We’re used to interfaces such as I2C and one-wire as easy ways to hook up sensors and other peripherals to microcontrollers. While they’re fine within the confines of a small project, they do have a few limitations. [Vinnie] ran straight into those limitations while using a Raspberry Pi with agricultural sensors. The interfaces needed to work over long cable runs, and to be protected from ESD due to lightning strikes. The solution? A custom Pi interface board packing differential drivers and protection circuits aplenty.
The I2C connection is isolated using an ISO1541 bus isolator from TI, feeding a PCA9615DP differential I2C bus driver from NXP. 1-wire is handled by a Dallas DS2482S 1-wire bus master and an ESD protection diode network. Even the 5-volt power supply is delivered through an isolated module.
Whether or not you need this Raspberry Pi board, this is still an interesting project for anyone working with these interfaces. If you’re interested, we’ve looked at differential I2C in the past.
“I also added the DS9503P ESD Protection Diode, which gave my circuit approximately 27 kV of isolation.”
Nope. Not with that series R. and not with that PCB layout. Methinks his ‘Zeus filter’ may have similar problems.
Thinking about it more.. my actual application (this was a test board) does bring the OW right up to the connector and I will remove the resistor and tighting the grounding.. do I need to do more?
Your clearances and creepage distances could be improved.
there is no isolation in form factor of Pi against 27kV :D *it will simply jump over what ever”
It’s always nice to have a sign and real cutoff hardware for these situations, saw some crazy automation events due to HV related faults.
give me more detail? I am eager to make it better. I am following the datasheet and reference design at https://www.analog.com/en/products/ds9503.html. what did I miss?
27kV could jump up to 30mm in air (worst case) so you could pot everything is special isolating epoxy, and put all components as far away from each other as possible. also induction might still be a problem and could maybe fry some stuff.
Remember that I2C is a board level bus, not an industrial/network bus.
I think HDMI, DisplayPort, DVI and VGA missed this memo
If you’re not optically isolated, you’re not ESD protected in any meaningful way.
Given the voltage present in a lightning strike, I wouldn’t even try to design my own system with copper. Instead I’d power each node with battery and/or solar, and communicate via RF. Then a strike takes out at most one node.
Is that the Aardvark from the Pink Panther Cartoon?
I’m pretty sure it is 🤣
Just running I2C over several meters is problematic, increased capacitance will dull the edges on bus transitions, smaller pull-ups will somehow mitigate that but will consume more current, going RF with something like nRF24L01 mesh sounds overall a better strategy, also limiting the exposure to lightning strikes.
If you’re worried about 27kV getting into your data lines, the solution is to run them over fiber.
Nice, where can i buy one and for what they are used for?