How I build my C4 Carputer

[rooted]

Is that steel mesh?

[joerg]

No, it's anodized aluminium.

[rooted]

It looks great.

[hominoid]

That looks really nice, good job!

[joerg]

Last days I received all material I ordered assembled everything.
I drove some hundred kilometers already with the car and only thing thing I have to fix is the slow booting up of my LOS20. It takes over 1 minute to boot up and sometimes the cars bluetooth connection ends up with 'no connection'. Then I have to manual initiate the connection. As in my Volvo there is no audio aux input anymore I have to send the music by bluetooth to the cars media system. I am thinking of a an NFR52840 based bluetooth board that can sense the presence of my smartphone to give my C4 interface board a start impulse, so it can boot up earlier. I am waiting some seeduino XAIO board for this.
One other thing was the self developed usb-gnss driver of the LOS20, it reported the velocity in knots/s. I had change it to report it in meter/s. But after that the navigation was working very well.

The boards are installed at the downside of the speaker cover. I fixed some distance holder to it with 2k epoxy glue. First the from the back side of the Waveshare 8 inch lcd removed HDMI interface board, then the Odroid C4 with it's interface board I used last years already in the old car. Without some 90° HDMI connectors I was not able to put everything into it's place.
And @zyssai: yes it works with fpc extension cables of 20 cm. One of 40p for the lcd and one of 6p for the touch screen.

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[zyssai]

And @zyssai: yes it works with fpc extension cables of 20 cm. One of 40p for the lcd and one of 6p for the touch screen.

Thanks for this information, it can be useful
Really nice job, you did it!

If it can help, I am using iBeacon USB dongle powered by ignition.
This way, with Macrodroid app, my smartphone detects the iBeacon when I start the car, and launch wifi hotspot.



This is something like this:


https://a.aliexpress.com/_EvIzClz

Edit: I read again your post, not sure if it is suitable for you.
There is also some fpc HDMI connectors with different angles that can fit better for your usage.

[joerg]

The HDMI connectors I found are fine and suitable for my use case.
And yes, iBeacon usb dongle is nothing that can help here. The Odroid C4 is without power. An extern device is needed to send a start impulse to my interface board, so C4 can start up. This device need to be ultra low power to not drain the cars battery.

[rooted]

I think sensing your phone could be an issue, how will you keep this from happening when you're at home?

I would use the keyless entry, when you unlock the door it would initiate startup whenever you want with the bonus of no additional drain.

[joerg]

I thought already of this, but I placed this option to second place. To sense the keyless remote? I would need some information about frequency, codec, etc. Sure, if it is 2.4G I could sense if there is some traffic, but not decode if it is open or close. On other side, find the wire at the electrical system is also somehow difficult, means to open the interior cover of the door and search without having wiring diagram. Also I don't want to open the interior. At my former Volvo I have done this, but it was difficult.

[zyssai]

I would use the keyless entry, when you unlock the door it would initiate startup whenever you want with the bonus of no additional drain.

I thought already of this, but I placed this option to second place.

To help, can you explain why you do not prefer it this way?

[rooted]

Don't your interior lights come on when you unlock the doors remotely? There are many areas to patch into there.

[joerg]

Don't your interior lights come on when you unlock the doors remotely? There are many areas to patch into there.

Let me see tomorrow...

[joerg]

I made some progress with the XAIO NRF52840 modules I bought. One I programmed as iBeacon, the other as BLE scanner. I can scan if the iBeacon is some meters away and also I can scan if it is very near. So I plan to set the ignition input of my interface board when the iBeacon is in range. This way the C4 will start up. When the iBeacon is very near I will use another gpio output connected to reset. For that I will exchange the reset button with some terminal.
Both XAIO will have a Lipo battery. The XAIO board has charging circuit included. The iBeacon needs to be charged from time to time, while the other board is installed near the C4. This board will be powered by the Lipo during the car is switched off, and charged during the car is switched on.
But first me and my family will go on vacations, then I will finalize this sub project.

@rooted: there is not anything I have easily access to.

[rooted]

You have come up with a complicated but elegant solution, I look forward to hearing if it works out.

Enjoy your vacation

[joerg]

Thank you. But if it is complicated, I think it depends from the side of view. Open the interior of a modern car I find complicated. In my former Volvo I have done this once to replace the cable tree for the mirror. To find all well hided screws an fixing points. Risk of break something. There one part of the locking system became loose and I tried for more than one hour to put it back into it's position, big frustration. Things are always at impossible positions to reach. Meanwhile programming some controller brings joy.

[rooted]

My father owned an automotive shop for most of my life and I worked for him for a few years, I guess that's why it seems the easier solution.

[joerg]

Here is the Beacon made with XAIO NRF52840 (Seeed) with 3d printed case:

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To fix both half cases together I use 2x3 mm Neodym magnets, as can be seen in the 4 corners. On one half I pressed them as deep as possible. I had to drill the holes with 2 mm drill, after this they fit exactly, no need to glue them.

[zyssai]

Very good idea to use magnets, this way you can easy open it if needed.
Probably you could have heat them to insert in the holes?

[mctom]

Heating magnets above Curie temperature demagnetizes them, so not the best idea.
Unless that's well below 100 deg C, should keep magnets intact.

[joerg]

No I did not heat them. The holes were designed with 2 mm diameter and I printed the case with highest accuracy. But I couldn't put magnets in, so I drilled the holes with 2 mm drill. Then I could put the magnets with some force into the holes.

[zyssai]

Heating magnets above Curie temperature demagnetizes them, so not the best idea.
Unless that's well below 100 deg C, should keep magnets intact.

Every day I learn something, thanks

[rooted]

No I did not heat them. The holes were designed with 2 mm diameter and I printed the case with highest accuracy. But I couldn't put magnets in, so I drilled the holes with 2 mm drill. Then I could put the magnets with some force into the holes.

If you use Cura there is a setting called 'hole horizontal expansion', positive values increase the printed hole size.

[joerg]

BTW, I tried and tried to put the XIAO beacon into power off sleep mode, but first it didn't wanted to wake up with the button press. I found, that it only wakes up when I initiate the power off sleep mode from loop() function. But in the beacon example during setup loop is suspended for power optimization. So I tried to put it to sleep during a timer interrupt, It does not work. Now I found how to get it to work. I don't do suspend loop, but after setup everything I wait with delay and do a power off sleep at the end of setup(). So it seems that loop() is never entered.
The measured current when it is wake and sending BLE messages is 770uA, and during power off sleep mode 24uA. This way when I use the beacon several time a day, and it is waked up for 5 minutes and the rest of the day sleeping. The calculated average consumption is about 40uA. So 70% of the 150mAh Lipo are for about 3 month! Yeah!
When it is discharged below 3.6V, the internal LDO comes into limit to control the voltage to 3.3V. I programmed the internal LED to one pulse when the Lipo voltage is above 3.9V, to two pulses when it is between 3.9V and 3.6V, and three pulses when it is below 3.6V.

[mctom]

I'm not going to repeat my rant about batteries BUT!
150mAh capacity has been measured at certain conditions, probably full discharge from 4.2V or whatever, down to 3.0V or 2.5V, whatever the minimum voltage is.
It also was measured using some predetermined current, maybe 10mA.
If you plan to draw such little current, then the apparent capacity of a battery may actually increase beyond 3 months. On the other hand, it may as well be shorter due to self-discharge.
Just saying so you won't doubt your clever LED based warning system.

I would only suggest changing the LED indicator threshold from 3.9V to 3.7V for more meaningful feedback. See the picture below.

Your beacon may actually work at lower voltages than 3.3V, but there's no use investigating that because li-ion voltage drops rapidly near its depletion.

[joerg]

Thank you. I read about it and also your 'rant about batteries'. And I saw so much different curves. To get sure I will measure the voltage from time to time to get a curve for this Lipo I use. This was already in my head. Luckily I designed the case to be opened easily.

[mctom]

If your battery comes from a known source you may be able to find its datasheet and the proper curves.
Perhaps firmware could log time and voltage before each use? Don't know if there is any accessible memory in it.

[joerg]

The XIAO itself programmed as beacon looses after sleep the millis. After wake up it counts again from zero. So itself can't log with time. But I could log automated, because I send the millivolts with each uuid message. But I feel, it's to much for this small battery, to program an app for logging this values. It's ok for me to measure from time to time with meter...
And I will start today. I will charge it now full to 4.2V and it will become the first entry in the list.

[joerg]

A small update: It works very well. When I go to the car I press the button of the Beacon. It wakes up for 5 minutes and when I open the door of the car the Odroid C4 already starts to boot. This is enough early to let the cars' bluetooth system find the Odroid C4 and connects to it.

Here I update the measured voltages of the Beacon:
01.08.2023 - 9 p.m.: 4.200
02.08.2023 - 7 p.m.: 4.178
05.08.2023 - 7 p.m.: 4.136
12.08.2923 - 1 p.m.: 4.073
22.08.2023 - 5 p.m.: 4.035

To be continued...