Shad0wca7

So I could literally just do this and bring the IO to ground when I want to start the system up?

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Shad0wca7

Here is the latest version using a tiny84. It doesn't have a full USART so I'm not going to use it for that.

Power on/off will be controlled by the remote from the car head unit, it will only power the laptop on when remote & ignition are on. When it senses remote is off, it will turn the laptop off, this will be a neat integrated solution.

I also added an LED for status reporting and a voltage divider so it can measure the car battery and prevent a startup if there is a voltage problem.


Also, I was looking at that high-side driver and would love to use one.. If I could find out where to get them!? Maplin, Farnell & RS don't have them on their sites....

Curiosity

Looks good to me. Not sure about the TVS connected directly to the battery though. Probably isn't needed.

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XPort 1.24 -GPS port splitter, logger, and USB device resume fix

Shad0wca7

Mildly updated version, relay coil and transistor are now on a protected 12v supply


Soon to come: Buying the components and making it work!

scsirob

You may want to add a jumper block (say; on PA2-5) so you can select time settings for various situations withouthaving to reload software in the microcontroller.

I'd probably also connect the battery monitor to PA1, as you can then use the AIN0 function to cause a software interrupt when certain tresholds are exceeded, even when your standard routine is off doing something else.

I'd also add a diode between car_remote and +5V, as well as car_ignition and +5V, such that if the 12V_CONST connection fails you don't end up with 5V on your inputs and 0V on Vcc. Just a precaution.

I would add a zener to the battery monitor port. You now divide by 10, which means any surge of over 50V may damage the port itself. A zener should snub that. Better yet, do a search for high-speed surge protector diodes, they are much more effective than ordinary zeners.

Last but not least I'd think again about some of the components you selected. Why use a large 4004 (1A, 400V) diode when all you want is a signal diode? Why a 1A fuse when this circuit draws 100mA tops? Why a 7805 when a 4.7V zener would do just fine?

Shad0wca7

Thanks for the points, all definately something to think about. I'm not quite clear on your meaning of putting a diode between car_remote and +5.. I can't quite see how that works?

I will add a zener to the battery monitor port (4.7v) as well as replace the 7805 with the 4.7v zener as well. Definately a good idea. As for the 4004, I just have access to a lot of free ones of those at the moment and it won't do any harm to overspec that component. You are right that the fuse is a lot larger than it needs to be, worst case I'm sure 200mA would suffice.

Rob Withey

11

__________________
6yr old first install died 20/8/2005 as result of bad bios flash.

New system : 6x5x2" contains 1GHz C3 PCM9373, ISR based PSU, 512Mb flash DOM, 8Gb CF HDD, 98Lite, DirectShow based frontend.
GPS : Rikaline 6010.
Display : LTM08C351 + LVDS receiver.

Shad0wca7

I was pretty sure it was 10 too O_o. Another thing is that I was fiddling with the idea of using a transistor to signal the pc_on incase I can't pull the signal low enough with a diode. I don't understand how I can make the 2 pin header unpolarised if I am using an npn transistor?

Rob Withey

You can't (easily). Stick with the relay if this is a requirement.

__________________
6yr old first install died 20/8/2005 as result of bad bios flash.

New system : 6x5x2" contains 1GHz C3 PCM9373, ISR based PSU, 512Mb flash DOM, 8Gb CF HDD, 98Lite, DirectShow based frontend.
GPS : Rikaline 6010.
Display : LTM08C351 + LVDS receiver.

Shad0wca7

I just did a little test with the tiny84 and the diode method, works great so I will stick with that for now.

Shad0wca7

Ok, it is updated now.. hopefully this will be the 'final' version. I added another line for PC Power so now it doesn't matter how the switch is connected, both lines will be drawn to ground and the pc switch should toggle.

scsirob

The jumper block won't work this way. In your software you can define the AVR input pins as Hi-Z or with pull-ups. When you define them Hi-Z, they will be floating when no jumper is present, and you'll get random readings. When you define them with internal pull-up, your input will always read '1', regardless if you have a jumper or not.

You should get rid of the resistors and tie pins 2,4 and 6 to ground. Define the input pins with pull-up. No jumper always reads '1', jumper present reads '0'.

You probably also want to re-arrange the pins a bit. If you leave the jumper block on the MOSI/MISO lines, you will have to take all jumpers off before attempting in-circuit software updates.

Shad0wca7

It would work if I set the port to 0 however I suspect that setting with pullup and having the jumper to ground whilst keeping the resistors may allow ISP without removing jumpers.

scsirob

Not according to Atmel's spec. You can not set the port to 0, because it's an input, not an output. As input, the only options are Hi-Z or Pull-up.

If you jumper to ground and keep the 10k resistors in place you are building a voltage divider between the internal pullup resistor and the 10k resistor. The internal resistor can be anything between 30k and 60k (says the specsheet). If (worst case) your chip does 30K and you use a 10k pull-down, then your input sees ( 5V / (10k+30k) * 10K) = 1.25V. The AVR will see that as logical '1'.

The sheet defines logical '0' as < 0.3V, so you'd need at most 1.8K resistors to pull the input to a defined low level. That's probably too much load for ISP to work properly.

Take a good look at the spec sheet:
http://www.atmel.com/dyn/resources/p...ts/doc8006.pdf

Shad0wca7

Actually after reading the spec properly I'm pretty convinced the original setup will work, it will see a logic 1 otherwise it will be tri-stated and not used. The same applies for the remote_start and ignition pins etc as they all sense a logic 1.