Experiment - Injector circuit

Component list:

 - Power supply: 1 from battery is 12V.

                 3 & 4 from ECU is 5V it can control LED frequency and bright.

                 2 is ground.

 - Transistors: I choose two of BC547 NPN: Vbco = 50V; Vces(Vbe=0) = 50V; Vceo(Ib=0) = 45V; Vbeo = 6V; Ic = 100mA; Icm = 200mA Ptot(TA<25°C) = 500mW(derate 4mW/°C above 25°C); Tstg = -55 to 150°C. Emitter-Base breakdown Voltage = 6V; Icbo= 15nA; Vce(sat)=0.25V(Ic=10mA,Ib=0.5mA);Vbe(sat)=0.7V(Ic=10mA, Ib=0.5mA); fT= 250MHz

 - LED: I choose two LEDs one is red another is yellow, from LED datasheet I know LED voltage is 1.8V and amperage is 20mA. But I searched web the yellow LED has a different of the voltage drop is around 5V.

 - Resistors: I used four resistors in this circuit two before the LED positive I called R14 & R15 and the other two before base of the transistors I called R13 & R16. From calculations I know:R14 & R15 = V(12V)-V(LED 1.8V)/A(LED data sheet 20mA) because these are parallel circuit so the voltage same, and from the LED data sheet told us 20mA should flow throw it. So I can calculate how big resistors should in this circuit. R14 & R15 = 510ohms, so I can take below 510ohms of resistor in this circuit. I choose two 470ohms resistors for each LED.

R13 & R16= Vs(5V)-Vbe(0.6V)/Ib(20mA), so R13 & R16 I choose 2200ohms resistor.

When I build this circuit I got a problem from LED, because I choose a LED doesn't work before I use. So when I build it and check the circuit connection all good, than I connect the power supply. But only one LED can bright, than I use multimeter to check available voltage and voltage drop from each component, I found the disconnection LED, so changed it. Than the circuit work well. After I checked available voltage and voltage drop again, when I read from multimeter I find the different colour LED has different voltage drop and available voltage, than I asked tutor also searched from Google, I got the reading is: Green & Red LED about 2.2V; White LED about 3.5V; Yellow LED about 5.5V. 

The fuel injector circuit when the engine start injector push throw the fuel into intake valve to the cylinder, when goes to high speed the fly wheel turn crankshaft fast and the piston move up and down fast also engine need more fuel and air. So it made injector open more frequency than idle speed. In this circuit I know if I use high resistance of R14 & R15, the LED will be less bright. It is mean high resistance block lots of current so LED couldn't get enough current throw, also mean injector cannot open very well. If use this experience to the real car problem I would know if I step on fuel pedal but the car couldn't got high speed, and the problem may be from injector leaking. So we can check the voltage drop from each components, if before injector has high voltage drop it will be the high resistance. From other side, the power supply from the ECU to control the frequency of the injectors, when we push down the fuel pedal it will told ECU the car will go fast and ECU will change the frequency for injector.

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