The heart of the circuit is the integrated circuit (IC) chip. This IC is a microcontroller which comprises input/output logic, a processing unit, and non-volatile memory. This memory contains a program that controls the mode of fire and the solenoid timing. The IC receives input from the DIP switches and tailors the program to produce the desired results. A resistor pack is used to ensure that the IC inputs are set to a strong logical high or 5V signal. Upon throwing a DIP switch, the IC input is pulled to a logical low or to 0V. Since the circuit must operate on 5V DC, the voltage regulator reduces the voltage supplied by the 9V battery to 5V DC. This supply is applied to the VCC input of the IC and is cleaned by a capcitor to protect the IC. The two capacitors tied to the crystal are used in conjuction with the internal crystal input circuit of the IC to produce the timing function. When the IC receives a fire signal from the micro-switch contacted by the trigger, it starts the firing sequence. The IC produces a signal intended to change the state of the solenoid to fire the marker. In order to protect the IC from dangerous inductive charges produced by the solenoid, a diode is placed across the solenoid coil. Additionally, an opto-coupler is placed between the IC and the solenoid. The IC signal turns on the light emitting diode internal to the opto-coupler. The receiver inside the opto-coupler detects the light and completes the circuit to provide a 5V signal to the solenoid. Timing parameters determined by the DIP switches causes the IC to cease the solenoid signal and return the solenoid to the ready state.