Electronics > Projects, Designs, and Technical Stuff

Need help with _ _ _ schematic review _ _ _ for solar & supercap powered sensor

(1/2) > >>

doru.cazan:
Hi,
I am building a temperature sensor powered by a solar panel with a supercapacitor for backup. The main power part is heavily inspired by a Hackaday.io project: https://hackaday.io/project/175514-wireless-solar-powered-sensor-node/logs.
Will use a clock IC (below 1uA) to wake up the AVR MCU from deep sleep (also below 1uA); the MCU will set the clock IC timer alarm when initially powered then enters deep sleep. When the timer interrupt wakes up the MCU it will read the temperature then wake-up the radio part only for transmitting.
Are there any obvious errors in the attached schematic?
Many thanks!

zilp:

--- Quote from: doru.cazan on April 22, 2024, 06:32:53 pm ---Will use a clock IC (below 1uA) to wake up the AVR MCU from deep sleep (also below 1uA); the MCU will set the clock IC timer alarm when initially powered then enters deep sleep. When the timer interrupt wakes up the MCU it will read the temperature then wake-up the radio part only for transmitting.
Are there any obvious errors in the attached schematic?

--- End quote ---

I obviously don't know what exactly the application will look like, but a few things to consider:

- You are aware that the voltage supervisor eats probably half of your energy budget?

- You are aware that D2 leaks another quarter or so of your energy budget through R3/R4?

- Are you sure that the MTS01Z doesn't have any ESD protection diodes on the I²C pins?

doru.cazan:
Many thanks @zilp for the points below!


--- Quote ---- You are aware that the voltage supervisor eats probably half of your energy budget?

--- End quote ---
I was worried about this and the TLV809E data-sheet https://www.ti.com/lit/ds/symlink/tlv809e.pdf shows a typical 250 nA supply current.


--- Quote ---- You are aware that D2 leaks another quarter or so of your energy budget through R3/R4?

--- End quote ---
I am open to select a diode that is better from this perspective (does better means lower reverse leakage current?); do you have any suggestions?


--- Quote ---- Are you sure that the MTS01Z doesn't have any ESD protection diodes on the I²C pins?

--- End quote ---
Not sure. The data-sheet https://www.lcsc.com/datasheet/lcsc_datasheet_2210121700_Mysentech-MTS01Z_C5197400.pdf shows max 100nA input leakage current.

Can I assume that there are no ESD protection diodes?

Many thanks!

Peabody:
What does R2 do?

doru.cazan:
Hi @Peabody, not really sure, it is part of the Hackaday.io project design, link in 1st post. My best guess is that it helps limiting the supercapacitor charging current to even a lower value (30mA when the solar panel outputs 6V) compared to the shunt regulator capabilities, that can sink more than 60mA (according to the data-sheet max 100mA). Or, maybe to make sure the voltage drop on the D2 diode(depending on forward current) is low enough to allow the supercapacitor to charge to a higher voltage?

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod