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Registered Member #2648
Joined: Sun Jan 24 2010, 12:45PM
Location: Australia
Posts: 291
Hey
I just designed this trigger logic for my coilgun and would like to share it.
Overveiw: This is circuit is designed to turn on/off an IGBT in a coilgun from input from a Phototransistor or similar device. It turns on the (first) IGBT only on trigger Positive edge. Once on the IGBT will be high until the Phototransistor Negative edge (once projectile as passed phototransistor); it is unaffected by trigger held on, trigger off, trigger bounce etc. Once output is low again trigger can be turned on.
Logic Schematic:
Sorry for the bad diagram, Yenka is the only program I had at hand, but you should get the idea.
Operation: This consists of two positive edge JK flip-flops, ICa processes the trigger input, and ICb processes the phototransistor input. When output is low ICb is ignores the phototransistor because both J and K are low. When ICa gets triggered it will switch inverting out high because J is high or if J+K are high too it will toggle to on. ICa inverting out low activates ICb asynchronous set, turning ICb output (IGBT output) high. ICb output high through an inverter turns ICa asynchronous reset low, locking ICa low. ICa will then ignore the trigger input. ICb will now be monitoring the Phototransistor input because ICb J+K are now high. The IGBT turns on, pulling the projectile. The projectile passes the phototransistor creating a positive edge on ICb clock input. ICb output toggles off, turning the IGBT off, unlocking ICa and it is ready for the next round.
Multi-Stage: It is possible for this to be modified to drive a multi-stage coilgun. To do this the same circuit is attached to the first stage circuit by connecting the trigger input to the first stage IGBT output through an inverter. The second stage will be triggered when the first stage goes low (when the projectile passes the first stage). it then behaves just as the first stage. More stages can be added just as the second stage is added; the trigger input is replaced by a connection through an inverter to the IGBT output of the previous stage.
Issues: I can currently see one problem specific to this circuit: 1. In multi-stage the first stage can be retriggered if another stage on. This could be solved by adding extra logic
Any comments, suggestions and criticism is welcome I plan to make a better schematic, add a multi-stage schematic and truth table if anyone is interested
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Coilgun Logic
