Low power usb ports?

alisdair4

alisdair4

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midnightdrifter.net
I have been experimenting with replacing the boat laptop (2005 vintage, 13") with a more modern netbook (Samsung, 10", 2010) as the laptop is on its last legs. However, althought the laptop runs all of the inputs (GPS, AIS and NAVTEX, through USB to Serial Ports) which I want through a single lead to an unpowered 4-port hub, the Netbook will only recognise one input. Am I correct in thinking that netbooks have a less powerful (ie, lower amperage) USB port, and thus the port will not power the hub? Thus, the solution will be a powered hub of some sort? (In case you are wondering "why doesn't he just try it", I am not collocated with the boat!).
 
It depends on how the laptop manufacture chose to implement the standard with regard to USB power. There are a number of legitimate options.
http://en.wikipedia.org/wiki/USB#Power

Rather than use 4 off USB/serial bridges + hub you could consider a 4 way USB/serial bridge such as this;
http://www.ebay.co.uk/itm/Newlink-QUAD-USB-2-0-Serial-RS232-Adapter-4-Port-/200573327284?pt=UK_Computing_Parallel_Serial_PS_2&hash=item2eb31a17b4

I use this one although I can't remember where I bought it. It runs happily on my Toshiba Netbook and provides me with AIS, GPS, NAVTEX and I'll add a link to the autopilot soon.

The downside is that all 4 ports are RS232, so you can't have an RS232 and RS485/422 mix. (NEMA 0183 uses RS485/422 although many people cobble it into a RS232 port.)
 
alisdair4 said:
Sadly, I only have one 240v socket coming off my invertor (which is there for the laptop). I guess I could put a double adapter on this - given that a hub doesn't draw too much power?
Click to expand...

Going up to 240v and then back down again is a heck of an inefficient way of getting a low voltage DC supply. It should be reasonably straightforward to find a 12V power supply for the hub ... and for the laptop, for that matter.
 
I tried 2 different ones from ebay inc a powered one. none any good.
Then good old amazon
Konig 4 Port USB 2.0 Hub with Cord - Black


It works just as it should linking
gps & wifi booster dongles, phone usb teathering ( or camera usb) cable, AIS antenna
 
John,

I'll have a look a this - may be a neater solution. Thanks.

JohnGC said:
It depends on how the laptop manufacture chose to implement the standard with regard to USB power. There are a number of legitimate options.
http://en.wikipedia.org/wiki/USB#Power

Rather than use 4 off USB/serial bridges + hub you could consider a 4 way USB/serial bridge such as this;
http://www.ebay.co.uk/itm/Newlink-QUAD-USB-2-0-Serial-RS232-Adapter-4-Port-/200573327284?pt=UK_Computing_Parallel_Serial_PS_2&hash=item2eb31a17b4

I use this one although I can't remember where I bought it. It runs happily on my Toshiba Netbook and provides me with AIS, GPS, NAVTEX and I'll add a link to the autopilot soon.

The downside is that all 4 ports are RS232, so you can't have an RS232 and RS485/422 mix. (NEMA 0183 uses RS485/422 although many people cobble it into a RS232 port.)
Click to expand...
 
alisdair4 said:
Sadly, I only have one 240v socket coming off my invertor (which is there for the laptop). I guess I could put a double adapter on this - given that a hub doesn't draw too much power?
Click to expand...

No way should you be using an inverter to power a laptop, get a 12V adaptor.

A powered USB hub will need 5V, often via a mini-USB socket, so you should be able to use an iPad 12V to USB charger (which gives 2A), like this: http://www.amazon.co.uk/exec/obidos/ASIN/B006SU0SX0/dolcetto-21

Regarding the number of ports, I would advise using a pair of dual port leads, that way if there is a problem you have some options. This is currently the best available, having COM port retention and FTDI chipset:
http://www.amazon.co.uk/exec/obidos/ASIN/B0055CRAF6/dolcetto-21
 
Last edited:
nigelmercier said:
No way should you be using an inverter to power a laptop, get a 12V adaptor.

A powered USB hub will need 5V, often via a mini-USB socket, so you should be able to use an iPad 12V to USB charger (which gives 2A), like this: http://www.amazon.co.uk/exec/obidos/ASIN/B006SU0SX0/dolcetto-21

Regarding the number of ports, I would advise using a pair of dual port leads, that way if there is a problem you have some options. This is currently the best available, having COM port retention and FTDI chipset:
http://www.amazon.co.uk/exec/obidos/ASIN/B0055CRAF6/dolcetto-21
Click to expand...

I have similar to this
http://www.maplin.co.uk/12v-auto-vo...r-with-usb-socket-1a--12-charging-tips-614040
 
As per Nigel's post above - I would look for a Serial<->USB adapter that has the FTDI chipset in it (for better reliability and compatibilty)..

To save on the mass of cables I just went for one of these by Startech (ICUSB2324X). Four serial ports, FTDI chipset, COM port retention and no external power requirements.
http://www.amazon.co.uk/StarTech-com-Mountable-Serial-Adapter-Retention/dp/B001OFNLTM#productDetails
It works happily on a netbook with concurrent input from AIS at 38400, NMEA at 4800, Seatalk (via NMEA converter) at 4800 and a dial out Satellite phone connection at 9600bps.
 
nigelmercier said:
Regarding the number of ports, I would advise using a pair of dual port leads, that way if there is a problem you have some options. This is currently the best available, having COM port retention and FTDI chipset:
http://www.amazon.co.uk/exec/obidos/ASIN/B0055CRAF6
Click to expand...

I bought one of these. In a "normal" application you wouldn't have notice but they don't handle parity errors correctly. For the application here if everything is working correctly they should be fine but if there is a fault it will be incorrectly flagged and if you're doing anything like I was with seatalk where you need an accurate reflection of the parity bit, they're useless. And startech's tech support were not helpful.
 
laika said:
I bought one of these. In a "normal" application you wouldn't have notice but they don't handle parity errors correctly. For the application here if everything is working correctly they should be fine but if there is a fault it will be incorrectly flagged and if you're doing anything like I was with seatalk where you need an accurate reflection of the parity bit, they're useless. And startech's tech support were not helpful.
Click to expand...
They are 8-bit ports, for SeaTalk you need true 9-bits, not 8+1
 
nigelmercier said:
They are 8-bit ports, for SeaTalk you need true 9-bits, not 8+1
Click to expand...

The 9th bit is reflected in the parity bit of a normal UART. If you invert the seatalk signal (using the board in the Thomas knauf site or the improved one you once posted here) and feed it into a serial interface with SPACE parity set, a parity "error" indicates that the command bit is set. This works with a "proper" serial interface. I also have a no-name FTDI serial to USB adaptor which it works perfectly with. The startech dual one double reports the error, reporting a subsequent (correct) byte as erroneous. Which prompted me to artificially generate other types of parity error which it also has problems with. Provided test case to Startech. Several months of the poor front line support guy chasing up the backroom people wit hno reply. Eventually after some mails to their management they acknowledged there was a fault accross many of their products. They were going to send me a replacement when they'd fixed the problem. Still waiting.
 
USB was 5V and 0.5A in it's initial design. That still goes and will charge/drive early and small consumption devices like iPhone 3. Many USB devices take no power from the port and only transmit data.

Later, with greater demands like iPad etc. the standard went up to 1A and 2,1A - still at 5V. To cope with all the market even saw power bank devices (ie. external batteries), to support the biult-in power source.
Multi-port USB power supplies, also running off 12V, produce ~2A and share it on several outputs. hence a 4-port device will supply 0.5A to each port.

In theory, and almost in practise, a 2.1A charger will reduce charging time to 25% of a 0.5A charger. The device's ability to utilize the higher charge decides if practise it will take longer than theory.
 
nigelmercier said:
But with space parity, does the receiver not ignore it?
Click to expand...

With apologies that I've sent this completely off topic (and will shut up after this :-)...with SPACE parity, the "parity" (9th if data transmissoin is 8 bit) bit is set to 0 on transmit and 0 is expected on receive. If it's 1, a parity error should be generated. Receiving software can ignore that or use it as it sees fit. From *nix user space it was the only way I could think of to access the seatalk command bit. Works fine, but not with that startech usb to serial cable (it has the same issue with "normal" even/odd parity as it does with mark and space).

You can *generate* seatalk by flipping to MARK parity before transmitting a command byte, then flipping it back to SPACE afterwards.
Given timing issues for collision avoidance though, I think seatalk *transmission* is probably best not done from a simple user space program designed for end users on a multiuser OS.
 
alisdair4 said:
I have been experimenting with replacing the boat laptop (2005 vintage, 13") with a more modern netbook (Samsung, 10", 2010) as the laptop is on its last legs. However, althought the laptop runs all of the inputs (GPS, AIS and NAVTEX, through USB to Serial Ports) which I want through a single lead to an unpowered 4-port hub, the Netbook will only recognise one input. Am I correct in thinking that netbooks have a less powerful (ie, lower amperage) USB port, and thus the port will not power the hub? Thus, the solution will be a powered hub of some sort? (In case you are wondering "why doesn't he just try it", I am not collocated with the boat!).
Click to expand...

While most of the replies are valid they address the symptoms. I would think that the issue possibly a configuration issue. Assuming you are using Windows? Windows really does not handle usb/serial conversation well. I recently had similar issues on a Hot netbook which in the end turned out to be a windows plug and play problem.
 
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