Saturday, October24, 2020
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Which ESP32 Should You Pick

There are many versions. Which one is right?
And how should I power it?



There are many versions of the ESP32. Picking which of many incomparable development boards was a fundamental decision. Changing would be a complete redesign of the Printed Circuit Board (PCB). I used a LOLIN32. That might seem odd as the board is listed by its developer as obsolete. The newer one is the LOLIN D32. One might ask why I picked an obsolete board and more generally why I picked a board with a battery power option when I am not using battery power but rather boat power.

Why pick a battery power unit complete with local LiIon battery charger? A more straight forward choice might be the ESP32 DOIT DevKit v1 which is very widely available. It turns out that the answer is very simple. Units that are going to run on a small LiIon battery are designed to use very little power. Most notably, the DevKit unit has an LED that is on whenever power is applied. That LED draws little compared to the ESP itself but since in this application the ESP will be off almost all the time, the LED would be the thing that would produce the most drain on the boat's battery should either shore power fail, or as is the case with my Dutch friend, there is no shore power.

Why pick an obsolete unit? Just now I was looking for the name of the unit I did not pick, the LOLIN D32 and I could not find a single place that advertised selling it. I found many many sources for the LOLIN32 and that is why I decided it was the best choice. It is an open source design so apparently many suppliers are making it. The heart of all of these is a module made by Espressif so really no matter which one you buy, you are getting the same ESP32. Just the support chips, LED, battery charger, are different.

How did I power the module? One might think that taking a 12-14 volt boat battery and using a linear regulator to bring the voltage down to 3.2 volts is wasteful. Such a regulator is going to be at best around 20% efficient. It turns out that because the unit is almost always off and drawing almost no power, overall this is the lowest power way to supply the needed voltage. The key specification is not efficiency but rather quiescent current. Switching regulators are efficient when you need a lot of current, but very inefficient when they are supplying almost no current. The best thing is to use a low power 3.3 volt regulator such as the TC1262-3.3VAB. It has a quiescent of close to zero (0.13mA) and will supply the same 500mA that the boards onboard MCD1826 can supply but with the advantage of not having to drive the battery charger. I opted to use a 5 volt regulator before I figured all this out. It draws very little power but it does supply the onboard battery charger which waste a bit of power that would not be wasted if I had used the 3.3 volt versions.
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