Nail Coil Gun ECE 445 Project 20 Group

Nail Coil Gun ECE 445 Project: 20 Group: Andria Young, Seth Hartman TA: Ryan May

Introduction • Purpose – To improve existing nail guns • Features and Benefits – Light weight – Portable – No cords, cables, hoses

System Overview Gun Coil

Power • 12 V overall input for boost • 5 V for LM 555, MOSFET driver, and op amp – Provided by 5 V regulator • 2 V for reference voltage in op amp – Used variable voltage regulator tuned for 2 V

Gun Coils • • Critically damped at 20 u. H Diameter as close to nail as possible Glue coil to prevent unraveling Length of coil to match nail length

Circuit Overview Circuit • Oscillating Overall Circuit – Oscillating Circuit – Boost Circuit – Discharge Circuit Boost Circuit

The Oscillating Circuit Design • LM 555 astable timer • Outputs 5 V, 2 k. Hz square wave as input to MOSFET DRIVER • 95% Duty Cycle • MIC 4424 MOSFET driver to drive MOSFET in the Boost Circuit

The Oscillating Circuit LM 555 square wave MOSFET driver signal

Boost Circuit Design • Boost converter using 12 V input to achieve ± 10% 350 V output • Large inductance to increase charging speed • 400 V, 680 u. F capacitor to produce approx. 40 J of energy during discharge • 500 kΩ bleed resistor • Comparator to prevent capacitor from charging above 350 V

Boost Circuit • The inductor – Initial design called for. 02 m. H inductor – Charge was too slow – Tried inductors from. 02 m. H – 50 m. H – Charged fastest at 35 m. H

Boost Circuit • The capacitor – 400 V, 680 u. F – Discharge of ~15 minutes if capacitor isn’t in use – Voltage divider using 500 kΩ bleed resistor as input to op amp – Used variable resistor to tune exactly when charging should stop

Discharge Circuit Design • Sensor sees nail op amp output goes to 3. 6 V • Output of op amp triggers the gate of the SCR • Energy from capacitor discharges into the gun’s coil Sensor

Discharge Circuit • Sensor – Signal from the sensor goes from hi to lo – Use LM 2904 op amp to invert signal • SCR – Output of the op amp triggers the SCR gate – SCR allows energy to be transferred – About 310 A should pass through SCR to gun’s coil in less than 4 ms

Discharge Curve

Discharge Circuit • Solder small resistance where gun coil would go • Charge the capacitor to ~50 V • Block the sensor • Capacitor immediately discharged

Discharge Circuit • What went wrong

Cost • • • MOSFET - $2. 33 x 5 Capacitor - $6. 54 x 3 SCR - $1. 54 x 5 Diode - $0. 17 x 5 Voltage Meter - $5. 00 x 2 Total - $49. 82

Improvements • Ring of capacitors for multiple fires • Lithium Ion Batteries -Lightweight, high energy density

Questions? Thank you!