Pilot Unit) and the the performance was practically identical with regard to "speed over ground" and "course over ground" which are the critical parameters in ship piloting which is my application, and so, it appears "it ain't broke, so point in fixin' it"!!!

Thanks again for your patience...JH

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astronomerdave
 
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Re: New GPS Project Advice...

Post by astronomerdave »

Last year I built exactly what you are describing. I used the small Otterbox #1000 (https://www.adafruit.com/products/340) and it worked great.

jamhaley
 
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Re: New GPS Project Advice...

Post by jamhaley »

Thanks. What I need now is a routine to average speed over 5-10 seconds. I'm too new to code to know where to start. I've got it working using much of the "leo_parsing" example. Does anyone have a routine to smooth out speed by averaging it over 5-10 seconds?

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adafruit_support_mike
 
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Re: New GPS Project Advice...

Post by adafruit_support_mike »

A weighted running average should work:

Code: Select all

position = ((position * 9) + newReading) / 10;
Giving the previous values more weight makes the output less sensitive to noise, but also makes the output less responsive to real changes. Giving the previous values less weight makes the output more responsive, but allows more noise to sneak through. Play with the values until you find the balance that works for your application.

jamhaley
 
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Re: New GPS Project Advice...

Post by jamhaley »

Right. I'm using GPS on ships and boats where speed changes relatively slowly, and most systems average speed over the past 5-10 seconds. I lack the coding expertise...any suggestion where I might find some example code that can accomplish this???


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