Hi.
Does your RTC have a battery attached? If not, it cannot maintain the time after being disconnected from the power source.
Regards,
Sara

Hi Sara,
Yes, all three have their batteries and they are above 3V.
Regards,
Renaud
 

Hi Renaud,

What are the battery, measured voltages; disconnected from USB?  Measure with battery installed in the RTC (under load).  Battery may show a good voltage out of the RTC; however, not be able to power the RTC.

If you do not have a voltmeter, try a new, fresh battery.

William

Hi William,
Thanks but the batteries are indeed above 3V on the RTC when disconnected from USB.
I had a good look at the Maxim specs about the DS1307. Like you I was thinking about a PS trouble. Contrary to what is said nearly everywhere it should NOT be powerered at 3.3V. The specs are 4.5V to 5.5V. Obviously many are operational at 3.3V but some could not be either. Well, I thought that was the culprit as mine was supplied at 3.3. So I happliy plugged it on VSYS but with the same result. Also the BAT min spec is 2V.
Here I am! Any new ideas received gratefully!
Best regards,
Renaud

Does your DS1307 have pull up resistors on I2C, SDA and IC2, SCL to Vcc?  Not all Breakout boards have these resistors; values can range from 4.7K to 10K ohms.

Also, check soldering of header pins; for a cold solder joint.  Re-apply soldering iron to heat joint; until solder flows at joint.  

William

Hi William,
Yes, the pull up resistors were to be my next move. The Maxim specs call for them. 
Yesterday I tried to use the Pico inboard pull ups:

I changed:
i2c_rtc = SoftI2C(scl=Pin(5), sda=Pin(4))

to:
i2c_rtc = SoftI2C(scl=Pin(5,Pin.IN, Pin.PULL_UP, sda=Pin(4) Pin.IN, Pin.PULL_UP))
but got an “invalid syntax” with that. So this morning I added real pull ups on sda/scl but again to no avail.
About a bad solder or connection I have the same result with three builts. Two on breadboards, the third soldered. BTW I have a (too!) long practice at soldering William but that doesn’t exclude bad ones as you say.
Now the same on three different Picos with three different RTC!
Thanks
Renaud

Good Morning Renaud,
 
The “invalid syntax” pertains to an error in the code; not hardware.  I am not knowledgeable in the Raspberry Pi Pico or MicroPython; I have coded for a long time in C++.

I did check out a blog post on the Pico and MicroPython; shows how to init the I2C sensor and how to define the pins.  Hope you find it helpful:   Raspberry Pi Pico and I2C
 
Regards,
William

Hi.
Let’s just recap what you need to do. I don’t think your problem is hardware-related.
 
1 – Run the code to sync the RTC. You just need to run this code with the green button while the RTC is connected to the board (don’t upload this code as main.py). It’s the one in this link:
https://github.com/RuiSantosdotme/RPi-Pico-W-MicroPython-eBook/blob/main/Code/Module_10/10_4_rtc/10_4_1_sync_rtc.py
 
2- Upload the second code to your board (this time upload it as main.py). After copying the code to Thonny IDE, go to File > Save as… and select Raspberry Pi Pico. Save the file as main.py. (Don’t run this code with the green button this time).
https://github.com/RuiSantosdotme/RPi-Pico-W-MicroPython-eBook/blob/main/Code/Module_10/10_4_rtc/10_4_2_rtc_display_time_oled.py
 
Now, it should be running as expected.
 
I hope this is clear. Make sure you follow this procedure exactly as I’ve described.
Let me know the results.
 
Regards,
Sara

Hi,
William: Thanks but as Sara said I don’t think it’s material either. And pull ups have  not improved anything.
Sara I will follow thoroughly your procedure and report here.
Best
Renaud

Hi,
Yes it works. The RTC init program I always installed it correctly.
So what I did wrongly was that I was running the display time program from Thonny. 
Now I can open it, modify it and run it again. Still fine.
Ok, but why was it wrong?
Thanks Sara anyway.
Renaud

Hi.
I think that what you probably did wrong was actually running the code to synchronize the time as main.py.
That code pulls the time from the system. When you run it from Thonny, it gets the time at compilation from your computer. Which is the correct time.
 
When you run it as main.py, it will run and get the time from the RPi system, which was set by the manufacturer on the RPi chip when they built it. In your case, it was 01-01-2021 00:00:01
 
I hope this makes sense.
 
Regards,
Sara

Hi Sara,
Sorry for the delay to answer. That’s myself multitasking!
Yes, what you say makes sense obviously. As I needed Picos with both BME280, RTC, multitasking and server I most probably did something wrong somewhere.
I took everything fresh, taking what was needed again from your excellent book, downloading fresh code and adding only carefully my mods where needed. It works  a treat now.
So I believe you can consider this as solved Sara, with my thanks.
Best,
Renaud

That’s great!
Thanks for letting me know.
I’ll mark this issue as resolved. If you need further help, you just need to open a new question in our forum.
Regards,
Sara