Powering ESP32/ESP8266 device using OTGW

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rickvanderzwet
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Powering ESP32/ESP8266 device using OTGW

Post by rickvanderzwet »

The schematic page states 'In case you want to power an ESP8266 or similar device from the same power supply, you may want to order these alternatives instead'. Since I am not a electronic engineer I am a bit puzzled by the suggested replacements. The original voltage regulator at IC3, the MC7805CT, is rated 5V/1000mA, how-ever the suggested replacement for IC3 is R-78E5.0-0.5 which is rated 5V/500mA, which leaves me wondering why the suggested alternative seems lower at first glance.

It is also suggested to power an ESP8266, the ESP8266 hardware design guidelines how-ever states it needs to be powered by 3.3V and I cannot find a 3.3V line at the schematic. Also it successor the ESP32 states in the ESP32 hardware design guides a exclusive supported voltage of 3.3V.

Looking at a devkit which is using this MCU, like the NodeMCU, this could indeed be powered by 5V, according to the NodeMCU pinout diagram, how-ever support for 5V input varies per devkit it seems.
RudieO
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Re: Powering ESP32/ESP8266 device using OTGW

Post by RudieO »

The ESP8266 boards as NodeMCU and Wemos mini D1 have a 5 to 3.3 volt regular onboard. Both can be programmed with a USB cable connected only. The basic units need 3.3 volt, and need a USB-TTY convertor for programming. This is the same for the EP32 units. In general the 5 volt power supply is preferred.
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Re: Powering ESP32/ESP8266 device using OTGW

Post by tjfs »

The 7805 needs to be replaced because it's a linear regulator which is inefficient converting 24V to 5V. This works for the PIC only gateway as the PIC draws very little current, however if higher current is required from 5V it makes sense to use a switching regulator such as R-78E5.0-0.5.

It's also possible to start with 5V and use an inexpensive step up converter to generate the 24V supply as the current requirement at 24V is low.

The NodeMCU has an onboard 5V to 3.3V converter as well as a USB/Serial converter which allows it to be used standalone, convenient for programming.

Tim
Last edited by tjfs on Thu Jan 28, 2021 3:07 pm, edited 1 time in total.
hvxl
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Re: Powering ESP32/ESP8266 device using OTGW

Post by hvxl »

I'm very happy to see a user who studies the provided documentation and makes the effort to fully understand how things work.

As tjfs explained, a 7805 converts 24V to 5V by turning the difference into heat. The current going in is the same as the current going out. As the PIC and surrounding circuitry only use a few mA, that causes around 0.1W (19V * 5mA) of heat that needs to be dissipated by the 7805. But when powering an ESP8266-based device, which draws 200mA, that amounts to 19V * 200mA or almost 4W. The 7805 would get very hot very quickly. An R-78E5.0-0.5 actually converts the incoming power into a lower voltage and a higher current with an efficiency of 92%. So it draws 1.09W to produce the 1W (5V * 200mA) on its output. And the loss is back to 0.1W.

You are right that it's not possible to connect a bare ESP8266 to the 5V supply. I have updated the text on the web site to refer to development boards, which include an additional 5V to 3.3V converter.

Correction: After studying the R-78E5.0-0.5 datasheet a bit more, I see that with 24V input and working at 40% of its capacity, the efficiency is around 80%. That results in 0.25W being converted into heat.
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Re: Powering ESP32/ESP8266 device using OTGW

Post by tjfs »

I have one of the Nodo Shop boards and can recommend it.

Tim
Last edited by tjfs on Thu Mar 25, 2021 3:22 am, edited 1 time in total.
rickvanderzwet
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Re: Powering ESP32/ESP8266 device using OTGW

Post by rickvanderzwet »

Thanks for all the comments! It all makes perfect sense to me now.

Thanks for the tip with regards to the Nodo-Shop version, its looks nice, but without the PCB (layout) available and the inclusion of SMD components not as much fun as using the OTGW board.

Time to order some more components and start building :-)
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