2.7V power supply
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I understand that the LoPY4 has a built in 3.3V regulator for the power supply. The specs for the ESP32 and the SX1276 allow for lower supply voltage.
Has anyone attempted to operate LoPY4 (or other pycom devices) at 2.7V? To do so would require disabling the regulator and supplying a regulated 2.7V. Perhaps the existing regulator can be modified to regulate at 2.7V? Does anyone know which regulator is used?
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@sslupsky The regulator is a LM3281. It has a Bypass mode, if the input voltage is too low with a dropout of 60mV at 600 mA. So you can supply your device through Vin.
I had made some test some time ago, and as far as I recall, I went down to 2.5 V. But I did only check, whether the ESP32 was still working. -
@robert-hh Thank you for the feedback. There are no schematics available so I am unsure how to go about evaluating the module at the lower voltage. I have a Pysense as well. I can see the parts on the Pysense and I think the only part on the Pysense that might cause a problem below 3.3V is the SD card. I think newer cards will work at 2.7V though.
I would like to use the module with Lithium Primary batteries that have a typical voltage of about 3.6V. When they are cold though the voltage can go down to 3.4 or 3.3 V. They also have a fairly large impedance because of the oxide layer that forms on the cathode that causes voltage droop during high current spikes.
Are you aware of any issues when operating below 3.7V? I vaguely recall reading a few posts here where people suggested you had to operate with Vin greater than 3.7V for some reason but I do not recall the use case or why at the moment.
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@robert-hh Do you know if the enable pin on the LM3281 is accessible on the LoPY4? If that pin is accessible then the regulator can be disabled.
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@sslupsky Down to about 3.5 V the regulator operates as such. below that, it switches to bypass mode, which is unregulated. The other option is to use an external up/down regulator, like the modules from Pololu S7v8A,, which deliver a stable suitable output voltage in an input range of 2.7 to 11.8 V. If you set that to 3.3 or 3.4 V, the internal regulator is bypassed.
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@sslupsky AFAIK, the enable pin is not accessible.
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