Kitronik Timed Night Light Kit User manual

TIMED NIGHT LIGHT KIT
RELAX YOUR WAY TO SLEEP WITH THIS
ES
S
ENTIAL INFORMATION
BUILD INSTRUCTIONS
CHECKING YOUR PCB & FAULT-
FINDING
MECHANICAL DETAILS
HOW THE KIT
WORKS
Version 2.0

Timed Night Light Essentials
www.kitronik.co.uk/2139
Build Instructions
Before you start, take a look at the Printed Circuit Board (PCB). The components go in the side with the writing on
and the solder goes on the side with the tracks and silver pads.
Start with the five resistors:
The text on the PCB shows where R1, R2 etc go.
Ensure that you put the resistors in the right place.
PCB Ref
Value
Colour Bands
R1 & R7
10K
Brown, black, orange
R4 & R8
1M
Brown, black, green
R5
47

Yellow, purple, black
The LDR needs to be soldered into the board where it is marked R3.
Solder the variable resistors into R2 & R6. They will only fit in the holes in the board when
they are the correct way around. The two resistors are different values, R2 is a 220K and R6
is 10M, make sure that you put both in the right place.
The four FETs should be placed into Q1 to Q4. All four are the same type but it is important that
they are inserted in the correct orientation. Ensure that the shape of the device matches the
outline printed on the PCB. Once you are happy, solder the devices into place.
Solder the Light Emitting Diode (LED) into LED1. The LED won’t work if it doesn’t go in the right
way around. If you look carefully one side of the LED has a flat edge, which must line up with the
flat edge on the lines on the PCB.
Solder the capacitor into the board where it is marked C1. It is important that the ‘-’ on the capacitor
matches the ‘----’ markings on the PCB.
SOLDER THE LDR
2
PLACE RESISTORS
1
SOLDER THE VARIABLE RESISTORS
3
PLACE THE FETs
4
SOLDER THE LED
5
SOLDER THE CAPACITOR
6

Timed Night Light Essentials
www.kitronik.co.uk/2139
Now you must attach the battery clip. It needs to be connected to the terminals marked ‘Power’.
The red lead should be soldered to the ‘+’ terminal also marked ‘red’ and the black lead should be
soldered to the ‘-’ terminal also marked ‘black’. Connect the PP3 snap on to the 3xAA battery box.
Do not use a 9V battery with this circuit.
Checking Your Circuit
Check the following before you connect power to the board:
Check the bottom of the board to ensure that:
All the leads are soldered.
Pins next to each other are not soldered together.
Check the top of the board to ensure that:
The body of the four FETs matches the outline on the PCB.
The flat edge on the LED lines matches the outline on the PCB.
The red wire on the power clip goes to the connection marked ‘red’ and the black wire to the connection marked
‘black’.
R1 & R7 are 10K resistors (brown, black, orange colour bands).
R5 is a 47 resistor (yellow, purple, black colour bands).
R2 has 220K printed on the side.
Testing the PCB
Set the duration to min – fully anti-clockwise.
Set the light level so that it points at the other trimmer.
Power the board up and cover the LDR – the LED should turn on for about five seconds. Uncover the LDR, then cover
it again, the LED should turn on again for about five seconds. The duration and light level can be adjusted.
If the circuit doesn’t function as expected, use the fault finding flow chart to locate the problem.
ATTACH THE BATTERY CONNECTOR
7

Timed Night Light Essentials
www.kitronik.co.uk/2139
Fault Finding
Is the
LED off?
No
Yes
Yes
Even if dimly
Check
• The batteries are good and in the right way around.
• Check the power clip is connected the right way
around and soldered correctly.
• The LED is the right way around, for a short or dry
joint.
• Q1 is the right way around, for shorts or dry joints.
• Q2 for shorts or dry joints.
• Q3 is the right way around or for shorts.
• Q4 for shorts or dry joints.
• R3 for a short or dry joint.
• R1, R2, R5 & R8 for dry joints.
• R5 is a 47 resistor (yellow, purple, black).
• R1 is a 10K resistor (brown, black, orange).
• C1 for a short.
Fault finding
flow chart
Start
Set the two trimmers as
shown in the diagram.
Then power the board up
Can you
adjust the light
level & duration
OK?
Stop
No
No
After about
5 seconds does
it go off?
Yes
NoYes
The LED is constantly on
All 3 pins on Q2 are shorted.
The LED is on dim & goes brighter when the LDR is
covered
Check Q2 & Q3 for shorts.
Check
• Q2 is the right way around.
• Q3 for dry joints.
• Q4 is the right way around and for shorts.
• R6 for dry joints.
• R7 for dry joints.
• R7 is a 10K resistor (brown, black, orange).
Check
• Q2 for dry joints.
• R5 is in the right
place, 47
resistor (yellow,
purple, black).
• C1 for dry joints.
The LED
flashes briefly
If the setting of the light level is close to min & the
maximum duration is about a minute
The two trimmer pots are in the wrong place.
(R2 should be the 220K)
D
DuurraattiioonnLLiigghhtt lleevveell
Cover the LDR
(and keep it covered)
Does the
LED light?
Is the
LED off?
No
Yes
Yes
Even if dimly
Check
• The batteries are good and in the right way around.
• Check the power clip is connected the right way
around and soldered correctly.
• The LED is the right way around, for a short or dry
joint.
• Q1 is the right way around, for shorts or dry joints.
• Q2 for shorts or dry joints.
• Q3 is the right way around or for shorts.
• Q4 for shorts or dry joints.
• R3 for a short or dry joint.
• R1, R2, R5 & R8 for dry joints.
• R5 is a 47 resistor (yellow, purple, black).
• R1 is a 10K resistor (brown, black, orange).
• C1 for a short.
Fault finding
flow chart
Start
Set the two trimmers as
shown in the diagram.
Then power the board up
Can you
adjust the light
level & duration
OK?
Stop
No
No
After about
5 seconds does
it go off?
Yes
NoYes
The LED is constantly on
All 3 pins on Q2 are shorted.
The LED is on dim & goes brighter when the LDR is
covered
Check Q2 & Q3 for shorts.
Check
• Q2 is the right way around.
• Q3 for dry joints.
• Q4 is the right way around and for shorts.
• R6 for dry joints.
• R7 for dry joints.
• R7 is a 10K resistor (brown, black, orange).
Check
• Q2 for dry joints.
• R5 is in the right
place, 47
resistor (yellow,
purple, black).
• C1 for dry joints.
The LED
flashes briefly
If the setting of the light level is close to min & the
maximum duration is about a minute
The two trimmer pots are in the wrong place.
(R2 should be the 220K)
DDuurraattiioonnLLiigghhtt lleevveellDDuurraattiioonnLLiigghhtt lleevveell
Cover the LDR
(and keep it covered)
Does the
LED light?

Timed Night Light Essentials
www.kitronik.co.uk/2139
Designing the Enclosure
When you design the enclosure, you will need to consider:
The size of the PCB (below left).
How big the batteries are (below right).
These technical drawings of the PCB and battery holder should help you to plan this.
All dimensions in mm.
Four PCB mounting holes are 3.3 mm in diameter.
Mounting the PCB to the
enclosure
The drawing to the left
shows how a hex spacer
can be used with two
bolts to fix the PCB to the
enclosure.
Your PCB has four
mounting holes designed
to take M3 bolts.
47
57
25
29
8
63.5

Timed Night Light Essentials
www.kitronik.co.uk/2139
How the Timed Night Light Circuit Works
When the Light Dependant Resistor, or LDR for short, (R3) is in day light, the resistance will be low. R1, R2 & R3 are
connected together to form a potential divider, where R2 sets the amount of light needed to switch the FET. With
the LDR having a low resistance, the voltage on the gate of the FET Q1 will be low and the FET will be off. In this case
the two FETs Q3 and Q4, which drive the LED, don’t have a 0V connection and as a result the LED won’t light. Also
whilst Q1 is off, the resistor R4 pulls the gate of FET Q2 into a high state and, as a result, current flows through the
drain source of Q2 and charges capacitor C1 through R5.
When the LDR (R3) is dark the resistance is much higher and, consequently, the voltage on the gate of the FET Q1 is
high and the FET is turned on. In this case the FETs Q3 and Q4 now have a 0V connection and the LED can operate.
Initially the capacitor C1 is charged and, as a result, has 5V across it. This means that the gate of FET Q3 is low, and
therefore the FET is turned off. As a result, the gate of Q4 is held in a high state by resistor R8 and the LED is turned
on. Over time the Capacitor (C1) is discharged through R6 & R7 and, gradually, the voltage across it drops. As the
capacitor voltage reduces, the voltage on the gate of Q3 starts to rise. After a period of time there will be sufficient
voltage on the gate of FET Q3 and the FET will turn on. When this happens the gate of FET Q4 will be pulled low and
the FET Q4 will switch off, as will the LED.
Resistors R1 & R7 are present so that the circuit can’t be damaged if the trimmer potentiometers are set to zero.
R1
R2
R3
R4
R6
R5
R7 R8
Q1
Q3 Q4
Q2
C1
LED1
0v
5v
R1
R2
R3
R4
R6
R5
R7 R8
Q1
Q3 Q4
Q2
C1
LED1
0v
5v

Online Information
Two sets of information can be downloaded from the product page where the kit can also be reordered from. The
‘Essential Information’ contains all of the information that you need to get started with the kit and the ‘Teaching
Resources’ contains more information on soldering, components used in the kit, educational schemes of work and so
on and also includes the essentials. Download from:
www.kitronik.co.uk/2139
Every effort has been made to ensure that these notes are correct, however Kitronik accept no responsibility for
issues arising from errors / omissions in the notes.
Kitronik Ltd - Any unauthorised copying / duplication of this booklet or part thereof for purposes except for use
with Kitronik project kits is not allowed without Kitronik’s prior consent.
This kit is designed and
manufactured in the UK by Kitronik