Metal to metal touch glitches and 2.4GHz ESP8266 reset - Page 1
Forum section: electronics / rf-microwave

author: RoGeorge
author_rank: Super Contributor
timestamp: March 18, 2021, 03:52:09 pm
content: Ever touched the Rx telescopic antena with a metallic object, or just extend/retract the antenna during reception? There is a very strong and very broad scratching kind of electric noises while doing this, broad enough to hear it in audio, too, no matter the Rx frequency. Even a small and isolated piece of metal (e.g. the rod of a small isolated metallic screwdriver) will still make about the same amount of noises.First, is there a dedicated name for this kind of noise?Then, how do I get rid of it, it happens even when I touch the GND or the Vcc?Asking because I see a lot of resets in an ESP8266 (a chip with a 2.4GHz transceiver chip and a microcontroller on the same die - mounted on a small piece of PCB with nothing but a serial flash and a PCB antenna - the module is widespread and called ESP-01).ESP8266datasheet.ModuleESP-01 Wikipediapage including a high res ESP8266die photo.- the amount of decoupling 0.1uF parallel with a few tens to hundreds uF electrolitic/ceramics doesn't seem to change the situation- adding a few uF of MLCC right on the PCB (so to keep the ground loops closing on the PCB side) doesn't seem to make any difference- powering the module from a 3.3V linear power supply (Rigol DS832) doesn't show any improvement- all 8 different ESP-01 modules tested are resetting the same (yet, all 8 are from the same batch, ordered long time ago from Aliexpress)- changing the firmware doesn't seem to have any influence eitherI know it's a breadboard with wires, but it happens even when the RF side is not transmitting, and it is so sensitive that even the slightest touch with a piece of 2 inches isolated wire will instantly reset the MCU. Never seen something that sensitive.How to filter out the glitches, or what to do so the glitches won't reset the MCU?

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: March 19, 2021, 04:51:07 am
content: Reminds me of a rack mounted digital ranging box, that if you touched it with a key, would reset or glitch.Also if you connected a BNC cable to any jack in the rack it would glitch.Touching with a finger would not do it. Traced the problem to static discharge. The metal to rack "spark" appeared to have much steeper rise time than the finger. Started spraying the carpet with an antistatic spray and problem went away!Cheers,Corby

author: MartinL
author_rank: Regular Contributor
timestamp: March 19, 2021, 05:48:34 pm
content: I'm looking at this schematic for the ESP-01 module:http://www.microchip.ua/wireless/esp01.pdfIt shows a reset pin on the module, connected directly to the reset pin on the ESP8266 chip, with no other circuitry attached.Do you have the reset pin tied to something on your breadboard? If it's just floating, and there isn't an internal pullup in the chip, that would explain this very easily.

author: RoGeorge
author_rank: Super Contributor
timestamp: March 20, 2021, 12:42:02 am
content: Quote from: MartinL on March 19, 2021, 05:48:34 pmEither with the Reset pin to Vcc, or with Reset not connected (has a pull up resistor inside the chip), the ESP8266 still restarts at any metal touch.However, I've noticed the mad restarts only happens when the GND from the USB to serial adapter (so the desktop's GND) is connected to the breadboard's GND. Since the desktop is not Earth grounded and there are all kind of connections all over the workbench, won't investigate it further.Meanwhile I've found out that ESP-01 supports MicroPython, which is very, very nice.It feels very rewarding to use an interpreter, and get instant results at each command, instead to have to compile at each change. It's a whole new level of instant gratification, very rewarding!The bad part is ESP-01 only has 512kB (4Mbit) of flash, which is too little to also fit a file system near the WiFi stack and the MicroPython (the Python interpreter runs on the ESP8266). So I can only type Python code through the serial port, but can not save.The good news is I also found two forgotten ESP-12E modules (from 2016 and not yet powered), with 4MB (32Mbit) of flash. Will flash them with MicroPython and have some fun this weekend. The Python interpreter filling reminds me of the old ZX Spectrum, and its PASIC interpreter, just that this time the whole thing is the size of a thumb nail, and has a 32 bits MCU at 80Mhz instead of an 8 bits Z80 at 3.5MHz.

author: Ultrapurple
author_rank: Super Contributor
timestamp: March 25, 2021, 09:11:05 am
content: What are you powering the thing with?A lot of wall wart PSUs have a capacitive path to mains that leaks a small current and that can be enough to make things interesting.I can usually tell if a PSU is isolated or grounded because when I brush my fingertips lightly against anything metal connected to an ungrounded PSU I feel a slight 'buzzing'. No idea if I'm unique in this but I can detect ludicrously tiny currents. Oddly, the fingertips need to be moving, and within a certain range of speeds.

author: RoGeorge
author_rank: Super Contributor
timestamp: April 08, 2021, 02:54:35 pm
content: Quote from: Ultrapurple on March 25, 2021, 09:11:05 amIndeed, it's intriguing how it feels, and only in certain range of brushing speed. Brushing over with the fingertips feels like the ungrounded (yet mains powered) metal body would be vibrating, and when touched with the back of the fingers over sharp corners or other small contact-point usually it "stings" same as an electrostatic discharge would sting, but continuously.Would be interesting to put a mirror to reflect a laser pointer on a wall, so to see if the metal surface really starts to mechanically vibrate when brushed with the hand (I suspect it wouldn't).About the resets, I've found out they are happening only when the ESP8266 is galvanically connected (through the USB cable) to the desktop PC. When the USB cable is unplugged, ESP8266 doesn't reset no matter the power source (currently powered by an industrial grade wall adapter, capable of 500mA continuous load, has inside a mains transformer followed by a linear regulator).