Big ESP32 + SX127x topic part 2


Another option to work around the issue (not a fix) may be to throttle the current usage during power-up, i.e. gradually start initializing/using Wifi and Bluetooth interfaces with some pauses in between from startup.

This may help prevent the voltage sink during start-up from battery that causes the brown-out.

(Verkehrsrot) #252

The question here is probably: How is the power circuit on the TTGOv2 board designed?
I assume that the 3,7V battery drives some kind of step-up/step-down circuit, and maybe this circuit lacks of peak power.

350mA spikes @5V is 1,75W peak. This shouldn’t be a problem for a LiPo cell?

(LoRaTracker) #253

Lipos have a very low internal resistance, so should handle such current spikes easily.

So what does the VCC power rail, 3.3V, to the CPU look like on a scope ?


Unlikely to work, but try putting a 100uF cap across the 3.3V / ground.
Chances are, the power circuit is similar to a feather board as per here
In this board there are 2 separate chips (circuits) involved with power.

  1. MCP738312 - Battery charge circuit (5v Vbus to battery Vbat)
  2. AP2112 - Power supply Circuit - Linear Regulator - 2 inputs of battery Vbat and 5v Vbus, with a regulated output of 3.3v

N.B. Make sure you check the lipo battery voltage and 3.3v supply when not connected to USB - you may have a bad battery?

(esatkaraer) #255


I am playing with the TTGO V1 OLED and I am trying to make GPS work. I ordered an GN-801 from Aliexpress.
I could not find good examples for this particular GPS module because this one has 6 pins ; GND, VCC, TX,RX, PPA and EN.
I connected everything but PPA and EN. I am not sure what to do with these. Here is what I have :
on top:
#define GPS_RX 23
#define GPS_TX 17
HardwareSerial GPSSerial(2);
GPSSerial.begin(9600, SERIAL_8N1, GPS_RX, GPS_TX);
while (GPSSerial.available() > 0)



It might help you to take a look at post 191 in this topic or search the LABS page for my node example.

I think PPA would be a pulse per second output and the EN pin is internally pulled high, so both can be left disconnected

(Mirtcho) #257

Issue fond.
esp_deep_sleep_start() - causes spikes in some GPIO - e.g SPI SCK pin, at the same time GPIO14(LoRa RST ) seems to be hi-Z -> spike occures in this pin. The result is reset SX1276.
Temrorary I added pull up 2KOhm and SW reinitialize of SCK as input.

maybe graceful stop of spi before esp_deep_sleep_start() coud be the final solution. Needs to be tested . Sorry No time for it.

(Mirtcho) #258

Just another disappointing result from these boards.
I have tryed two Heltec. In term of coner range they behaves similar.
Test setup – Transmitter Raspberry pi at home with decent Sx1276 module. –W=125KHz SF=11

  1. Node 1 – Heltec board #2
    – at home two floor difference - packet RSSI -95dbm
  • 100 meter -110…115dbm after 300m problems
  • Best achived distance – 500…700meters. min achived RSSI -123dbm
  1. Node 2 – Heltec board #2 – similar to Node 1
  2. Node 3 – the same good quality module as transmitter at home Arduino atmega2560 SPI
    a. At home RSSI -48…-49dbm
    b. 1km – RSSI -100dbm
    c. 2km at wet wood area - -120…-122dbm
    d. 11.15km – in open agriculture are
    Transmiter was staying the same an test was done at the same time interval. Antenas ware the same groundplane – swapped between nodes.

(Pixelchain) #259

Used the same GPS module, didn’t connect the PPA and EN at all. It worked.
I’ve used pins 35 and 34 for RX/TX on the TTGO V2.0

The TX of GPS connected to 34
The RX of GPS connected to 35 (I’m not using it currently but you could use it to configure the module over internal messages)

Take care the colors on cables are wrong. Use the text writen on PCB.
Red is GND
Black is VCC and so on