Hi,
Apologies if this has been asked in the wrong category. On a project I'm currently working on, 2 times now I have had the problem of ~5V on the 3.3V pin. The first time I thought it was a soldering mistake, but now I'm sure something's fundamentally wrong, but I don't know what.
My project is creating an aluminium block with embedded thermistors, using a voltage divider to measure them. Recently I was calibrating my block, moving the block around, when I heard a loud POP! Suddenly, my ADC is just outputting 0 (even though I've checked the circuit and in fact, the ADC is receiving around 2.5V, what I would expect) so I expect the ADC is in some way broken.
That's when I realised that the same thing has happened again with my new Arduino, around 5V on the 3.3V pin. As I source power for my thermistors from the 3.3 V pin, my circuit is now using around 5V instead- this isn't a problem in itself, more confusing. The last time this happened I simply replaced the arduino, assuming it was a soldering mistake, and the project was revived. I've checked and no components seem burned out. I am really hoping and praying someone on here has seen a problem like this before, or could even suggest what the 'pop' was? I will replace my Arduino because it's very likely broken, I just don't want the same thing to happen again with my third arduino! I've had a long think and I cannot figure out what would be causing this, perhaps some feedback from mains [note the mains relay that I used to switch the live line of mains on and off]? Any and all comments or suggestions would be gratefully appreciated!
Hi,
I have not declared the analogue reference to external, could this be it? I have run it perfectly fine without doing this in the past. And this wouldn't explain why it only 'poped' and shorted once I moved the aluminium block? See attached documents.
Hi,
I understand that it is wrong to not declare it as External, however, I am just wondering if that is what broke it in this case given that it ran fine for hours before breaking.
Thank you for the tip about the kickback/flyback diode, I will add one of those in ASAP.
In regards to the pin, actually, my schematic is misrepresentative here- in fact, the relay is attached to the 5V line via a transistor with the collector and emitter connected to the 5V and the relay respectively, and the base connected to a digital pin.
Yes sorry that was missed from the schematic, it was a change made when I realised that I could not connect the relay directly to the pin. So if 3.3V is shorted to 5V; do you think that that could break my ADC? My principal issue here is that the ADC is just returning '0' regardless of the fact that there is a voltage on the analogue pin.
Ok, thank you for your help. I appreciate it. If you have any thoughts about why this issue suddenly presented itself rather than when the system first ran, do let me know!
If it happend twice when moving the aluminium block I would check all the wires running into the block make sure there is no small open copper part that can touch the block or feed back into another wire. Is the block earthed?
Hi, the block is earthed, but perhaps as there are wires going under it one of the wires happened to make electrical contact? Il heat shrink everything exposed and hope it doesn't happen again.
