Hi, I have an Particle Argon board reading a bunch of data from a range of sensors, some of which have 12V and 5V supplies. These sensors can be considered field devices, and connected to the main datalogging box via ethernet cabling. Occasionally due to incorrect wiring on the remote end, this can result in inadvertently exposing 12/5V to either the 5V VUSB or 3.3V power rails or the GPIOs (which I understand are rated only up to 3.3VDC max). I believe it has been this overvoltage from the 12V that has killed my Argon in the past.
Can anyone offer any practical solutions to protecting my Argon board from overvoltage?
Do I need to install zener diodes on each of the GPIOs and the 5V and 3.3V supply rails, that will cater for either 5V or 12V exposure?
Furthermore, if either the 5V or 3.3V supply rails on the Argon are supplying sensors in the field, and there is a short circuit (e.g. from a damaged sensor submerged in water), what is an economical way to quickly disconnect the affected circuit, without shutting down the rest of the datalogging from the Argon?
I would really appreciate some guidance, thanks in advance!
These are good questions to ask as the longevity of your device in an outdoor environment will depend on how well you protect it.
First, I build and deploy sensors for outdoor use. I don’t have to worry about 12V sensors like you but I have developed a carrier board that is open source. I employ a few different technologies on this board and you can see if any of them might be helpful for you. I could not have done it without the Particle community who gave me many of the solutions incorporated into the design. This board has protected my Borons very well in parks and recreation facilitates in the US and Canada.
There are a few different issues you have to think about with protection:
ESD or transients
Based on this project and some others I have worked on, here are some ideas:
A simple and very robust way of protecting your. device is to use opto isolators. They can (before the current supply chain issues) be cheap and are easy to implement.
Zener diodes are a good way to cap the voltage ( I use one on the carrier board as the Argon cannot take 12V while the Boron can) just make sure they can handle the power you need to dissipate if needed.
Short circuits can cause high current drain. I use fuses as they are cheap and very versatile. Unfortunately, if they are blown, you need to replace them. For this reason, you might look at a PTC which will reset itself (not back to its former self but close) once the short is cleared.
Coupling a varistor with a fuse can protect against both over current and over voltage.
For higher speed GPIO lines - like i2c lines - you can take a look at the TVS diodes.
There is a lot here, and this community has a number of experts. Hopefully this list can get you started.
Thanks @chipmc and @no1089 , I appreciate the suggestions as a starting point.
Do you have any examples or part numbers for opto isolators?
I’ve tried using PTC fuses, to protect against short circuits, but they are too slow to act, and instead of isolating only the affected circuit, my solar charge controller shuts down, and takes down everything. I have looked at things such as high side switches or efuses, but they seem to be more expensive, complex and harder to get parts for.
Attached, is an example of one of my RJ45 connection from my sensor to the Argon.
The 5V supply is the same supply to the Argon VUSB supply rail, via a boost converter/solar regulator, and the 12V supply is via same solar regulator, but a different boost converter.
I am assuming that if wires are crossed, and the 12V touches the VUSB (5V rail), any of the GPIO pins, or the ground of the Argon, that it would fry it? So at minimum, I would need to put zener diodes/optos on each of those?
With the current chip shortage, getting a part number that you can buy is a challenge but this one is in stock at Digikey and is a close match to a part I have used in the past. One note which may be obvious, these parts protect GPIO lines not power lines.
On the PTC fuse, one of the attributes is the time to trip. Here is one that can trip in 8mS which may be worth a look (provided other specs work out - I selected this purely on time to trip):
A few suggestions on the wiring you show:
Perhaps it would make sense to put 5V on pin 1 and 12V on pin 7
If you are using pre-crimped wires and board mounted sockets - how big a risk is there of a short? Your application will answer this. I don’t for example put reverse polarity protection on my power connectors as I control the socket, the connector wire and the battery.
Yes, applying 12V to the VUSB pin on an Argon will dry it. you may want to look at a part like this to protect it: