Construction details
for the PCB version are presented in pictures below. The PCB can be built up to
drive either LED clusters or off-board relays but not both. There are
a number of build
options which require a choice to be made as to which parts are
installed and these are described with the accompanying text.
A full component list
and part numbers for Rapid Electronics is provided at the end of the
section.
PCB straight from the etch
process |
PCB after drilling. Note the
three holes for the DC power connector (top right) need to
be milled into slots. |
Solder the small components to
the board first. Fit the voltage regulator (IC3) so it
matches the profile on the overlay. You may need to bend its
centre pin out slightly to line up with the holes in the
PCB. |
Next install the medium sized
parts. |
C4 needs to be installed
with the negative lead the correct way round.
|
 
If you construct the circuit
to drive off-board relays, install wire links into positions
JP1 and R1 (circled red). Do not fit R1 or R2 or the
second row of 2 pin header plugs |
The external switch input can
use either a 2 way 5mm screw terminal (shown left) or a
skeleton phono socket [cinch connector] (shown right) depending on your
preference. |
For the LED cluster version
you will need to install R1 and R2. |
After installing R1 and R2 use
the off-cuts from their leads to make the wire links LK2 -
LK5 as shown. |
Assembled board for use with
LED clusters. The optional isolated switch input components
have not been fitted.
For the LED cluster version
DO NOT fit JP1 |
The IC's must be installed
with the small notch as shown.
Also note the black band on Diode D1 |
|
Underside of
the completed board. |
Completed
board with isolated switch input components installed.
Ensure D1 is located with the black band as shown.
The value of R6 needs to be chosen according to the voltage
used in the external input application. |
Switch Inputs
There are two
external switch inputs and an on-board switch. Any of the
switches can be used to operate the unit; you choose which one
depending on your specific requirements.
The
on-board switch is primarily for testing although it can be used
for normal operation if desired. All three switches are
connected to the controller in parallel therefore the use of any
one switch input does not preclude the use of the other two.
SW1 Switch
The SW1 switch on the
PCB can be used for testing the board without any external switches
connected.
The start sequence
is triggered on the release of the switch not the initial press.
Non isolated switch
input
The CN1/CN2
connector provides input for a non-isolated switch to be
connected to the controller.
Isolated switch
input option
The isolated
switch input needs its own power source to turn the LED on in
the opto-isolator. If you include the
isolated switch input option you need to select the value of R6
according to the voltage used in the external circuit.
Suggested values are
shown in the table below. Use a 5% 1/4watt carbon film resistor.
With the values shown the LED current will be approximately 30-35mA.
|
Voltage (DC) |
R6 |
| 3 |
47R |
| 5 |
100R |
| 6 |
150R |
| 7.5 |
180R |
| 9 |
220R |
| 12 |
330R |
Right. Testing the
board using the isolated switch option.
The red/black crocodile clips
are connected to a bench power supply.
The isolator will work with
various input voltages provided R6 is correctly specified (see table
above)
|
 |
LED Clusters
The LED clusters are
Kingbright type BL0307-50-44.
These contain 50 LED's connected as 10 parallel strings of 5 LEDs as
shown in the schematic below. Available from Rapid Online - Rapid Electronics Ltd.,
part No 56-2985
Download datasheet for
Kingbright LED
Cluster
Ensure they're connected to the
controller with the red and white leads as shown in both the photos
and indicated on the PCB overlay. The LED clusters
illuminate sequentially from 1 to 5 and this is indicated on the PCB
overlay.
The board will drive either a single
row of 5 LED clusters or two rows. When using it with two
rows, connect the second set of LED clusters to the second column of 2
pin headers (circled yellow) in the photo below.
Adjusting Brightness
When JP1 is open, the controller
drives the outputs using a PWM (pulse width modulated) signal.
This allows the brightness of the LEDs to be controlled by adjusting
the position of PR1. The PWM frequency is ~350Hz to avoid any
visible flickering.
The brightness control input is an
analogue signal varying from 0 volts (dim) to 5 volts (bright).
For the technically minded it is possible to modify the circuit to
use a Light Dependant Resistor to automatically adjust the LED
brightness to match the ambient lighting.
Drive modes
The software supports three drive
modes of which two are supported on the PCB. The third mode
may be used if you incorporate the microcontroller into your own
hardware design.
The design of the circuit uses a
single current limiting resistor (R1 & R2) for each row of LED
clusters. For this to work only one LED cluster can be on at any
time otherwise the more LEDs that turn on, the dimmer they get.
The software drives each output one at a time but it does so 350
times a second and through persistence of vision to the human eye
they appear to be on at the same time. The reason it has been
implemented this way is for two reasons.
-
The total maximum
current required is that of 2 LED clusters rather than 10 so a
smaller and cheaper power supply can be used.
-
The drive circuit
uses a single ULN2003A transistor array and two resistors which
keeps the cost down and the complexity of the circuit and PCB
layout are simplified.
|
Mode |
RA0 (JP1) |
RA4 |
|
|
Direct |
closed (Gnd) |
open |
Use with
relays and other devices that can't use PWM |
|
Direct PWM
* |
open |
closed (Gnd) |
Use with
LED driver that has individual current limiting |
|
Multiplexed PWM |
open |
open |
Use with
LED driver that has common current limiting |
The RA0 / RA4 inputs have internal
weak-pull enabled so there is no need for external pull up
resistors.
* On the PCB, RA0 is connected to JP1 but RA4 is not
made directly available since the Direct PWM mode isn't
supported by the hardware on the PCB.
Driving
Relays
If you use the PCB to drive relays
they should be rated for operation at 12V DC and the coil resistance
should be >150 ohms otherwise there is a risk of damage to IC2
(ULN2003A).
Connect each relay coil to the
2-pin header on the PCB. You'll need 5 relays in total,
one connected to each output.
Also ensure JP1 is closed
otherwise the relays will be driven with a PWM signal and won't
operate correctly.
In the UK all the components can be
obtained from Rapid Online - Rapid Electronics Ltd.. I've provided a component list with their part numbers and
descriptions. The parts used are all commonly available and should be
obtainable from most good electronic component distributors anywhere in
the world.
Note: where it says
(option)
in the description, you only need
the part if you are building it with the selected option.
| Schematic part |
Qty |
Description |
Rapid Part No |
| LED Clusters |
5(10) |
52MM ULTRABRIGHT LED CLUSTER
(RC) |
56-2985 |
| C1, C3 |
2 |
100N 2.5MM Y5V DIELEC.CERAMIC
(RC) |
08-0275 |
| C2 |
1 |
220N 5MM Y5V DIELEC.CERAMIC
(RC) |
08-0280 |
| C4 |
1 |
100UF 25V LOW
IMPEDANCE ELECTROLY CAP RC |
11-2922 |
| R1, R2 |
1 pack |
PACK 10 10R PR02
2W POWER
RESISTOR RC |
62-6708 |
| R3 |
1 pack |
PACK 100 3K3 0.25W CF RESISTOR
(RC) |
62-0382 |
| R4 |
1 pack |
PACK 100 100R 0.25W CF RESISTOR
(RC) |
62-0346 |
| R5 |
1 pack |
PACK 100 150R 0.25W CF RESISTOR
(RC) |
62-0350 |
| R6 |
1 |
See text
(option) |
- |
| PR1 |
1 |
6MM CERMET
POTENTIOMETE HIGH TEMP 10K (RC) |
67-0354 |
| PWR-ON LED |
1 |
MINIATURE 3MM PURE GREEN LED
(RC) |
55-0107 |
| D1 |
1 |
1N4148 75V 150MA
SIGNAL DIODE. (RC) (option) |
47-3308 |
| |
|
|
|
| IC1 |
1 |
PIC16F684-I/P MICROCONTROLLER (RC)
(Needs programming) |
73-3388 |
| IC2 |
1 |
ULN2003A
TRANSISTOR ARRAY 7 MATCHED (RC) |
82-0618 |
| IC3 |
1 |
DA78L05 V REG +5V
100mA TO-92 TRU (RC) |
47-3612 |
| IC4 |
1 |
CNY17-3 TRANSISTOR
OPTOISOLATOR (RC) (option) |
58-0886 |
| LED cluster plug |
10 |
2 WAY SINGLE ROW PCB HEADER
PLUG (RC) |
22-0520 |
| |
|
|
|
| Socket for IC1 |
1 |
14 PIN 0.3IN DIL
SOCKET (RC) |
22-0155 |
| Socket for IC2 |
1 |
16 PIN 0.3IN DIL
SOCKET (RC) |
22-0160 |
| Socket for IC4 |
1 |
6 PIN LOW
PROFILE IC SOCKET (RC)
(option) |
22-0145 |
| SW1 |
1 |
5.85MM RIGHT ANGLE
TACT SWITCH (RC) |
78-1154 |
| PSU |
1 |
15W MINIPLUG TOP SM PSU 12V
DC 1.2A (RC) |
85-2902 |
| DC Power Skt (J1) |
1 |
2.1MM PCB DC POWER
SOCKET
(RC) |
20-0970 |
| CN1 |
1 |
BLACK PCB SKELETON
PHONO SKT (RC) (option) |
22-1122 |
| CN2 / CN3 |
1 |
2 WAY 16A
PCB TERMINAL BLOCK (RC) (option) |
21-0112 |
The PIC 16F684 microcontroller needs
programming before use. Source code and programmer ready HEX files
can be downloaded here.
Download:
Firmware version 1.0.6, release
date 23/05/2008
Not got a programmer? Buy
a pre-programmed PIC from the
On-line store
