Triggering

kurt largo

This may be a stupid question to ask in an engineering forum but can someone offer me a simple explanation of the concept of triggering in electronics?

DublinDilbert

It can mean a few different things.

On a scope you set the trigger level and direction (rising/falling edge), so when the incoming signal matches, the scope will trigger and start recording.

The same is often done in electronic circuits, you design the circuit to do something when an event happens.

FarmerGreen

A trigger starts an event that runs to completion.

As in a gun, you pull the trigger and the bullet comes out the end of the barrel.
Taking your finger off the trigger wont stop it happening.

Like in the scope example, when the signal voltage reaches a certain point the timebase runs until it reaches the end.

In a flash gun, the capacitor is charged to about 400 volts but the tube needs a kick to conduct. So theres a miniature ignition 'trigger' coil that provides a 5Kv kick to start ionisation.

Another example would be in the civil use of explosives for mining or demolition, where the explosive is insensitive to shock, fire, storage conditions etc.
Yet with a certain trigger energy it operates reliably.

Triacs, SCRs, Thyratrons etc all have the ability to switch large currents from a small trigger.

Not a stupid question Kurt, in fact its good fun to give 'experts' brain ache.
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pljudge321

Its hard to know exactly what you mean but here's my stab at explaining clock - edge triggering in an electronic circuit.

Synchronous electronic circuits have a system clock, kind of a like drum beat, keeping everything working at the same pace and in time with each other.

The clock is simply at fixed frequency square voltage varying between two voltage levels. The high voltage level usually represents binary 1 whilst the low represents binary 0.

Each synchronous device in the circuit, such as flip flops, shift registers etc only perform an action when the system clock changes value. If they change on the switch from 0 to 1 in the clock they are positively edged clocked and if they change on the switch to 1 to 0 they are negatively edged switched.

Hope this helps.

kurt largo

Ok thanks for those explanations, I think I have a good idea of what's meant by triggering now

x in the city

or in HDL its normal to use syntax like

always @ posedge clk.....

do something


then all the next operations will be carried out at positive edge of the clock cycle, its to keep things in sync as previously explained.

pljudge321

OP I recommend this program to have a play around with if you want to get a better idea.