| Electronics > Beginners |
| Bit of a noob, needing project assistance. |
| << < (3/9) > >> |
| starhawk:
I can see a crystal on-board the Nano. It's super tiny... roughly an 0201 part. The Arduino is running off the 5v rail of the external power supply. One of the clever (ish) things about these CH340 "Nano"s, is that you don't have to use the internal regulator. The 5v output pin from the regulator to the outside world, is also an input pin for a regulated 5v external supply. |
| rstofer:
--- Quote from: starhawk on November 18, 2018, 07:02:02 pm ---I can replace the partial-coax lead with all-coax, that's not a big deal. As for the current measurement thing -- I think you may be slightly confused. It's the more powerful supply that's cycling -- if I were drawing too much current, the lesser of the supplies would be objecting, not the greater. Probably I've got something very slightly shorted somewhere and it's picking up leakage current. My soldering skills are not the best. I will, however, check the power supply grounds to see if they are internally connected. --- End quote --- I think measuring the voltages will be helpful. The way I see it: The smaller supply has current foldback and when the circuit seems to draw too much current, the voltage folds back until the current is reduced. OTOH, the larger supply can put more current into the problem and it begins to look like a short circuit. The voltage doesn't fold back, it cycles. I have absolutely no basis for thinking that way except that I am bothered by a larger supply cycling on a load that a smaller supply doesn't object to. But maybe it is objecting! Maybe we don't have the voltages! The reason for measuring the Arduino current is to verify that it is a few mA (I don't have mine handy so I don't have the number) and not AMPS. Taking two measurements (with and without the monitor) may show that the interconnection to the monitor is causing a problem for the Arduino. It shouldn't because of the resistors in the video signal and, again, I have no reason for thinking this way but it's the way I would proceed. When I do these kinds of projects, I want to know voltages and I want to know currents. In fact, maybe that's why, after decades of using wall warts, I bought the Rigol DP832 - it has digital readouts of current and voltage for each channel and I can set the constant current and overcurrent levels to prevent breathing magic smoke. I found this quite handy when I was bringing up a Z80 project that had a bus conflict. Without current limits, I would have been buying more chips. |
| starhawk:
Fair enough. Let me make and eat dinner and I'll stick a multimeter on the dang thing afterwards... I should check for shorts on the power wires anyhow. Not all of the soldering in that thing is my best work! Also, if you (or anyone else) can give me "explain like I'm two and my name is Ralph Wiggum" level instructions (i.e. 'turn this knob to this setting'), I'll drag out the ol' 422 (the o-scope) and post pictures of what it says. I'm not unwilling to haul it out -- I just don't know how to work it properly. Yet. I've got the manual, I've got the time, I just haven't taken the bother to do it, even though I should and I don't have good excuses or reasons... |
| starhawk:
I think I figured it out, and boy is this embarrassing. It's also a testament to the ruggedness of the various chips involved... I wired the supply rails backwards :-[ I've got 5v going to the LCD and 12v going to the everything else. Ooooops! I don't think I've cooked anything, but, by the same token... ya know, guys, I really don't think it's going to work out very well, wired like that... I know exactly how it happened, too... to get the power socket to fit, I had to stick it in upside down. Time to get out the iron :-\ |
| rstofer:
If the scope powers up with a trace on the screen, everything in the upper left row is fine - I'll ignore it. The upper right is time per division on the graticule. Set it for 5 ms for now. The lower left is the volts per division on the graticule. Set it for, say 1V. Touch your finger to the tip of the probe and you should get some kind of (probably) distorted sine wave. The rest is just details. For using both channels stacked on the display (with 10 division) set each to 2V/division and with no inputs, separate them with channel 2 near the bottom half (1 division off the bottom) and channel 1 at the center line using the channel Position knobs. Now, 5V signals will move each trace up about 2.5 divisions. For both channels, you will probably want to select DC coupling with the switches near the input connectors. There is a channel selector knob right between the 2 Volts/Div knobs. For dual channel use you need to select either Chopped or Alt(ernate). Chopped displays both traces at the same time by selecting one and then the other at some high frequency. Alternate displays one complete trace and then the other complete trace, alternating between them. Triggering locks the signals to the scope. You will probably want to trigger on Channel 1, perhaps rising edge and DC coupled. You adjust the Level knob up or down until the trace locks in place. Write a simple Arduino program (or modify a Blinky program) that just toggles an output pin as fast as the CPU can run, no delay() calls. Scope that pin and play with the knobs and dials until it makes sense. Use a PWM example and see how the pulse width changes. The Arduino is an excellent source of signals to test! I'm looking at page 14 here: http://w140.com/tek_422.pdf Watch any w2aew videos on scopes, they are excellent. His project for displaying NTSC on a scope if really great! Just the thing for your project! Zork on a scope! Hit up his home page on YouTube and see what you find. I know he did a lengthy presentation to a local HAM club There is a sticky at the top of this forum, 'Oscilloscope training class (long)'. |
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