Big ESP32 + SX127x topic part 2


Maybe you can visit me this weekend to test some of my antenna’s? :grin:

(Coeus) #392

Anyone has successfully configure a Heltec WiFi 32 board 868-915Mhz to operate on AS923 and connect to TTN through OTA?

(Tonino Tarsi) #393

A simple question. I have TTGO V1 LoRA board.
Is the charger for LiPO or for LI-ION battery ?


Should be fine for both Li-Ion and LiPo (but not for LiFEPO4 (Lithium Iron Phosphate)).

(Tonino Tarsi) #395

Thanks. So a more difficult question :
I will power it with a solar panel and battery. Now, I have connected the solar panel to the usb conector.
Could I connect the solar panel direly to the 5v pin ?

(Kalon33) #396

Dear all, I’m trying to put pin 35 of TTGO V2 board to gnd level in order to drive a card, using:


But unfortunately, that failed, and when board is in deep sleep, pin is still not at that level.

Do you know how I can fix that?

(Edzelf) #397

Pin 35 is input only.

(Kalon33) #398

So how I can find this and which ones may I use for it?

(Edzelf) #399

this may be a good starting point.

(Kalon33) #400

Sure, I already read this and the pinout diagram, but I didn’t noticed that fact, that’s why I’m asking that to you, as it seems you have a better knowledge than me about this board or boards in general… I planned to use 36, 39 and 34 to retrieve data from a MICS-6814 sensor (for now, I don’t know how to deal with it when it is not I2C interfaced), and need a way to turn on/off the step up power regulator that powers it, switching a pin on the power regulator from +3,3V to GND.

(Edzelf) #401

Unused pins are 0,2,4,12,13,15,16,17,18,23,…


From the ESP32 Technical reference v3.0 p45:

Note that the I/O GPIO pads are 0-19, 21-23, 25-27, 32-39,
while the output GPIOs are 0-19, 21-23, 25-27, 32-33.
GPIO pads 34-39 are input-only.

I had not bumped into this yet and not seen an ESP32 pinout diagram mentioning GPIO 34-39 are input only.

There appears to be no extensive documentation for the ESP32 Arduino Core but you can find documentation for the ESP32 here:


I just uploaded a new version of the TTGO v2 pinout diagram: TTGO LoRa32 V2.0 Pinout v2.2.pdf (2.4 MB)


I would expect so, but difficult to say because I have neither the board nor the schematics.
It is common that a diode is placed in series with the USB power (as part of the board design) to prevent current flowing back to the USB port when the board is powered via a 5V / ‘Raw IN’ pin.
You should use a diode in series with the solar panel to prevent current flowing back from the battery when the panel is not producing (enough) energy.
Also take care that the output voltage from the solar panel does not exceed the limits of the voltage regulator on the TTGO board (also when you feed it from the solar panel via the USB port).

(Tonino Tarsi) #405

Thanks very much. Very clear and useful.

(LoRaTracker) #406

You need to add your own pullups too.


Studying the ESP datasheet and technical reference I found no mentioning that GPIO34-GPIO39 cannot have pull-ups or pull-downs. What I did notice is the following:
After a reset input is disabled for the following GPIO ports:
GPIO25, GPIO26, GPIO32, GPIO33, GPIO34, GPIO35, GPIO36, GPIO37, GPIO38 and GPIO39.
(GPIO state can be preserved for low power purposes which can possibly have an effect on this.)

If I am correct input disabled does not implicitly mean that output is enabled (tri-state logic), and pull-ups or pull-downs can only be defined for inputs. So when after reset input for above GPIO ports is disabled so will their pull-ups and pull-downs.
But it may still be possible to (re)enable internal pull-up or pull-down for these GPIO’s when explicitly enabling input for these GPIO’s after a reset. (This is an assumption, I haven’t tested it.)

(LoRaTracker) #408

The requirement for pullups has been reported on the expressif Github as an issue a couple of times at least;

I found much the same, so I have added the external resistors to a board I was designing.

(LoRaTracker) #409

From the ESP32 datasheet;

"GPIO pins 34-39 are input-only. These pins do not feature an output driver or internal pullup/pull-down circuitry. The pin names are: SENSOR_VP (GPIO36), SENSOR_CAPP (GPIO37),