I will then take the PCB Boards out of the etching tank and rinse them in water to remove any ferryc chloride solution left on the PCB Boards.
Components
After the PCB Board has been etched and the circuit is clearly shown on the PCB Board, I will drill the hole for where the components need to be soldered.
I will refer to my circuit diagram in order to do this. I will need to look at the different sizes for different components.
I will use a mini-pillar drill to drill the holes on the PCB Board, making sure the PCB Board is secured, so that it cannot move before attempting to drill the holes.
After I have drilled all the holes, I will solder my components onto the PCB Board.
I will start off by soldering the resistors, and then solder the capacitors, and the output components, making sure I solder the 555 Timer last.
I will solder the components by holding the lead against the component once I have put it through the hole previously drilled and heat the lead using the soldering iron. I will get rid of any excess lead by using a sucker.
I will solder my components in the following order:
- 2x 10kΩ Resistor
- 0.1μF Capacitor
- Switch (s.p.s.t)
- Light Emitting Diode
- 680Ω Resistor
- Connector Wires – Red and Black
- Battery Snap
- 1mΩ Potentiometer
- Buzzer
- 220μF Capacitor
Testing
Once I have soldered all the components, I will need to test the timer. I will first experiment with the timer, to see if it works correctly. I will switch the timer on and see if the buzzer and L.E.D goes off after a certain amount of time.
After I have found out that the timer works, I will set it at one time using the potentiometer and then I will record the time it takes to go off from switching it on.
I will do this 10 times and compare the results I get to see how accurate the timer is.
Results
Overall average percentage of accuracy:
15.4+2.6+2.6+12.8+5.1+2.6+0.0+0.0+2.6= 48.8
48.8 = 4.88 = 4.88% in accurate
10
100 – 4.88 = 95.12 % accurate
How the PCB Works
The PCB Board has two input devices, which are the switch and the battery. The battery sends an electrical charge to the processing components, such as the resistors, the 555 timers and the capacitor. The current flowing through the circuit fills the capacitor with a charge, and once it is full, it will release the charge. You can control the amount of charge flowing through the circuit using a potentiometer. By using the potentiometer, you can increase or decrease the resistance flowing through the circuit, meaning it will take more time to fill the charge in the capacitor, and increase the time for the buzzer to go off, and the L.E.D to be turned on. Once the charge is full the capacitor releases the charge and the outputs are activated. In this case these are the L.E.D and the buzzer.
Below is a table showing the list of components, showing what they do and their electrical symbol.
Circuit Diagram
After making and testing my timer, I have found out that my timer is 95.12% accurate. I repeated the same experiment 10 times and recorded an average.
My results show that the timer was within 0 – 6 seconds off the required time in some cases.
From my results I found out that my results are 80% reliable, I decided that a 2 second difference from the initial time at 39 seconds was acceptable. A 2 second difference worked out to be 5.1%. In this case 80% of my results were acceptable, making it 80% reliable.
The circuit I have made requires the capacitor to have a full charge before it releases the current through to the two outputs which are the buzzer and the L.E.D. In order for this to happen the battery releases a charge through the circuit. As more tests are done on the same circuit, the resistors on the circuit are likely to heat up. As there is more heat, there will be more resistance.
This means that it will take longer for the capacitor to charge up meaning the time for the buzzer to sound and for the light to be turned on could be delayed.
This could be the case as the times get closer to 39 seconds as we done more tests.
The results in this case are reasonably good, but in other cases may be crucial. This is because the accuracy of the timer depends on what the timer is made to be used for, For example if this timer was used in a microwave, the components would gradually heat up as they are constantly in use resulting to food being burnt.
However if the same timer was used in an alarm clock, the difference of 6 seconds would not much make of a difference.
I had several difficulties while I was making my PCB Board. My main difficulty was that the circuit had been printed as a mirror image, due to the master circuit film being placed on the boards the wrong way round. So it was difficult trying to find out where the components where meant to be soldered. I resolved this problem by referring back to my diagram and noting down where each component was to be soldered, and drawing a new circuit diagram.
Another difficulty I had was that it was difficult to remove excess solder using the sucker. Once the solder had melted it was drying very quickly, and I didn’t have enough time to remove the solder. I resolved this problem by getting another person to suck up the excess solder as I soldered the component onto the PCB board. Overall I think I completed my task successfully, and made the timer to the best of my ability, and got around the difficulties I came across.
I could have improved the results I got from my timer, by leaving a equal gap between each time I tested it. This time could have been approximately a minute long. I would do this, in order to give the circuit time to cool down, making sure that resistance does not give much effect to my results.
In industry, the PCB Boards would be made by using machines. They would have computers to control, the U.V light given to the boards, and would be put in a computer controlled etching tank.
Machines would drill all the holes in the PCB Boards, and they would be produced in a very large amount.
Companies would hire only the best electricians who specialise in soldering to solder the components to the PCB Boards. Major electrical companies might have machines to solder and add components to the PCB Boards, but most companies hire electricians specialising in soldering.
The PCB Boards made in industry would also be very small. Some of the circuits produced are very small in order save space for other boards or components in a device. However the PCB board being very small is not always an advantage. If the boards are small, they will heath up more faster as the components are closer together, and this also means that there will be more resistance in the circuit, which could result to a device not being able to function properly.