Here are two behaviors that I cannot explain:
- I have an ESP8266-12F chip that is connected to an USB-TTL adapter (FTDI) through a breadboard.
The adapter has TX and RX pins connected to RX and TX of the ESP chip directly. The adapter has GND and 3V pins connected to the breadboard so I have 2 rails available to pull up/down some pins of the ESP chip on top of VCC/GND.
Here is first issue: when I plug the black probe of my DMM somewhere in the ground rail, very often the LCD screen of my desktop PC goes black (like off, then on) for a second. Why so? (please remember the FTDI is powered via USB from that PC).
- When I then put the red probe of my DMM to GPIO2 of the ESP chip, it lights on the built-in led of the ESP chip.
Why so? I always thought a voltmeter is "passive", like it does not disturb the circuit I am testing.
I tried with an other DMM: this one does not trigger issue number 1 (screen never flickers), but does light the blue LED as soon as I put the red prob on the pin (eventhough less bright).
Both DMMs are on "V" (DC) position when measuring (not in diode mode or else), auto range.