CIRCUIT BOARD 1

COMPONENTS: R14 & R15= 560ohm resistors R13 & R16= 1000ohm resistors L.E.D x2 1.8volts/ 20mA Transistors x2 c547w64 (NPN) Vs=12volts PWM=5volts.

Calculations: R14 & R15 = V/A= 12-1.8/ 20mA= 10.8/.020= 510ohms.

R13 & R16= V/A= 5-.7/5mA= 4.3/.oo5= 860ohms

Beta for transistor found on data sheet.

This circuit has high current flowing from the 12v supply to the collector of the transistors. When the 5v pwm signals come which is low current, it flows through the base to emitter, it opens a gate (so to speak) and allows the high current circuit to flow through the collector to emitter to ground. (or to injectors) or whatever other component you wish to switch on.

To test whether the circuit is working, simple volt drop test can be done across components. Looking at a data sheet for the transistor I found Vce= .05volts and Vbe= .08volts. I also know the L.E.D is 1.8volts. I checked these points with my multimeter and found Vce= 0.04volts for both transistors. Vbe= 0.83 from LED1 and 0.78volts from LED2. The voltage drop across LED1 was 1.86volts LED2 was 2.18volts. I found that all my results were good readings and all within specifications. I also checked the circuit by adding all my voltage drop readings up for each circuit and checking if it match Vs= 12.20volts=Vr14+ LED1+ Vce= 10.28+ 1.86+ .04= 12.18volts= Vr15+ LED2+ Vce= 9.97+ 2.18+ .04= 12.19volts. Vs=5.32volts= Vr13+Vbe= 4.50+.83= 5.33. Vs= 5.32volts= 4.49+ .78= 5.27volts.

When I done my circuit board I had no problems with design, and soldering it all together. It worked properly and first time.

If I had the chance to make it again I think I could make it abit more compact but not to compact that it could heat up fast and fail to work and maybe run earth straight to emitter instead of using jumper wires.