First of all thanks for the project, it’s really amazing. I bought an original IoTaWatt unit months ago and it’s amazing.
I am building my own pcb based on the original schematics and my supplier (JLCPCB) does not have the PCF8523T, besides it is very expensive ($4-5).
I found the DS1307Z which has similar features:
- Battery backup
- Counts Seconds, Minutes, Hours, Date of the Month, Month, Day of theWeek, and Year with Leap-Year Compensation Valid Up to 2100
I’m not worried about changes in the source code, I’m a programmer and I don’t think it will be difficult to adapt the readings to the new RTC.
It seems that the DS1307 is vulnerable to temperature changes and can cause deviations of one or two minutes a day. Would this be a problem? I think the time is updated with an external server, is that correct?
In JLCPCB they also have the DS3231 model that incorporates correction against time lags giving a precision of 172ms/day (in the worst case) but it is really expensive ($7-8), although the crystal is already integrated.
To summarize, is the accuracy of the RTC really important?
As long as you have access to a time server, the RTC is checked and corrected every hour.
But don’t run off and go through all of that. You can substitute M41T81M6F but that has gotten hard to find as well. I recycle parts from old boards that I use for R&D. If you PM your address, I’ll send you a used one (or maybe even a new one).
They also have no stock of M41T81M6F at JLCPCB. I can get cheaper on Aliexpress, so I think I’ll go for that option.
I’m from Spain so shipping is probably much more expensive than ordering it directly from China. They sell 10 uds for €7.21 shipping included.
Just to add, I’m doing the layout in EasyEDA with JLCPCB compatible parts. This allows you to order PCBs with SMT assembly directly. It is for this reason that I am migrating the original design.
Although PCBs do not have certification of any kind, it can be interesting to do tests and research.
I also have the idea of making a development with the cheapest components I can find, simply to satisfy my curiosity.
FYI you can just eliminate the 4 TVS diode ICs. I never put them on prototype boards. The MCP3208 has I think protection to 5KV. The diodes were just to pass the RED review for CE. It probably would have passed the actual test without them.
In the datasheet, MCP3208 has:
ESD protection on all pins…> 4 kV
i will delete them.
Thanks for this information, I am not EE and my knowledge is limited, even so I am learning a lot with this project.
Is there a thread that summarizes the information about each of the components? I have seen that there is a lot of scattered information but I have not found an all-in-one thread, maybe I can create it when my prototype works as a reference.
They all have data sheets.