MODIFIED BEAM RESTORE CIRCUIT EXPLAINATION

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Q2 is normally conducting when it is getting beam. To arm the trigger, the momentary switch wired to the gate of SCR4 is pressed causing SCR4 to conduct to ground, which illuminates the green LED. When SCR4 conducts, it acts like a short circuit and robs all current from the RED led and other components. As the beam is broken with the projectile, Q2 stops conducting causing SCR4 to also stop conducting and the green LED goes out. Since Q2 is not conducting, the Red LED is also off. When the projectile passes and the beam is restored, Q2 begins conducting again. But now since there is no new gate signal to SCR4, SCR4 does not conduct. With no other way for the current to go, it heads through the red LED and other components. Now the red LED is illuminated and Q4 gets signal to it's base and begins to conduct to the gate of the main SCR, SCR3. The 2k Ohm resistor above Q4 is adjusted so that SCR3 doesn't get a false positive or negative signal. When the main SCR gets gate signal, it conducts the charge on the capacitor throught the coil, until the capacitor is discharged. When the SCR stops conducting the coil passes it's stored charge (inductance) through the bypass diode (D3) and disapates the rest of the stored energy. The 2K resistor between the two triggers is an isolation resistor that prevents the restoration of the gate signal into trigger one from trigger two's power (since trigger one always goes off before trigger two).

Last updated: 6/22/02
Copyright 2002, Greg Miller
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