What happens to Particle Core's analog input if?

Hi there,

I have a AC Current Sensor like this SCT013-030 (30A/1V) for energy monitoring.
And this is connected to my Particle Core like this:

Do you know it is safe for the Core if the (5V) power supply is down? (no more voltage (3,3v) in the divider circuit from the core, but potential current in the sensor)
From my point of view, the analogue input (A3) of the Core will be exposed to negative voltage… right? (because we loose the mid point)
Do you see any solution or is it safe for the Core to keep it like this?

Hi @JP2M

Your circuit is not right for that kind of current transformer. Did you read the linked report off of the page you pointed to?


Current transformers need what is called a “burden resistor” to convert the current output of the transformer to a voltage you can measure.

1 Like

No it seems that this sensor have a voltage output (30A/1V) perhaps the burden resistor is already inside…?

But this is not responding my initial question

Hi @JP2M

Based on the datasheet, I think you are wrong about that sensor, but let’s go with it for now.

You seem to be asking if leaving the AC sensor connected when the Particle device is not powered is safe or not, right? The datasheet for the sensor shows a TVS (transient voltage suppressor) but this is not likely to help at 0-3.3V. The Core and Photon both have protection diodes on the inputs but it would be less than ideal to completely depend on them in the long term–for testing it will be OK. The simplest thing would be to add back-to-back 3.3 zener diodes across the input and ground for added protection.

Good idea! I will check that in detail, but zener should normaly work in case of issue with power.

my sensor is a voltage output (please check datasheet below, with Current output or voltage output)

Hi @JP2M

That’s great and it looks like you are right, but that is not the datasheet you originally linked to!

1 Like

Thank you, I’ve now change the datasheet