Big ESP32 + SX127x topic part 2


Hi there,
I just wanted to use LMIC with my TTGO32 V2 and I know that for LMIC It’s best to connect:

  • HPDIO1 to GPIO33 (mandatory)
  • HPDIO2 to GPIO32 (option)

Anyone has a picture of the modification done? may help instead of searching on all the pinout everywehre?


‘Searching on all the pinout everywhere’ ?

How difficult can it be? The pinout is only 8 posts above, and at the top. :stuck_out_tongue_winking_eye: Big ESP32 + SX127x topic part 2

You are free to select any possible free GPIO for connecting DIO1 and DIO2.
But using GPIO33 and GPIO32 keeps it consistent with Heltec and the older TTGO’s so less hassle for looking up differences and modifying configuration settings.


Ok, looks like official way is to link the pink part below

I checked an read back this post, DIO for V2 are already connected to GPIO11/GPIO12 check the green ones, so nothing to do in fact :wink:


Really? :wink:

The long red arrows in your picture have to be manually wired.


On hardware view of course, and it’s easier to change 2 lines of code instead going to heat iron and solder 2 wire :wink:


I checked with my multimeter in continuity mode, looks like they are connected as indicated in green on the picture and that’s strange because schematic does not mention that connection except IO12 connected to SD DAT2.


The board PINS are indeed connected as indicated by the green arrows (DIO1 and DIO2), but the green numbers are nonsense. Those pins are not connected to GPIO11 or GPIO12.
This was already documented in the topic start and in my custom version of the pinout diagram.

(Arnas) #418

Hello, I connect LoRa ESP32 SX1276 with LoRaWan. Maybe you know how I can measure data transfer speeds? I measured the distance to the station with ttn map. Maybe someone help me?

(Coeus) #419

The ttn console captures the airtime and the payload size of a particular uplink or downlink - from that you can calculate the speed of transfer if it’s what you meant by speed.

(Vtomanov) #420


I use the Heltec board for some time now and really happy with it the one thing that I can identify still is there any internal connection with voltage divider from the battery to analog pin like in the other development boars with Li battery ?

e.g. I want to be able to measure the battery voltage easily …

(Deux Vis) #421

From what I can understand of the shematic here :

… I would say no.

You can probably hack something together to add it on the board yourself ?

(LoRaTracker) #422

There seem to be quite a few boards of this type which dont provide access to read the battery voltage.

Its a significant omission, to use LiPo batteries safely, and for long life, you need to stop using them when the voltage has fallen to 3.0V or so. This is obviously difficult if you have no provided means of reading the battery voltage.

(Jac Kersing) #423

It is also difficult to stop using power if the board does not provide a ‘switch off’ option so external hardware is required anyway. Why not include a voltage measurement at that point?

(Arnas) #424

Thank you for reply, I mean, How I can measure data transfer rate kilobits or bits per second? Thanks.


Data rates for LoRaWAN are fixed per spreading factor (and low bandwith anyway).

Why would you want to measure the transferrate?

(Sami4) #426

As i can see from datasheet SX1278 supports OOK tx and rx mode, but i haven’t found the right way how to do this. Are there any sample sketch how this can be done?

(Biermi) #427

i have a Heltec 868 Mhz V2 (Pinout: and an old Garmin Geko 201. The Garmin Geko has a RS232 interface which i want to connect to the Heltec Device. I use a MAX3232 Converter for RS232 to TTL and the Geko sends its data as MNEA 0183 format. I have found a simple GPS library ( to decode the data. My problem is, that the library uses soft serial to get the data from any pin (4800 Baud) on the ESP. But soft serial is not available for the ESP32 and so i think i can use hardware serial, an ESP has 3 UART so it should normally no problem, but which pins can i use? i have read the docs that Serial1 uses pin 9 and 10, but this pins are not existing on the Heltec board. Serial2 uses pin 16 and 17. Pin 17 is also used by the oled display, so it can be a problem to use this pins. I guess Serial with pin 1 and 3 will be used for communication with the usb port for example the Arduino IDE monitor so not usable for my use case. Has anybody an idea what can i use or do?

Kind regards


Take look at the LABS -

(LoRaTracker) #429

With some limitations you can use any of the pins for the GPS TX and RX, just define the pins;

#define GPSRX 17
#define GPSTX 16

And initialise the hardware serial port like this;

GPSserial.begin(9600, SERIAL_8N1, GPSTX, GPSRX);

(Tonino Tarsi) #430

I did some tests and looks like that the battery is not charged when solar panel is connected to 5V pin. works file with USB ( and diode )