Blog 3 Injector circuit board

What we are doing here is to build a Injector Circuit Board which the diagram is shown below

Calculations:

Assume the current flow through both LED is 20mA from range 10mA-50mA

  R14=R15

=Vs-Vled/Iled

=12-2/0.02

=500≈470R

Because we want the transistor to be in saturation mode,so we need the current going through Base close enough it's minimum value.Assume current Ib=2mA

  R13=R16

=Vsingal-Vbe/Ib

=5-0.7/0.002

=4.3/0.002

=2150≈2k2

So R14=R15=470R and R13=R16=2k2

Components list:


2x 470R resistors
2x 2k2 resistors
1x 5mm yellow LED and 1x 5mm red LED
2x BC547 transistors which the datasheet is shown below:

This is how I designed the circuit from lochmaster

How the circuit works and why is it called Injector circuit?

This circuit is basically using transistors to switch device on and off.

There is one separate signal input for each transistor and LED, when a 5v supplies to one of them,the transistor switches on it's controlled LED and it should flashes fast or slow by adjusting the frequency of the signal current.

When use this circuit in a car injection system, LEDs are actually injectors. Each injector has one transistor for switching them on and off, a battery voltage will be supplied through the injectors to all the Collector terminals of the transistors by connecting them in parallel and a voltage signal from ECU will be connected to Base terminal, the ECU will turn on the circuit and energize the injector by grounding the Emitter terminal to each transistor by the pre-programmed order.

This is why it is called an Injector Circuit.

This is the actual circuit I made

How to test the circuit?

To test if the circuit is working or not, connect 12v to the red wire which is the power supply to the circuit and ground the black wire.Then connect 5v signal to yellow wire which is the Base terminal to LED1 which is the yellow LED and it should lights up, process the same thing to LED2 which is the red LED. Also the LEDs should flash when vary the 5v signal frequency.

Results:

I made the circuit going in two tries

On the first try,the green LED was working but not the red one which eventually I found out that I have done the LED and resistor in wrong location which was the resistor sit behind the LED,that way the current will flow through From LED to resistor which current is supposed to be flowed through from resistor to LED

On the second try after I switched the position of the resistor and red LED,the whole board works well as it should be.

Reflection:

This circuit is fun and easy to start with, I was planing to make it work on the first attempt but I didn't, the reason I did not make it work was because I did not design it well and the circuit was a mass so it is not easy to tell which component is in the front or which one is at the back.

If I have the chance to make this again, I will improve the way how I design it on the lochmaster and make it looks nice too, a more clearer circuit will be hard to make a trouble and easy for fault finding as well.

References:

auto101.com

wikipedia

Unitec Moodle

Vijay Naidu