TTGO T-Call ESP32 SIM800L – Power Supply Question

Q&A Forum › Category: ESP32 › TTGO T-Call ESP32 SIM800L – Power Supply Question

Peter Ashford asked 4 years ago

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.
Peter

Question Tags: TTGO T-Call ESP32 SIM800L

5 Answers

0 Vote Up Vote Down

Sara Santos Staff answered 4 years ago

Hi Peter.
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.
Regards,
Sara

0 Vote Up Vote Down

Peter Ashford answered 4 years ago

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.
Peter

0 Vote Up Vote Down

Sara Santos Staff answered 4 years ago

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.
Regards,
Sara

0 Vote Up Vote Down

Peter Ashford answered 4 years ago

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.
Peter

0 Vote Up Vote Down

Sara Santos Staff answered 4 years ago

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