My open source GPS logger. Request for comments - Page 1
Forum section: electronics / general

author: krakrukra
author_rank: Newbie
timestamp: November 02, 2018, 04:33:51 pm
content: Hello, I have designed this OSHW GPS data logger:https://github.com/krakrukra/SD_TrackI did some tests and it seems to be OK. So I decided to get some feedbackfrom other people, such as:what do you think of it?what functionality you think should be added?what things can be implemented in a better way?would you buy a thing like this for 40-50$ ?And in general, any feedback would be appreciated.

author: Twoflower
author_rank: Frequent Contributor
timestamp: November 02, 2018, 05:15:13 pm
content: Looks nice. But I just checked the photos. Two comments to your specific setup:1. Nice waterproof housing. But the switch renders that useless ;-)2. I would place the GPSr on the other side of the PCB or put the battery below the PCB. The latter is maybe a better solution because the external mounting holes of the housing. This way only the housing is in the way between the receiver and the satellites. Your design adds the battery to the path. You probably not gain much, but still that might be the missing dBm under critical conditions.Functions that might be potential selling points:1. Probably a Bluetooth/WLAN way to get the track downloaded from the device. To safe energy the WLAN might be activated only at specific coordinates and if a minimum track length is stored. Maybe also a automatic try to store on a FTP/SMB server.2. A buzzer that goes off if close to stored coordinates. This one might be easy to implement.

author: krakrukra
author_rank: Newbie
timestamp: November 02, 2018, 05:46:33 pm
content: Well, the antenna for the receiver is actiually on the bottom layer. This implies that signal comes from the satellites,reflects off the ground, and then goes to the antenna just through the enclosure. That is the idea behind component placement.The mounting holes are not actiually used there. The case just comes like this from the manufacturer.

author: Twoflower
author_rank: Frequent Contributor
timestamp: November 02, 2018, 05:57:13 pm
content: I should have checked a bit more about your project before commenting. Especially about the antennae. My impression was that the GPSr (the SIM28) contain the antennae. Still I was a bit wondering about the case of the SIM28 and haven't read the next line of the BOM.txt.Note to myself: Spend more time to check all information before commenting.

author: awallin
author_rank: Frequent Contributor
timestamp: November 03, 2018, 07:46:44 am
content: What battery life do you get with your box?The basic sports-watches will log position for 4-5 hours (marathon) easily.Some triathlon/'adventure' devices have some battery-saver mode and can log position for maybe 12 hours.The numbers are similar-ish (I think) for bike-computers - they should have a bit more space for the battery but they also have large screens..If you can config your device for something significantly longer in terms of battery-life it might be interesting for longer bike-trips or hiking etc.For this use-case a display that shows it is working, and maybe coordinates/velocity/heading would be nice..

author: krakrukra
author_rank: Newbie
timestamp: November 03, 2018, 08:24:52 am
content: The battery is 3000mAh, and device works with battery voltage above 2.9-3V. So after full charge let's say 0.9 of capacity is used = 2700mAh.Current consumption while tracking is a little below 40mA, while in sleepmode below 1mA. 2700mAh / 40 mA = 67.5h of continuous tracking,at least based on the calculations. Though I was not testing battery life this way, I was testing it together with sleepmodes to see if it lasts for acouple of weeks under my car and it did. I have upgraded the battery from 1800mAh to 3000mAh since then and have not tested these yet.

author: JPL
author_rank: Newbie
timestamp: November 12, 2018, 11:15:26 am
content: A coup of years ago, I have made this 10 MHz GPS frequency standard

author: @rt
author_rank: Super Contributor
timestamp: December 02, 2018, 03:37:02 am
content: Quote from: krakrukra on November 02, 2018, 05:46:33 pmThat sounds like a problem. Does any commercial GPS implement an antenna that way?

author: krakrukra
author_rank: Newbie
timestamp: December 02, 2018, 08:01:05 am
content: Yes, I actiually got this idea from TKSTAR TK905, these are sold on aliexpress. They have receiver on top and antenna on the bottom.There really is no better place for it, since the device is supposed to be mounted below the car magnetically on a metal surface.So antenna either faces the ground or the hull.

author: @rt
author_rank: Super Contributor
timestamp: December 26, 2018, 02:29:37 pm
content: The Garmin Montana, and Oregon handheld (hiking) GPS units do it because the display is almost the size of the enclosure.I wonder how that affects the radiation pattern of a patch antenna.