Multi Interface by Eugenius with BME680 and SenseAir S8

[fluppie]

https://github.com/fluppie/Temperatu...sor_BME680_1.0

Here you can find my code to use a BME680 with the Multi Interface by Eugenius

I also want to add a CO2 sensor, the SenseAir S8. This sensor is a bit power hungry, 300mA peak and 30mA continous.
To measure how long the peak power occurs, I bought a chinese Digital Scope. The peak is around 100ms and 200mA. I used a 1 ohm resistor in series to the S8 5V line to measure the voltage. The scope says the average is 18 mA and Irms is 40 mA . So I guess that should be do-able for the Multi Interface?

[Eugenius]

Try&Error.... 200mA is alot :/
MI uses MicroBCU. MicroBCU can 100mA
You need big buffer capacitors...

[fluppie]

https://electronics.stackexchange.co...supply-circuit
Guy writes:
So if we want a voltage drop of say 100mV or less and we have a current spike of 5A for 1ms then...
C = 5A * 1ms / 100mV = 50mF.

In my case I have C = 0.2A * 100ms / 100 mV = 0.2 mF = 200 µF
I have some 330µF caps laying around. Should work then?

[Eugenius]

Try&Error
I would place a current limiting resistor between MicroBCU an Cs to limit current spikes to 100mA

[fluppie]

I think I will solve it differently. I have a 5V and 12V Meanwell DIN Power supply in the distribution board. I'll use white and yellow for a secondary 5V supply.

[Ing-Dom]

thats a possible solution, but not as easy as it looks like in the first place.

Think about voltage drop on the line, which is significant at these low voltage level. It is preferable to use e.g. 24V and use a step-down in the device.

Second problem is, that altough KNX will most likley work, it is not specified that you connect KNX GND to another GND, what you have to do when you source from 2 points.
You should use galvanic isolation in that case, I would prefer a ADUM1201 between µBCU and µC/Sensor.

[fluppie]

That's a good idea/tip. The senseair S8 has a serial port, so I could use the ADUM1201 between the Senseair S8 and Multi Interface. The BME680 can be powered directly from the bus. I'll order some ADUM1201's.

[Eugenius]

ADUM1201 is for UART
ADUM1250 is for i2c...

[Ing-Dom]

why do you bring up i2c and the 1250? the senseair has a uart interface..

[fluppie]

I think just in case I want to power the BME680 also from the secondary power. But since the BME680 is low power I'll power it from the Multi Interface.
Senseair has a new low power sensor, the Sunrise https://senseair.com/products/power-...seair-sunrise/ but I don't know if this one is more expensive. S8 is around 59-60 euro's from a company in Sweden (https://firstbyte.shop/)

[tuxedo]

fluppie

This sensor is a bit power hungry, 300mA peak and 30mA continous.

How long does this peak take?

I have ~200mA for my latching relays and need ~6000µF to buffer from µBCU. Relays take ~50ms to set/reset.

So, 300mA would be quite a lot. External supply makes most sense I would say.

I have another project running a kind of air quality sensor, eating also several hundret mAmps. There's also only this option: Use a separate supply.
But in my case, I need no extra isolation, as the sensor uses a "heating resistor" and a measurement resistor. Fortunately the heating resistor can be powered independently.

[fluppie]

The peak of 200mA is for 100ms. So quite short.
But I "resolved" the problem by ordering a Senseair Sunrise (https://senseair.com/products/power-...seair-sunrise/) sensor, which uses LED = low power.
Peak is reduced to 125 mA, average over 16s is less than 1ma .