quick and dirty GPS

On a sunny day (26 Jul 2018 21:03:17 GMT) it happened ray carter wrote in :

Nice. Only restriction on using /dev/ttyUSB* is that if you plug in / out serial devices the kernel can renumber things.

Raspi has a real serial port on /dev/ttyAMA0 accessible via 2 GPIO pins. Many GPS modules come with logic level serial out. This stuff I wrote uses /dev/ttyAMA0

website needs updating... root@raspberrypi:~/compile/pantel/xgpspc# uptime 11:51:02 up 72 days, 4:19, 10 users, load average: 1.34, 1.52, 1.52

Stable :-)

Are the GPIO pins hot-pluggable, or will Nasty Things (*) happen if you connect/disconnect anything to them while the Pi is running?

(*) Either at the software or the hardware level.

On a sunny day (Fri, 27 Jul 2018 13:17:43 +0100) it happened "NY" wrote in :

No, not hot-pluggable. Very likely you will kill the chip if you try that. Static electricity, voltage levels above 3,3. V, wrong connection sequence, my remark was more for when you design a board. Also some electronics knowledge is required to interface to those pins.

There are also hats', but quite pricey:

No connection with them, I do see they copied the idea of my little sensor board with compass, and accelerometer ;-)

There is a whole team working on that boat navigation stuff, charts are available, there is also opencpn (I have that).

Probably much more. For me it is the fun of writing the code, understanding in depth how GPS etc works, and designing the hardware. I have an electronics background, so should not make those mistakes (killed one raspi nevertheless by shorting 5V to a 3.3V pin).

If you come more from the user perspective, then stay with the USB thing you have, I have modified some GPS modules by adding an ebay module for serial to USB too, works OK except for that renumbering every now and then.

If you are into navigation, steering a boat, way points etc, look into opencpn, and openplotter.

There's nothing in principle to prevent such hot plugging without damage, but there are some significant practical problems that need solving in order to give a guarantee in the worst case.

1) As another poster has pointed out, the voltage levels should be compatible. 2) The 0V pin must make contact first, followed by the power supply pin, and the signal pins must not make contact until power has been established on the other board. It's an unusual connector pair that would sequence the pins like that. 3) If two outputs are connected together, but they are at opposite logic states, it's possible that enough current will flow to damage one or the other pin. Thus, in software terms, you'd want to ensure that all pins that are going to be connected together have been configured to appropriate signal directions. If in any doubt, make the Pi's pins inputs before plugging up.

Dave

Alternatively a small resistor (1K will probably do) can be placed in the lines then even if two connected pins are both outputs for a short while they won't blow each other up. Lesson learned doing the Torch Z80 board - the data on the ports on both sides said on reset they were inputs, what it failed to mention was that between power up and reset they might be outputs for just long enough to break them, resistors solved the problem.

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Electrical theory says it doesn't make any difference if you contact ground or power first.

The obove can be seen on USB connectors, the power pins (both 0 and 5 volts) are longer so as to make contact first, but there is no distincion between both of them.

Wher terminals are concerned, it takes two to tango

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always run out of other people's money. It's quite a characteristic of them" 

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In fact, anyone can define ground to be exactly which voltage level they want.

--
RoRo

Most theoretical descriptions only hold as long as the simplifying assumptions made in their formulation do. Even if your circuit is totally isolated from anything else it can be any potential whatsoever and it always has a certain capacity against its surroundings. The ground plane typically is the most robust part to take the initial inrush.

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