Hi guys, I couldn't find anything on web regarding this problem which I believe is quite general.
I have build (on a breadboard) a circuit with ATMega8, LCD, couple of shift registers and 74HC08, 74HC00 to control the shift registers clock. I have connected LEDs to my shift serial-to-parallel register to observe it's state. Whenever I touch the groung of the circuit on the breadboard with a pinsette held in a bare had, the shift register goes crazy (it shifts by few bits). ATMega is NOT reset or anything, it stays in the correct state, LCD doesn't display garbage, it's just the 74HC00+74HC08+74HC164 circuitry what is "sensitive to touching". I also have intermittent problems programming the ATMega, when the programmer reads random device signature, but after a while this settles and I can continue working. No relays or motor or other inductive load connected.
I connected all unused NAND and AND gate inputs to ground.
The circuit is powered by a switching network adapter 6V, with 7805 and a capacitor connected between it's output rails. I don't have 100n capacitors in parallel with my 74xxx IC's.
I was wondering how this can be? Maybe if you tell me how this "phenomena" is called I could google for it myself, but most of the EMF articles talk about inductive load. I could understand that touching an unconnected pin of CMOS IC could do this, but responding to touching GND seems really weird to me :(
Any ideas or hints?