Electronics > Beginners
Bit of a noob, needing project assistance.
starhawk:
I hope I'm in the right place -- there are at least three different subforums of this place that I could technically fit this thread into. If I'm in the wrong place, I would not object to being moved.
I have attempted to construct an Arduino project called a "Zorkduino". Info about the Zorkduino is here: https://github.com/rossumur/Zorkduino
My configuration is very similar to the recommended Zorkduino circuit, but I have made some deviations. A proper circuit diagram will be posted, below, shortly, along with at least one photo of the gloriously awful rat's nest I've grown inside this thing -- but for now, text will have to do. The deviations are...
(1) I am using a CH340-type Arduino Nano as the 'brains' of the circuit. Info about these specific Nanos, here.
(2) I am powering the entire contraption from a dual-rail 5v/12v supply, specifically a LaCie power brick. I have tried two different "sizes" of brick, as is detailed in the explanation (further below) of what's gone wrong.
(3) I have integrated a direct connection to a composite-input, 480x234-pixel-resolution, seven-inch LCD. This LCD requires 12v for power (unlike the rest of the project), hence the dual rail supply and messing about with Kycon connectors. (Note: in this case, "direct connection" does not mean that I skipped the two required resistors. They are present and accounted for.)
(4) The 5v rail is switched immediately after the Kycon connector and before any componentry other than the power brick. The 12v rail is not switched, as the LCD has a "soft" power button integrated that drives that function.
(5) The audio goes directly to a piezo can element (the little black can type, commonly seen in PC motherboards and the like) with no resistor or capacitor in between it and the Arduino.
(6) The entire assembly is mounted into a Solidtek ACK-595 keyboard, with the LCD on laptop hinges. It's not entirely pretty, but it's functional and I sort of like the kludge aesthetic (to the extent that such exists).
The problem, unfortunately, is that I don't seem to have any video out. When the 5v rail is switched off (just after entering the chassis), the video output is probably trying to render a "no signal" screen; however, the output is severely distorted. Switching on the 5v rail, 'straightens' the screen (rendering it normal and usable) but there still is no recognizable signal being picked up. (Photos will follow shortly.) Mind you, this is with a standard LaCie brick, 5v/2.0a 12v/2.2a. If I sic a LaCie "Bigger Disk" brick (5v/4.3a 12v/3.0a) on it, the brick just power-cycles.
The only thing I've been able to come up with is that maybe, because only the power side of the 5v rail is switched, and the 5v ground goes into the LCD as the signal ground, that maybe there's a short between power and signal grounds on the :CD controller and it's backfeeding something...? That seems a little shaky to me, but I don't know enough to entirely dispute it.
Photos and schematic, in my next post.
Any help or advice able to be given, is welcomed and requested. (I'm not here to whine.) An odd request: if you can't help, better to tell me than to just move on -- I have a bad habit of assuming I've been ignored, when the shadows get real long and I've not had so much as a peep out of anyone...
starhawk:
Schematic first. Not my best work, but most of it was done at 11pm last night, TBH, so I suppose it's good enough...
Now photos. I'm going to do this as a link to an Imgur album, because it's easier and just as good. Here's the linky...
https://imgur.com/a/R0DkBlM
Five images. The first is with the 5v power switched OFF. The second, with it ON. Third is an overall guts shot, fourth is guts-detail left side, fifth is guts-detail right side.
rstofer:
The Gnd side of the +12V and +5V supplies are connected together, right? I get nervous with the term 'dual rail', I'm hoping that the supply is simply a common dual output supply.
I also get nervous when you mention that a more powerful supply just cycles. That sounds really bad!
After you are certain the grounds are connected, check the voltage from +5 and +12 to gnd.
Will your monitor display 308x192? The author suggests viewing the video signal with a terminal - in other words, a serial input to the PC and something like Putty as a display. He says the display looks "Matrixy" so don't expect anything other than gibberish.
I don't know if the Tx pin he is using for video is also the Tx pin that goes out the USB port. If so, you might be able to use the IDE Serial Monitor even though the author is suggesting something else (or hasn't really thought about it).
I would disconnect the display and power up the Arduino. Does anything get hot? How much current does the Arduino draw (leave the switch open and bridge it with a DMM set to measure current).
Does that current change much when you plug in the monitor? It shouldn't!
I'm assuming you don't have a scope and troubleshooting without one is darn difficult. On my bench, I would simply probe the two sync signals and the video signal on a 4 channel scope. I wouldn't get a workable image but I would see if the Arduino was emitting anything.
Put a blinking LED project back into the Arduino to see if it has been smoked. This power brick cycling just can't be good.
Are you actually running the video down the shield of a coax? I would expect the shield to be grounded on both ends and, more importantly, on the display end. What kind of display are you using? The design uses NTSC, a common TV set with composite video input (yellow jack). It won't work on any kind of digital monitor. I have one of those 7" monitors and it accepts composite video so I suspect you have the right thing as well.
I guess I don't really understand what I see on the schematic around the coax...
starhawk:
Separate 5v/12v grounds, per the insistance of the power supply in question. This is given in the schematic.
The supply is known good.
The monitor is composite video; the output from the Arduino is not serial TTY but rather matching composite video. It is text-only video (if that makes sense) but it is most certainly not TTL serial or RS-232. As for resolutions, the monitor is capable, last I checked, of scaling...
I believe the TX pin goes to the CH340 as well as to the video signal -- confirmation of that would be in the second link in my first post, to the info about the CH340 Nano boards.
The video signal is travelling through coax part of the way -- it's two side-by-side wires (signal and ground) to where it joins with the black cable from the LCD, and then it is coax from there into the LCD. The cable with the coax video and 12v power/ground leads has an additional shield which I believe is grounded on the LCD side -- it is unconnected anywhere else. This information is reflected clearly in the photos at the posted link in the second post.
I have an o-scope (a very old Tektronix 422) but it's quite sizable, quite heavy, and I quite don't know how to use it :-[
rstofer:
--- Quote from: starhawk on November 18, 2018, 05:56:38 pm ---Separate 5v/12v grounds, per the insistance of the power supply in question. This is given in the schematic.
--- End quote ---
Since you are carrying a ground with your video signal, the power supply grounds will be connected through the coax.
If it is not permitted by the power supply for these grounds to be connected, you have the wrong supply! Why is one of your supplies cycling? Again, that Arduino current measurement, with and without the monitor connected, may give some indications.
There are no one wire circuits. You can't output a signal without a return path and you can't use a signal inside the display without connecting to that return path. What they do with the power input is unknown (to me) but I suspect one side is grounded to the electronics ground. Probably the (-) side.
I would bet that if you measure voltage between the two grounds, it will be zero. You can compare this to a similar measurement of the power supply by itself where the value is probably floating around.
The author mentions viewing the video with a serial monitor. Since he is using the Tx pin, I assume it also comes out the USB port and, if so, maybe you can pick it up if your serial monitor program will go fast enough. At least to the extent of knowing whether there IS a signal.
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