Hi everyone,
This started out with a project from the book Make:Electronics, more specifically the one based on the Jeopardy game where only the fastest player (to press his button) his led goes on. There's a master switch to reset the states and the author mentions he included some capacitors to counteract a false trigger most probably due to switch bounce.
There are indeed false triggers when I leave these capacitors out. But after reducing this circuit to something very simple (but similar) to investigate, it starts getting bizarre.
When I build a voltage divider
Vcc (9Volt)---------10K Ohm---------300K Ohm-------GND
and touch the node in between both resistors with a screwdriver I from time to time get very short voltage drops at that point. My oscilloscope gets triggered and I indeed see a very short voltage drop to zero Volt. Note:
my hand doesn't touch the metal part.
Before this simplification I started with this voltage divider and in between those resistors there was a wire to a spst switch. When I connected the switch (in open position) to ground I got those same voltage drops, say once every 10 times I made the connection with ground. It made no sense to me... the wire is interrupted by the switch?! How can it pull down the voltage?! Even if only for some fraction of time.
I had the same with the original circuit. The master reset switch made contact with ground and the 555 timer trigger input was where I put my 300 K Ohm resistor.
Once I'm back home I'll attach some screenshot and a drawing of what I described.
Maybe it is clear to you? I'm puzzled
Many thanks,
Dirk
This started out with a project from the book Make:Electronics, more specifically the one based on the Jeopardy game where only the fastest player (to press his button) his led goes on. There's a master switch to reset the states and the author mentions he included some capacitors to counteract a false trigger most probably due to switch bounce.
There are indeed false triggers when I leave these capacitors out. But after reducing this circuit to something very simple (but similar) to investigate, it starts getting bizarre.
When I build a voltage divider
Vcc (9Volt)---------10K Ohm---------300K Ohm-------GND
and touch the node in between both resistors with a screwdriver I from time to time get very short voltage drops at that point. My oscilloscope gets triggered and I indeed see a very short voltage drop to zero Volt. Note:
my hand doesn't touch the metal part.
Before this simplification I started with this voltage divider and in between those resistors there was a wire to a spst switch. When I connected the switch (in open position) to ground I got those same voltage drops, say once every 10 times I made the connection with ground. It made no sense to me... the wire is interrupted by the switch?! How can it pull down the voltage?! Even if only for some fraction of time.
I had the same with the original circuit. The master reset switch made contact with ground and the 555 timer trigger input was where I put my 300 K Ohm resistor.
Once I'm back home I'll attach some screenshot and a drawing of what I described.
Maybe it is clear to you? I'm puzzled
Many thanks,
Dirk