Timing light trigger

[Kendrick]

Greetings all,

I am new to this forum, so I will be figuring out protocols as I go. I have an electronics education that I have not used much since I could not find a job in my field after graduation.
Long story short.. that means that now I have a fairly strong understanding of Ohms law (and Kirchoff's) and my algebra is pretty good.

That being said, since some of my questions may sound (read: may actually be) pretty stupid, I should be able to get up to speed reasonably quickly.

What I am working on:
I have a conventional automotive timing light that uses an inductive pickup on the plug wires--high voltage, low current pulse-- that triggers a xenon bulb, and is otherwise powered by the 12VDC car battery.

What I want to do is generate an alternative trigger. I do not have a circuit diagram, nor do I know exactly how these work though I have used them for years.

I have tested the signal coming from the inductive pickup on a scope, and it is a noisy (approx) 2-5 VPP AC spike, sometimes 2 spikes in the uS range. 'Noisy' meaning it looks on the scope just like I feel when I accidentally touch the secondary spark itself.

I have other pickups designed for this and their signal looks the same +/- a little Peak voltage, as the one that is connected to the active circuit.

The reason I am doing this ithat I want a synchronized strobe for something that does not provide me with a 20KV spike to trigger it.

I can provide pictures if that helps, assuming I can figure out how to add them on this forum.

What do you think?

 

[unclejed613]

you need a 1.5-2V DC source, whatever method you plan on using to interrupt the voltage, and a differentiator circuit (an RC network with a cap in the signal path, and the resistor from the output side to ground. that will give you the spike you are looking for to trigger the strobe. one example of interrupting the voltage would be, if you are synchronizing with a rotating shaft, is to use a microswitch as the interrupter, and have some kind of raised surface on the shaft to operate the microswitch. there are other means of interrupting the voltage, but the type of device you are going to use depends on what you are trying to synchronize. also, there is a limit with a timing light how fast you can make it flash. there's a 12 to 300V inverter circuit in the timing light that charges up the flash capacitor, and it takes a finite time to charge the cap.

 

[Kendrick]

Cool, Thanks.
I think I get it. I already have a switching DC voltage that I want to use for the trigger, so I don't (in this case) have to mechanically generate it.
It does not need to be as fast as a timing light in my application.

Now I have to go to my notes and look up a differentiator circuit...

Kendrick

 

[Tony Stewart]

Wrap fine wires around T2 core if possible or around gap in large area. V=LdI/dt only needs to be > 12V due to R3:R3! attenuation. and excitation current can be limited by series R to generate dI, L depends on turns and area and core mu, dt is turn off fall time of current. Otherwise hot wire a 0.1 uF cap from your 2V source to SCR1 gate and V- and drive SCR directly.