Timeline for Why is there a short between my VCC and GND in this circuit?
Current License: CC BY-SA 3.0
17 events
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| Feb 3, 2018 at 21:48 | comment | added | Dan Mills | Agreed that the lack of decoupling is a problem, but even once you have solved that there is an unrelated issue, FPGAs of the reasonably recent sort will not appreciate having pins pulled up to 4.8V, R3,4,5 should be pulling up to whatever the IO bank voltage is (Likely 3.3v), no more. You may have damaged the FPGA at this point. | |
| Apr 13, 2017 at 12:32 | history | edited | CommunityBot |
replaced http://electronics.stackexchange.com/ with https://electronics.stackexchange.com/
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| Dec 25, 2016 at 14:44 | comment | added | SamGibson♦ | [cont'd] Note that the recommendation for (at least) 10uF capacitor near to the sensor, is in its datasheet (I just found it near the bottom of page 6). Therefore you should expect to add that to each sensor, irrespective of any other results of your troubleshooting. I would start with comparing the outputs of your 2 existing sensors using just a scope (no attached comparators, in case any faults are dragging down the sensor output voltages), with power from the previous "good" 5V supply & short power cables. Any difference between the two sensor's outputs may suggest damage. | |
| Dec 25, 2016 at 14:44 | comment | added | SamGibson♦ | @Eran - Hi - Those bursts of spikes (notice the pattern in the spikes - 8 spikes then a similar length gap) looks like the sensor is trying to work. However I agree the output looks abnormal. I think this specific question is too "tainted" by the original multimeter testing question, to now be changed into what the question should be. I suggest to remove the scope photos from this question; start a new question (mention this one), give brief history, then add scope photos (power & output) from both sensors. Any difference in sensor behaviour may suggest (at least) one is now faulty. | |
| Dec 25, 2016 at 14:11 | comment | added | nettek | I added some screenshots from a scope. The comparator seems to be working but the sensors are not :( This is when testing with the DC power supply like I did once. Do you think capacitors will help here? Because if those sensors worked for me once I think it's possible that they are ruined and caps won't help in this case. | |
| Dec 24, 2016 at 19:50 | history | edited | SamGibson♦ | CC BY-SA 3.0 |
Significant rewrite to include the X and Y terminology in the answer, to better explain why I refer to it as an XY problem.
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| Dec 24, 2016 at 19:43 | vote | accept | nettek | ||
| Dec 24, 2016 at 17:33 | history | edited | SamGibson♦ | CC BY-SA 3.0 |
Added links to other EE SE questions related to Sharp IR sensor power supply decoupling and/or output signal filtering. Added hypothesis why external power supply worked.
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| Dec 24, 2016 at 17:24 | history | edited | SamGibson♦ | CC BY-SA 3.0 |
Added links to other EE SE questions related to Sharp IR sensor power supply decoupling and/or output signal filtering.
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| Dec 24, 2016 at 16:30 | history | edited | SamGibson♦ | CC BY-SA 3.0 |
Added links to other wepages about the Sharp distance sensors and additional decoupling capacitors
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| Dec 24, 2016 at 16:26 | comment | added | SamGibson♦ | @Eran - Great. As you said, I would also start with going back to the "working" config and retesting. If that works, move forwards from there. Comparing the sensor power waveform on the 'scope, between the working (external power supply) and failing (DE0-Nano power supply), will help confirm or deny my hypothesis. However even if my (lack of sensor power decoupling) hypothesis is wrong, I wanted to help by stopping you wasting your time on those continuity testing results. Then you can move forwards with investigating whatever your problem really is :-) Also, see new links in my answer. | |
| Dec 24, 2016 at 16:15 | comment | added | nettek | Yes I saw your edit, thanks for the additional info. I am already planning to retest this tomorrow with the previous configuration. I'll also do what you suggested with the scope and provide screenshots, and if really needed, add the capacitors. I just really hope I didn't fry the sensors or the comparators. | |
| Dec 24, 2016 at 16:06 | comment | added | SamGibson♦ | @Eran - Understood & thanks for the schematic. It has confirmed there are no decoupling capacitors, so it has already been useful. While you updated the question, I was also updating my answer, and added an additional paragraph. IMHO you have several choices: (a) you could guess my hypothesis is correct, add (eg 47uF) cap at each sensor (not 15cm away) and retry; or (b) use an 'scope to view the waveform on the sensor power pins, in the "failing" configuration (powered by the DE0-Nano) and supply those 'scope screenshots; or (c) go back to the working config and retest, as in my answer. | |
| Dec 24, 2016 at 16:00 | comment | added | nettek | About the capacitors - should they be between VCC and GND? Can they be soldered into the board I designed (about 15-16 cm from the sensors?) | |
| Dec 24, 2016 at 15:58 | history | edited | SamGibson♦ | CC BY-SA 3.0 |
Added additional paragraph
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| Dec 24, 2016 at 15:56 | comment | added | nettek | You're right about not providing enough information - writing this question and drawing the schematic took a long time! :) I have edited the question, stating that the output of the sensor give me 0V, whether there is an object near them or not. Also, is there any other information I can provide? | |
| Dec 24, 2016 at 15:46 | history | answered | SamGibson♦ | CC BY-SA 3.0 |