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  • To see more details in the graphs, sampling rate was changed to 1 sample / second, and values offset and scaled (except Volts):

    • Volts - light brown line: to scale
    • Satellites - green line: 2.0 + 0.1 * sats (0 satellites base line at 2.0, 5 sats at 2.5, 10 at 3.0)
    • GPS on - light blue line: on @ 2.9 (in 1st pic) and @ 3.1 (in 2nd pic), off @ 2.1 (off-pic)
    • Fix - dark red: 2.0 + 0.5 * fix (0 fix base line at 2.0, 1 fix at 2.5 and 2 fixes at 3.0).

    Power 'jumps around between 2.75..3.05 Volts. The longer the switched-off phase is, the slower satellites show. After a short - but still several minutes - break, many satellites are found quickly (5..6). Current was measured with a simple digital multi-meter at an average of 30 mA...

    On a 'really cold' start it took a while to get to level of fix = 1 even though some satellites were already found; and it takes quite a while to get to level of fix = 2, even though about the same number of satellites were detected much earlier. I did not look yet after what time the long and lat values become stable and useful. It could be worth-while to look into more recent generations of GPS modules that are much faster - not only in the interval of delivering sentences but also in start-up. A NEO 7M is still waiting on my desk to be 'broken in'. 7M does not only find 20..30% more satellites and quicker, it is more accurate, and has also an extended supply voltage range: Vcc 1.65..3.6V (vs 2.7..3.6V of 6M). The extended supply voltage may require to sacrifice less GPIO pins for just power supply. ;). How much current (mA) an STM32 pins can source is specified based on the voltage drop from Vcc...

    Note: The lower number of satellites found in this session compared to earlier session - 7..8 vs 9..12 - was due to a less optimal position of the GPS towards the open sky...

    2 Attachments

    • S11_Start_w_Scaling.png
    • S12_DetailsFixIncreased_w_Scalings.png

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