Bicycle back Safety Light

Flashing 13 LED unit, 3V supply

Also suitable for jogger/walkers

 

Parts:

R1_____________10K   1/4W Resistor
R2,R9,R10_____100K   1/4W Resistors
R3-R8,R11-R16__10R   1/4W Resistors
R17___________150R   1/4W Resistor

C1______________1ВµF  63V Polyester Capacitor
C2_____________10nF  63V Polyester Capacitor
C3____________100ВµF  25V Electrolytic Capacitor

D1-D13_____Red LEDs  5mm. or bigger, high efficiency

IC1,IC2________7555  or TS555CN CMos Timer IC

SW1____________SPST  Slider Switch

B1_______________3V  Battery (2 AA 1.5V Cells in series)

Device purpose:

This circuit has been designed to provide a clearly visible light, formed by 13 high efficiency flashing LEDs arranged in a pseudo-rotating order. Due to low voltage, low drain battery operation and small size, the device is suitable for mounting on bicycles as a back light, or to put on by jogger/walkers.

Circuit operation:

IC1 is a CMos version of the 555 IC wired as an astable multivibrator generating a 50% duty-cycle square wave at approx. 4Hz frequency. At 3V supply, 555 output (pin 3) sinking current operation is far better than sourcing, then LED D1-D6 are connected to positive supply. In order to obtain an alternate flashing operation, a second 555 IC is provided, acting as a trigger plus inverter and driving LEDs D7-D12. D13 is permanently on.
The LEDs are arranged in a two series display as shown below, with a center LED permanently on. This arrangement and the alternate flashing of the two series of LEDs provide a pseudo-rotating appearance.

LED arrangement: 

Notes:

• Flashing frequency can be varied changing C1 value.
• High efficiency LEDs are essential.

Adjustable Strobe Light

This one uses a much more powerful "horse shoe" Xenon tube which produces more light. You can also control the flash rate up to about 20Hz. Do not look directly at the flash tube when this thing is on!

Schematic

PC Board Layout

Parts Placement

Parts

R1	250 Ohm 10 Watt Resistor
R2	500K Pot
R3	680K 1/4 Watt Resistor
D1,D2	1N4004 Silicon Diode
C1, C2	22 uF 350V Capacitor
C3	0.47uF 400 Volt Mylar Capacitor
T1	4KV Trigger Transformer (see "Notes")
L1	Flash Tube (see "Notes")
L2	Neon Bulb
Q1	106 SCR
F1	115V 1A Fuse
Misc	Case, Wire, Line Cord, Knob For R2

 

Notes

1. T1 and L1 are available from The Electronics Goldmine

2. This ciruits is NOT isolated from ground. Use caution when operating without a case. A case is required for normal operation. Do not touch any part of the circuit with the case open or not installed.

3. Most any diodes rated at greater then 250 volts at 1 amp can be used instead of the 1N4004's.

4. Do not operate this circuit at high flash rates for more than about 30 seconds or else C1 and C2 will overheat and explode.

5. There is no on/off switch in the schematic, but you can of course add one.

12VDC Fluorescent Lamp Driver

A number of people have been unable to find the transformer needed for the Black Light project, so I looked around to see if I could find a fluorescent lamp driver that does not require any special components. I finally found one in Electronics Now. Here it is. It uses a normal 120 to 6V stepdown transformer in reverse to step 12V to about 350V to drive a lamp without the need to warm the filaments.

Schematic

Parts:

Part	Total Qty.	Description	Substitutions
C1	1	100uf 25V Electrolytic Capacitor
C2,C3	2	0.01uf 25V Ceramic Disc Capacitor
C4	1	0.01uf 1KV Ceramic Disc Capacitor
R1	1	1K 1/4W Resistor
R2	1	2.7K 1/4W Resistor
Q1	1	IRF510 MOSFET
U1	1	TLC555 Timer IC
T1	1	6V 300mA Transformer
LAMP	1	4W Fluorescent Lamp
MISC	1	Board, Wire, Heatsink For Q1

Notes:

1. Q1 must be installed on a heat sink.

2. A 240V to 10V transformer will work better then the one in the parts list. The problem is that they are hard to find.

3. This circuit can give a nasty (but not too dangerous) shock. Be careful around the output leads.

Electronic Candle

ELECTRONIC CANDLE

INSTRUCTION SHEET

Price - Stock No 210

This  circuit  will  detect  light  falling  on  the  Light Dependent Resistor (LDR or CdS).  When light falls on the  LDR  the  arrangement  of  resistors  at  the  base  of  the transistor T1 gives a change of voltage.  This biases or turns  on  the  transistor  which  turns  on  T2,  allowing sufficient  current  to  flow  to light the globe.  The arrangement of the  resistors at the base of T1 is called a Potential Divider.  It is adjusted to suit ambient light conditions by the variable resistor VR1.  A typical use would be to set the project up in the refrigerator. The light will light up in another room if you have enough wire, or you  could put  a  buzzer  in  instead  of the light and catch whoever is raiding the refrigerator.

Check Your Kit

Schematic Diagram

PCB Layout

1. Check the P.C.Board for damage to the tracks in transit. Continuity of tracks is best checked with an OHMS setting on a multimeter, or with an Electronic Circuit Tester.
2. Turn the board copper tracks down and begin to mount the components in the locations shown on the Placement Sheet. The values of the Resistors are determined by the colour bands. The resistors  will  fit  this  Board  more  comfortably  if  they are mounted vertically to the Board.  The Trimpot will fit the holes and position  the legs correctly.  Remember that the resistance is varied between Centre and one outside leg.  The other outside leg is a passenger, but is soldered to improve firmness of the trimpot to the Board.
3. Both  Transistors are BC548 (or BC547) so they are interchangeable.  The drawing shows the way the flat on the body goes.
4. The LED is polarised.  The flat on the globe goes to  the  K  (neg) side.  It won't work the other way round.
5. If  a  buzzer  is being fitted, the polarity must be observed - Red  wire is Positive (A), Black is Negative (K).  A power diode, D2 - IN4002- is fitted  to  avoid  feedback  to  the circuit from the LED and mainly, the buzzer.
6. The  battery snap is connected, Red to Positive.  A slide switch is included for a power on/off switch.  One wire of the battery snap, usually   the red one, is cut and the switch soldered in series in the line.
7. The Light Dependent Resistor  is  soldered  across  the  two  tracks shown.
8. Soldering  can  be  done progressively as components are mounted if  you like.  Refer Soldering Technique.

 To test the Electronic Candle, connect a 9V battery and  switch  it on.   Shield the Light Dependent Resistor from the light source and adjust  the trimpot until the LED goes off (and the buzzer stops).  Expose the LDR  to light and the LED (and buzzer) will operate.  Differing  ambient  light  conditions  will  require adjustment to the trimpot.  If the light is very strong - say sunlight - you may have to replace the trimpot  with  one  of  much higher value, say 100K or 500k or perhaps 1M.

TROUBLESHOOTING

If the project doesn't operate the process of trouble-shooting will consist  of

• checking  each  component  for  correct value, polarity where applicable  (LED,  Diode  IN4002,  Transistors,  Buzzer).
• Inspect  all  soldering  and  resolder  any  suspect  joints,  and  watch for bridges of solder across tracks which will create short circuits.
• As a party interest piece you can adjust the trimpot so  that  when  you  shine  a  small  torch  at the LDR the LED will light.  If the LED is  located away from the torch with two insulated  leads,  say  in  the  next  room,  then  the  LED  will  light  up  "on  command",  provided  that the  "command" is loud enough for the guy in the next room with  the  torch  to hear and shine his torch on the LDR.  Or perhaps you could conceal the LDR under  a  cloth.  Shine the torch at the spot where the LDR is and the LED  will glow in another place across the room.  MAGIC!

TECHNICAL NOTES

• You will find it interesting to measure  the  different  resistance across  the legs of the LDR under varying light flux.  A Multimeter set to the OHMS modes will show the enormous changes  to  resistance  across  the  legs.   The Light Dependent Resistor is a Cadmium-di-sulphide Cell as used in photography for light meters and  self-adjusting  (automatic)  exposure cameras.
• The  Potential Divider consists of the arrangement of LDR1 on one side, VR1 on the other side and  the  tapping  point  between them.   The  Voltage  at  the  tapping  point  is  varied  by the proportion of the values of these two resistors, and the total of the Voltage - Tap to Positive rail  +  Tap  to  Negative  rail  =  the total supply Voltage (9V).  Both  the resistors are variable in this case so a balance can be established to suit a range of light conditions. When the Voltage at the Tap (the Base of Transistor 1) rises, the transistor will switch on.  This allows current to flow between C and E legs.  The E leg is connected to the Base of Transistor  2,  so  the voltage turns T2 on.  The output of T2 with this setup is very large so a fairly large device could be driven.  Transistors in this setup are called a Darlington Pair.  The GAIN of each  of these transistors is about 100, but with Darlington Configuration the  total  Gain would be 100 X 100.  This means that 1 milliamp at the Base of T1 would result in 10000 milliamps available at  C or  E  of  T2.  R1, R2, and R3 are protection metering resistors, and R4 meters the current to the LED to approx. 20 milliamps, the specified draw of LEDs.
• Notice that the polarity of the Diode D2 is the reverse to what you would expect, viz. the K band is to the Positive  (A) rail.   This diode prevents damage to the circuit components that can occur from feedback from buzzers,  relays,  or  other  output devices.
• Connect  a  Voltmeter  from the B leg of T1 to Negative rail.  Switch  the  Candle  on  and  slowly  increase  the  light  intensity  on  the  LDR (by turning it slowly towards the light).  Note the Voltage reading when the LED  just  lights.   This  will  give  the  Switching  Voltage  of  the  transistors.   Check your reading against a Data Table for this transistor (BC 547).
• Check also the different readings +ve rail/ tap and -ve rail / tap.  These will be different, but should add together  to give Cell Voltage (around 9 Volts).