In Car Use Issues/Experiences


#1

Hi,

I would like to build a custom board with available commercial modules in order to make a car pc. I have some questions in advance, I will be glad if you share your experiences:

  • How can I power on the system automatically? Is there a such pins like “Run” pin in rapsberry pi? What I want is powering on the system when ignition cable is high.

  • How can I match car FM antenna with antenna of dragonboard?

  • Any recommendation for fuse usage?

  • Is GPS antenna reception good? Do you recommend any passive antenna?

  • Is anybody experienced powering from battery, is there any issue?

Thanks


#2

By default it will power on when connected so you could use a simple switched live… of course you may have to be careful not to turn off the ignition whilst the DB410C is writing to its eMMC (or design your software so that the critical partitions can be mounted read-only).

There might be scope for more exotic approach but this will require carefully timed management of the power buttons (power button can distringuish short press, 3s press and 10s press).

FM_RX_ANT is routed to pin 15 of the analog audio connector… other than that I’m afraid I have no clue (I also noted that the hardware manual says that FM radio “an optional addition that has not been tested and is not officially supported”). I’m afraid you might just have to experiment here.

You could also try interfacing one of the RTL-SDR USB dongles since that will allow you a greater range of signals and some future proofing for jurisdictions where FM will be turned off soon. RTL-SDR is a family of cheap TV receiver devices that can also receive DAB and FM signals (I’m afraid getting these running is out-of-scope for this forum but the RTL-SDR community might be able to help).

Board should not be drawing more than 24W. In fact IIRC 17W of this budget is for powering downstream things either via USB or via the LS connector. In other words you can use quite a small fuse; 2A is a sane default but you could probably tighten things further if you want to.

I don’t have any particular recommendation but you will need an external antenna, the PCB antena will not be sensitive enough.

The voltage input for this board ranges from 6.5v to 18v so there should be no point when the car voltage is running out of spec (car looms can are 12v nominally but can reach up to about 15v, is that right?).

I’m afraid I don’t know the power draw figures that would let you calculate how long you can run the board for on a battery.


#3

Car has 12V rail and 12V ignition logic level. Normal 12V direct battery connection is always available whether the car is on or off. So even if I shut the system down there should be a way to boot it up automatically with ignition signal. One way may be using a microcontroller. Is there a easier solution?

Still so many people are suing FM radio since so many old cars are still in the market. I dont want to use any usb device because I dont want to sacrifice usb bandwith for anything. I may use usb for android auto, so usb bandwidth is very precious.

My main concern is can I directly connect it to fm cable? I have no experience on it maybe signal has to be amplified or vice versa.[quote=“danielt, post:2, topic:2107”]
Any recommendation for fuse usage?

Board should not be drawing more than 24W. In fact IIRC 17W of this budget is for powering downstream things either via USB or via the LS connector. In other words you can use quite a small fuse; 2A is a sane default but you could probably tighten things further if you want to.
[/quote]
I am afraid of it if there will be short circuit on the pcb it can draw so many current from the battery and burn something. If we include the current consumption for lcd and usb , do you think that 2A is too low?[quote=“danielt, post:2, topic:2107”]
Is anybody experienced powering from battery, is there any issue?

The voltage input for this board ranges from 6.5v to 18v so there should be no point when the car voltage is running out of spec (car looms can are 12v nominally but can reach up to about 15v, is that right?).

I’m afraid I don’t know the power draw figures that would let you calculate how long you can run the board for on a battery.
[/quote]

I think using external battery is quite dangerous as we see from samsung example. Especially in the car it can be quite dangerous, I give up from this idea.

Many thanks for your answers. I am looking for your replies.


#4

[mbt28] mbt28 http://discuss.96boards.org/u/mbt28
June 19

danielt:

How can I power on the system automatically? Is there a such pins
like "Run" pin in rapsberry pi? What I want is powering on the
system when ignition cable is high.

By default it will power on when connected so you could use a simple
switched live... of course you may have to be careful not to turn
off the ignition whilst the DB410C is writing to its eMMC (or design
your software so that the critical partitions can be mounted read-only).

There might be scope for more exotic approach but this will require
carefully timed management of the power buttons (power button can
distringuish short press, 3s press and 10s press).

Car has 12V rail and 12V ignition logic level. Normal 12V direct battery
connection is always available whether the car is on or off. So even if
I shut the system down there should be a way to boot it up automatically
with ignition signal. One way may be using a microcontroller. Is there a
easier solution?

Surely you have a choice about whether you use a switched live or a
permanent live. However if you want to use both to get a better user
experience (controlling ICE with a switched live is kinda nasty) then I
think you will probably need some kind of micro-controller to manage things.

How can I match car FM antenna with antenna of dragonboard?

FM_RX_ANT is routed to pin 15 of the analog audio connector... other
than that I'm afraid I have no clue (I also noted that the hardware
manual says that FM radio "an optional addition that has not been
tested and is not officially supported"). I'm afraid you might just
have to experiment here.

Still so many people are suing FM radio since so many old cars are still
in the market. I dont want to use any usb device because I dont want to
sacrifice usb bandwith for anything. I may use usb for android auto, so
usb bandwidth is very precious.

My main concern is can I directly connect it to fm cable? I have no
experience on it maybe signal has to be amplified or vice versa.

I’m afraid I can’t add any more than I’ve already said… it comes out
on pin 15 and I don’t know what you need to connect to it.

Any recommendation for fuse usage?

Board should not be drawing more than 24W. In fact IIRC 17W of this
budget is for powering downstream things either via USB or via the
LS connector. In other words you can use quite a small fuse; 2A is a
sane default but you could probably tighten things further if you
want to.

I am afraid of it if there will be short circuit on the pcb it can draw
so many current from the battery and burn something. If we include the
current consumption for lcd and usb , do you think that 2A is too low?
2A is plenty for board and USB. Its probably OK for LCD too but that
depends on your panel.


#5

Is it possible to reprogram PM8916 for a specific use in the car? If I put the system suspend mode by software how can I wake it up?

What I want:
Ignition on -> board wake up (if it is off power on)
Ingition off -> board suspend
Ignition off + low battery level -> board shutdown


#6

Hi,

Can you please share me your powering on powering off solutions for in car use? I know some people were using for car pc.

Thank you.