I’ve been using the TTGO T-Call ESP32 SIM800L for a few weeks to send a text messages containing my battery voltage from my solar panels to my mobile a few times each day. It has worked perfectly until I decided to tidy up the circuit and power the module from a 24 to 5 volt buck converter which I have connected to the 5v pin (the 24 volt from the battery is connected to one of the ADC inputs via a voltage divider). I’ve checked the T-Call circuit diagram and I thought the 5v input should be OK but I could not see if this is the same as the USB connector input.
On checking the dead module, if I power it from the USB port, all the 3.3v pins now read 5v and there is no flashing red light so I assume the voltage regulator has blown.
Do you have any thoughts before I fry another module.
Thanks for your excellent projects and advice.
I think you can power the SIM800L with 5V on th 5V pin, but I haven’t looked at the board diagram.
However, what might have caused the issue is the battery connected to the ADC inputs. I think these pins are only 3.3V tolerant, so check the maximum voltage output out of the voltage divider.
That’s helpful, I’ve used the formula vout=r2/(r1+r2)x vin which appeared ok.
I think my best plan is to protect the sense voltage input with a zener diode at 3 volts and use a linear regulator rather than a buck converter to power the module. I’ve noticed that when I reduce the voltage input to the buck converter, it outputs 18 volts which is more than enough to kill the module.
Yes, 18V will kill the module.
There are some buck converters that you can regulate using a small potentiometer. If you are not careful you may get more volts that your board can handl.
Good luck with your project.
I’ve changed for a fixed voltage 5v converter and the device has worked perfectly for 4 days using the 5 volt pin to provide power. Thanks for your help.