[sdiy] what is trigger signal?

[Florian Anwander]

HI Alex 

> what is trigger signal?  just a surge of voltage?  how is it different from
> a gate signal?
Though everyone wrote, that a trigger is a short signal, this is wrong ... ok
not exact.

A trigger marks a timestamp, a gate marks a length of time.

On principle it is a definition, how a input recognizes a levelchange of a
digital signal. A trigger marks a timestamp by a change of a voltage, usually
from 0V to 5V  OR(!) from 5V to 0V. The first one (0to5) we call a positive
trigger, the latter (5to0) is a negativ trigger. 


^ voltage
|
|
|                            __________________________________________
|                           |
|                           |
|___________________________|
|=====================================================================>time
Positive trigger marks this ^ timestamp


^ voltage
|
|
|___________________________
|                           |
|                           |
|                           |_________________________________________
|=====================================================================>time
negative trigger marks this ^ timestamp


The following is a gate which represents the movement of a key.


^ voltage
|
|
|          _________________________________
|          |                                |
|          |                                |
|__________|                                |_______________________
|=====================================================================>time
           ^                                ^
           |                                |
           |                                |
           This is a tigger                 |This is a trigger too

The begin of the gate is a positive trigger that marks the timestamp of the
keypress, the end of the gate is a trigger that marks the timestamp of the
leaving the key.



So if something says it needs a trigger, only the sigificant voltage transition
is relevant. When and how the voltage "movement" back is done, doe not matter.
So you can use a short peak signal (as the others mentioned).

Florian

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