ESP32 Forum

Hi,
I want to use the ESP32-WROOM-32E Module to make a simple battery operated device, which transmits a 16 byte hex string when a button is pressed. Only Bluetooth to be used, no Wi-Fi. Short press of the button should wake up the device and have it transmit this 16 byte string once every second. A long press of the button should put the device into sleep or hibernate mode.

1. Can this simple code be stored in the on-board 4MB SPI Flash or is a SD card required for the code storage ?
2. This device should act like a BT beacon and the 16 byte transmission should be receivable by any other BT device - say by another ESP32-WROOM-32E Module or a phone. Is this possible ?

Thanks !

Hi Synectix,

1. You won't need a SD card for this.
2. In summary; yes, it should be possible. This page explains it pretty well.

Thanks !
Another newbie question
The link given by you for BLE on ESP32 uses the Arduino IDE as an example.
I assume I can the ESP32-IDF on my Windows 10 Laptop to download the application to the WROOM-32E Module, correct ?

Hi,

you can use ESP-IDF to build to build the app and flash it onto the WROOM-32E Module.
Be sure to check out the bluetooth examples in ESP-IDF.

Hi,
I installed the ESP-IDF successfully, started with the Eddystone project, copied all files into a project folder (discovered the hard way that I need to copy the 'raw' file..) and 'build' the project.

The build task, while it is processing, seems to be showing the number of obj files being used, which started from 04/1165 and after 30 minutes was still at 65/1165 ! Why would the 'build' task take such a long time ? At the rate at which it was going, it would have taken 10 hours to build !!

I did not see any errors, except the "Missing PERL_EXECUTABLE" error, which as per your answers elsewhere in the Forum is not relevant and can be ignored.

I closed all other applications on my Laptop, the Task Manager showed very nominal usage of CPU, Memory & Disk, my Laptop has i5 CPU & 8GB of Memory...so, what am I missing ?

I had to terminate the build process as it did not make any sense to continue at this rate !

Hi Synectix,
the slow compile speed may be due to your antivirus software.
Please reinstall IDF-tools using the installer.
The installer registers the tools as Windows Defender exclusions to improve compile speed. After that, check if the issue persists.

If this doesn't fix the issue try disabling your antivirus software and post which antivirus you are using.

Thanks. Problem solved !
I am certain that I had enabled the "Windows Defender Exclusion" checkbox when I installed it the first time too.
Anyway, I uninstalled the esp-idf and re-installed with "Run as Administrator" option.
Now the eddystone project's build time is about 4 min 30 seconds !

I am yet to get my hands on the Modules themselves.
Hence, I will have more questions next week, when I start using the modules.
Thanks again

Another quick question on the power supply for the WROOM-32E Module :
The Data sheet for the Module says Operating voltage range is 3.0 to 3.6V.
So, will this Module be able to work off a 3V Button Cell, for BLE application, with Wi-Fi Disabled and very limited broadcast activity on BLE ?

The ESP32 chip itself has Operating Voltage from 2.3V. So, why this 3V limit for the Module ?
Is this because of the SPI Flash ?

Hi Synectix,
The ESP32 datasheet in section 2.3 Power Scheme states:

When a battery is used as the power supply for the ESP32 series of chips and modules, a supply voltagesupervisor is recommended, so that a boot failure due to low voltage is avoided. Users are recommendedto pull CHIP_PU low if the power supply for ESP32 is below 2.3 V. For the reset circuit, please refer to FigureESP32-WROOM-32 Peripheral Schematics, inESP32-WROOM-32 Datasheet.

and

The operating voltage of ESP32 ranges from 2.3 V to 3.6 V. When using a single-power supply, the recom-mended voltage of the power supply is 3.3 V, and its recommended output current is 500 mA or more.

A button cell is not entirely suitable. Its voltage is too low and the current capabilities aren't really suitable for the ESP32. More on this here: https://www.esp32.com/viewtopic.php?t=975

OK, Thanks for the information !
I had sort of given up on using the CR2032 3V button cell for the ESP32 module anyway.....but, just wanted to be sure