Injector circuit.

In practical class today we got handed a sheet with an injector circuit that we had to calculate what value resistors we had to put in the circuit and what the available voltage and voltage drop would be after each

component. We also had to find out how much current flow there will be going through the diodes and transistors and check that reading with the data sheet to make sure we don't exceed the maximum values.

Component list

The components I used in creating this circuit were calculated first on a piece of paper we got handed. Ill show why I picked these particular components under my next heading Calculations. So I used four 470 ohm resistors, two 1N4001or 7 Light Emitting Diode’s and two Bipolar Junction NPN BC547 transistors. I built this circuit first on a breadboard shown in the picture below. 

After building the circuits on breadboards we used a software tool on the computer called Loch master 3.0 were we practiced making the injector circuits on PCB boards. It includes all components al l we had to do was select what component we needed then soldered it to the board. The good thing about this tool is that it allows you to practice building a circuit on the computer were you could easily change things around and figure out were your going to solder the component so that its tidy and evenly spaced so that everything fits properly. After designing the circuit on the computer we used it to build it on an actual board made with copper strips in lines to conduct electricity. The boards are about 50 x 40mm long with holes to insert components to solder. Below is a picture of my board I designed on loch master

Technical explanation of how this circuit works:

Resistors R1 and R3 have one leg connected to a 12v supply and the other leg to the anode side of LED’s D1 and D2 were a voltage drop of .6v is used to turn the led’s on. The cathode probes are connected to the collector terminals of the transistors. R2 and R4 are resistors connected to a 5v modulator, which acts as the ECU sending output pulses to the LED’s, which are meant to be the injectors. In creating this circuit I had to make cuts in between resistors R2 and R4 so voltage can be divided through the resistors to allow a current flow to the base terminals of the transistors. Both the emitter terminals are connected to earth.

This picture shows what it looks like on the other side of the board were soldering the components is done.  

I then made this circuit on to a pcb board.

Calculations

The PD across LED’s 1N4007 is calculated using the formula, pd = ID x VD and A = V/R from ohms law. This formula is used to see if we can use the type of resistor for this diode so that it doesn’t damage the LED.  LED’s have no resistance in them so it important to use the right resistor.

First the amperage flow must be calculated through the LED.

I = V/R therefore voltage is 12 – 0.6 / 470 = 11.4/470 = 0.02A

So now that I have amperage flow I can use this to calculate the power rating of the diode and check with the data sheet if it can handle this amount. Therefore Pd = ID X VD = 0.02 x 0.6 = 0.12 W

According to the data sheet for this led the total device dissipation above 25°C is 2.5W and the average current is 1.0A @ TA 75°C. 

Below is a video of my injector circuit connected to a 12v supply and a 5v modulator connected to the base of the transistor to show how the ecu will change the frequency of the pulse width of the injectors, in this case the LED's. In a car if i started to accelerate the ecu will send signals to the injectors and the injectors will spray at whatever signal they receive from the driver. In my video below i change the frequency high and low which in turn changes how the LED's flash. As i increase the frequency the led's start flashing faster and faster until i have fully increased it, and at this point the LED's stay constantly on and you cant really see them flashing only a tiny but if you look hard. 

Reflection


In making my injector circuit if i had the opportunity to make it again i will and make it better. I will spend more time on loch master designing my circuit so that it looks more professional when I make it. On the other hand I had a fair idea of how the injectors will spray by watching how the LED's flashed.