ebay 103c8t6 oled, nrf24, esp8266 + empty pads

[democles9308]

See on his website http://www.brokking.net or his YouTube channel. He did a series on a drone with an arduino, he is now preparing a series on a drone with STM32F103-board. Really instructive.

[zmemw16]

bad site, re-routes to www dot booking dot com

[mrburnette]

http://www.brokking.net/ymfc-al_main.html

[zmemw16]

cheers ray.
there's a space in the link - missed it completely.
srp

[democles9308]

Sorry for th typo in the link, updated it.
https://www.youtube.com/playlist?list=P ... LQVkDFHbxC For his videos on his STM32 drone project.
D

[electrobling]

One possibly strange thing I noticed - the VBAT pin has diodes on it. One to the battery, one to VCC_3.3V. It looks like they want to relieve the battery when the power is on. But looking at the processor data sheet, it looks like it has provision for that internally. I haven't seen other boards that have a provisioned battery backup, so I don't know if it is really needed or if it is a standard practice. With simpler boards, I hope I can just connect the battery to VBAT and not worry about it.

[flodejr]

One possibly strange thing I noticed - the VBAT pin has diodes on it. One to the battery, one to VCC_3.3V. It looks like they want to relieve the battery when the power is on. But looking at the processor data sheet, it looks like it has provision for that internally. I haven't seen other boards that have a provisioned battery backup, so I don't know if it is really needed or if it is a standard practice. With simpler boards, I hope I can just connect the battery to VBAT and not worry about it.

I think the diode to VCC is to prevent the backup battery from powering the entire circuit when the main power source is removed. The internal diode was meant to protect against reverse voltage whilst the external added diode to VBAT may be a zener diode clamping the voltage to 3.3V.

[electrobling]

It is hard to find boards that have an on board battery to seek guidance from. Most have VBAT as an external pin connection, or connected to VCC. But the Mini STM32 V3.0 and the LY-M3S STM32F103ZET6, which both have on board batteries, both have VBAT connected directly to the battery, with no additional circuits.

It will be a few weeks before my boards arrive, so I can't try it, but it seems to me that the processor must adequately isolate the battery when power is off, and the designers of this board just got paranoid and threw the isolation diodes on without testing.

See 5.1.6 Power supply scheme on page 36/117 of the data sheet.

I'll buy the explanation of battery reverse voltage, as it is possible to stupidly insert a coin battery backwards. However, I think the chances of a higher voltage than 3.3V appearing there are almost nil, so although it is a bit of mind reading without proof, I think the intention was to supply voltage from VCC in the absence of a battery. In other words, confusion. Or it was cloned from some other device.

Edit - this board does not have a removable battery, it's soldered in. I think the ability to check polarity is assumed with the ability to solder.

Anyway, it is important to me because a working RTC is a big part of my plans.

[zmemw16]

istr @someone had blue smoke from a vbat pins shorted to usb vcc ?
srp

[electrobling]

I read that one. I can't find in now, but while looking for it, I noticed that the CZ mini STM32F103VET6 has the same diode circuit. Hmmm.... now I'm really wondering...

Edit - I should really download the other processor data sheets and compare. None of those are 103C version.