Skill level: * * * ADVANCED
Project constructed on track board.
Precision soldering required to avoid solder on one copper track coming into contact with an adjacent copper track.
This circuit contains one light-emitting diode which flashes on and off. The rate of flashing can be varied. The circuit diagram is shown below.
close-up of IC1 showing
the notch and recessed dot
next to pin 1
6. Cut a piece of link wire and, using pliers, bend it to form a shape like a staple, as shown below. Push this staple through the top surface into holes B8 and I8 and bend the ends of the wire link slightly apart. Solder the wire link to the track surface.
Take a second piece of link wire, push it through holes A9 and E9 and solder.
Take a third piece of link wire. Use pliers to bend it so that it fits into holes C10 and D15 and solder (this link connects pin 2 and pin 6 together).
Take a fourth piece of link wire, push it through holes A15 and B15 and solder.
Check that none of the link wires are touching each other on the top surface and that there are no solder splashes across adjacent tracks. Trim excess wire from the links using wire cutters.
close-up of track break
at A22 and soldered
switch S1 and
close-up of track surface
showing four track breaks
and soldered socket
This construction uses an integrated circuit known as a 555 timer which comes in a plastic package with 8 pins. The way these pins are connected determines how the 555 operates. The rate of switching on and off the light-emitting diode D1 is controlled by capacitor C1 and resistors R2, R3 and VR1. VR1 is a variable resistor which can be adjusted using a small screwdriver (not supplied in this kit).
Resistor R1 is connected to l.e.d. D1 to reduce the amount of current flowing through it. Too much current can cause an l.e.d. to burn out.
This project requires one PP3 battery (not supplied in this kit). In a test of this circuit, a Duracell Plus Power battery was still producing a good output of light after 40 hours of continuous use.
To construct this project you will need to use the following tools (not supplied):
Assembly Instructions for Project 11: Adjustable Flashing L.E.D. Using An Integrated Circuit
Please refer to the wiring diagram and read through these instructions very carefully before starting assembly.
PROJECT 11: ADJUSTABLE FLASHING L.E.D. USING AN INTEGRATED CIRCUIT
close-up of top surface
showing D1, R1, C1 and
position of i.c. socket
Push the negative lead through B6 and the positive lead through C6. Spread the ends of the leads of C1 slightly apart and carefully solder. Trim excess wire from the leads of C1.
4. The integrated circuit socket has 8 pins and its correct positioning on the track board is crucial. Position this socket so that the top left pin (pin 1) fits through hole B11. After pushing the socket pins through all eight holes, bend the pins slightly so that the socket does not fall off when the board is turned upside down. The pictures below show this stage of construction:
7. Push terminal pins from the track surface through to the top surface in positions A25, I25, A21 and A23. Terminal pins are a tight fit and pliers are usually needed to squeeze them through the holes. (Terminal pins have a habit of jumping off the table and are never found again - two spare terminal pins are provided in the kit.)
8. Make a track break position A22 and then solder the four terminal pins to the track surface. The pictures below show the track break and terminal pins on track A before and after soldering:
Think SAFETY. Act SAFELY.
You're important . . . so also read through the safety guidance sheet provided with the kit.
5. The copper tracks between the pins of the integrated circuit socket need to be broken so that pins on the same horizontal row are not connected. If the track was not broken between pin 1 and pin 8, for example, then a hazardous short‑circuit would occur when the battery was connected. Current would flow from the positive of the battery, along the copper track between pin 8 and pin 1 and back to the negative of the battery.
It is much easier to break the copper tracks at B12, C12, D12 and E12 before attempting to solder the i.c. socket into place. A copper track can be broken by carefully scraping the copper away with a sharp craft knife or, more easily, by pressing a 3 mm drill (not supplied in this kit) into a hole on the track surface and gently twisting the drill until all of the copper track at that position has been removed.
After the four breaks in the copper tracks have been made, carefully solder the socket pins to the track surface. Do not allow solder to splash across adjacent pins. The picture below shows the soldered i.c. socket and track breaks:
close-up of track break
at A22 and terminal pins
example of a
link wire staple
Twist the free ends of the cables attached to S1 around the terminal pins at A21 and A23 and solder them together. Make sure that a stray wire or excess solder does not bridge the gap between the two terminal pins.
14. Twist the red lead from the battery clip around the terminal pin in position A25 and solder them together. Twist the black lead from the battery clip around the terminal pin in position I25 and solder them together.
15. It is essential that the integrated circuit is correctly positioned in its socket. Identify pin 1 of the integrated circuit by the notch on the surface and the recessed dot:
9. Identify resistor R2 with bands of brown, black and red. Since space is limited on the track board, R2 will be positioned vertically rather than lying flat on the board. Push one lead of R2 through C17 and, using pliers, bend the other lead to fit though A17. Spread the ends of the leads of R2 slightly apart and carefully solder. Trim excess wire from the leads of R2 using wire cutters.
10. Resistor R3 has bands of brown, black and yellow. Bend the leads of R3 so that they can be pushed through holes C19 and H19. Spread the ends of the leads of R3 slightly apart and carefully solder. Trim excess wire from the leads of R3.
11. Variable resistor VR1 has 3 pins. Position VR1 so that the top, single pin fits through hole D22 and the other two pins fit through holes H21 and H23. After pushing through the holes, bend the pins slightly so that the variable resistor does not fall off when the board is turned upside down. Make a track break at position H22 between the two pins and then solder the pins of VR1 to the track surface.
12. Make a track break at position H17 to isolate R3 and VR1 from the left‑hand side of the circuit. (Check - there should now be a total of 7 track breaks on the track surface.)
13. Identify the two cables for the slide switch, S1. Push the end of one of the cables through the hole in the central tag of the switch, gently twist together and solder. Push the end of the second cable through the hole of either one of the remaining tags, twist and solder. Make sure that solder does not bridge the gap between these two connections on the switch. (The third tag on the switch is left unconnected.) Your switch should now look like that shown in the picture below:
Gently push the integrated circuit into its socket. It is often necessary to bend the pins slightly on the integrated circuit to ensure a good fit.
16. Assembly is now complete. Carefully compare your circuit with the wiring diagram and the pictures above. Check, again, that there are no solder splashes across adjacent tracks and that the tracks are completely broken in the correct positions.
Connect a new PP3 9 volt battery to the battery clip and switch on. Adjust the rate of flashing by turning a small screwdriver (or bent paper clip) in the slot of VR1 to alter its resistance.
1. Identify the positive and negative leads of the light-emitting diode, D1. A light-emitting diode will not work if it is connected the wrong way around and so correct identification of the leads is important! Push the positive lead of the l.e.d. through hole H2 and the negative lead through hole I2. Spread the ends of the leads slightly apart and carefully solder. Avoid solder splashing across the copper tracks where you have soldered the l.e.d. Trim excess wire from the leads of the l.e.d. using wire cutters.
2. Identify resistor R1 which has bands of yellow, violet and brown. It does not matter which way around a resistor is connected in a circuit. Bend the leads of R1 so that they can be pushed through holes D5 and H5. Spread the ends of the leads slightly apart and carefully solder. Trim excess wire from the leads of R1.
3. Identify capacitor C1. This type of capacitor has a positive lead and a negative lead. The negative lead is marked with a minus sign on the side of the canister as shown:
negative lead of a capacitor
marked with a minus sign
close-up of track surface
showing soldered joints
and i.c. socket before
track breaks made
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