Hello,
how many Atlas Sensor (isolated/no-isolated) carrier boards can a Raspberry Pi handle over I2C ?
On 3V3 the Pi got maybe 500mA.
One Carrier Board 40-50mA → so the Pi can handle maybe 10 Carrier Boards.
I am right ?
How can i get more ?
Thanks
bg
mfg
Unknown, without a product to inspect the datasheet of.
First of all, do you really even need Atlas sensors and carrier boards? Those are considered pretty high-end hardware and are usually used for laboratory-level scientific data gathering. There are a wide range of sensors out there that are much less expensive, and work just as well for running a simple home mushroom or hydroponics system.
Well that all depends on which I/O bus on the Pi you are actually using… Are you using the USB carrier boards and connecting the I2C sensors to the USB ports on the Pi? Or are you using I2C carrier boards and connecting directly to the I2C pins on the Pi’s GPIO header? There’s a big difference.
Either way you never want to max-out a current rating on any kind of circuit or device. Running constantly at the max current rating will drastically shorten the life of the circuit or device and it will burn out pretty quickly. A good rule of thumb is to never constantly run a circuit at more than 75-80% of it’s max current rating.
Those carrier boards are rated at 50mA draw, but what about the sensors you plan on attaching to them? The sensors themselves will also add some current draw as well, so you have to factor for that.
It’s usually best practice to avoid powering more than 2 or 3 small peripheral devices directly from the Pi’s GPIO header. It’s usually better to power peripheral devices from their own dedicated PSU.
Each device connected to an I2C bus is required to have it’s own unique Hex Address. This address is often hard-coded in the device and can not be changed, which means that you can only use 1 of that particular device on any given I2C bus. There are some devices that allow you to select between 2 or maybe 3 addresses on the device using a jumper or trace-cut, in which case you’d only be able to use 2 or 3 of that device on any given I2C bus. I’m not sure how the addressing works on the Atlas I2C sensors, but I would imagine that it’s the sensor boards, and not the carrier boards, that have the addressing.
To add more I2C devices, or to use more than 1 of the same I2C device on a Pi, you can use an I2C expander board to add another I2C bus, but the Raspberry Pi 4 already has 6 available I2C master busses. And the Pi 3 has 2 available I2C busses.