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Running a camera without a screen?

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Re: Running a camera without a screen?
« Reply #10 on: 22 / April / 2015, 06:10:48 »
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The romlog is a canon firmware feature, so it means the canon firmware did not generate a romlog for whatever error caused the shutdown.
Hm. Guess I will try going the UART route. Maybe there will be some hints there. I believe I have identified the UART pins.

I wouldn't expect a dedicated "detect" pin, more likely some specific conditions are expected. Presumably, it can be spoofed with enough effort.
Unfortunately I have not found much detailed tech info for the A4000. Does not appear to be a service manual online. The only chip on the device that I cannot identify is the AA1900, which is listed as a "video processor" on that russian site, but I don't think it has enough pins to be the LCD driver anyways and there is no datasheet I can find. Can't locate a datasheet for the LCD either, although it does have 40 or 41pins which is a typical number for a TFT LCD (accounting for 24x color signals, h/vsync, clock, power/gnd, backlight power). AFAIK these LCDs don't typically have any "read" interface capability, but it does have logic onboard so it is possible. I assume there is a backlight drive circuit on here which is driving a constant current, it may be an error related to the current level which would not be hard to spoof (if I can figure out the correct pins). As is typical though... everything is incredibly tiny and impossible to probe on this board! There are some LCD breakout boards available on the net, possible I could find one that matches.

I am willing to take this a little deeper on the science fair level, but at some point it will become not worth it! Appreciate all the tips on here!


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Offline reyalp

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Re: Running a camera without a screen?
« Reply #11 on: 22 / April / 2015, 16:09:20 »
Guess I will try going the UART route. Maybe there will be some hints there. I believe I have identified the UART pins.
I would be somewhat surprised if anything useful is output on the UART, but it's worth a try. Verbose messages tend to go to the "camera log" which is just that isn't saved / displayed unless specifically requested. Fatal errors usually trigger some kind of romlog.

If you do successfully connect the UART, adding the relevant information to http://chdk.wikia.com/wiki/UART would be appreciated.

One other thing that would be interesting to know is if the shutdown occurs before or after CHDK starts. When CHDK boots, the camera actually starts the normal firmware, then somewhere in the startup process it notices the card is locked and diskboot is present and reboots into CHDK.

If you can make your own CHDK builds, you could put an LED blink early in the CHDK boot process (described in http://chdk.wikia.com/wiki/Debugging#Using_LEDs_directly) to find out. If the shutdown happens after CHDK is loaded, it may be possible to bypass in software. If it happens before, then there is no chance of a software solution.
Don't forget what the H stands for.

Re: Running a camera without a screen?
« Reply #12 on: 22 / April / 2015, 18:27:22 »
I got it. No UART needed. I traced the LCD backlight signals back to two convenient pads near the LCD connector. Put a 330 ohm resistor between these to simulate the backlight load and I am in business! My limit was two simple hardware mods to the board, which I met. Added one 330 ohm resistor on the power on signal so it powers on when power is applied and then one for the backlight.

Appreciate all the tips! I still have to figure out how to configure all my settings (since the camera settings reset after each poweron without the backup battery which is inexplicably on the button flex harness), but this should be doable with a CHDK script or PTP.


 

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