The star is about 35cm across and designed to be displayed indoors in a window.
I originally created the star three years ago using a 16F872 controller. The original version worked ok - but had no spare memory for adding more features.
This new version uses a 18F2620 because I now prefer the 18F series and decided it would be a good general purpose 28 pin chip to use. It has more than enough memory (64K) so I can add as many features as I want now.
(It should also work using a PIC18F2525 instead if you find it easier or cheaper to obtain)
Since, I made the first version, brighter LEDs are now available and cost is much lower - this project currently uses a total of 60 comprising of 25 Blue, 15 Green and 20 Red.
Features An ever changing animated display, Patterns and speed chosen at random.
It can fade from one pattern to the next
Low power consumption
Currently 32 different patterns have been coded - and plenty of space available for more.
Circuit Description The circuit has been kept as simple as possible. The microcontroller uses portB to control the matrix columns through a cheap ULN2803 octal darlington transistor array.
This has the advantage of being compact,designed to work with logic levels without extra components and each output can carry 500mA, easily enough for this project.
The matrix rows are driven by portA directly and series resistors are used to limit the current supplied to each LED. Each port pin can only supply 25mA, with the multiplexing the effective current is even lower - but still bright enough.
PortC is eventually going to be used for a serial data link to control other stars, enabling the pushbuttons to make configuration changes etc. and three pins will control a colour changing effect to go in the centre of the star.
The microcontroller is clocked at 32Mhz using it's internal oscillator to save port pins - a timer function has been added, it is not very precise,but it can be adjusted to be good enough for use over the Christmas period though.
Operation On power-up, it lights all of the leds for several seconds as a diagnostic feature. Then it chooses patterns at random, also choosing a random speed for animating each pattern plus a random number of repeats for some patterns. Some patterns are enhanced by fading the leds - others are more appealing with no fade.
Settings options
The star works ok without any settings, although some features can now be set-up using the two pushbuttons.
Configuring the centre RGB led.
If you have used an RGB led with a common cathode (negative) lead, then it will work ok.
If you want to use an RGB led instead with a common ANODE (positive) lead, then you must connect the anode lead to +5V instead of 0V and enable it by holding the UP button pressed while applying power (this setting will then be retained in eeprom memory).
Enabling the timer function
(All settings are best made by viewing the star from behind)
This allows the star to turn-off at a chosen time. First, set the current time by pressing the SET button. The hours (12 hour time) are shown in a line of 12 leds across the star and the led at the top point lights for PM.
Press the UP button to step up the hours. Then press the SET button again to show Tens of minutes on the five blue leds in the middle of the star and Ones of minutes on the nine leds at the base of the star.
Press the UP button to count-up the minutes.
Press the SET button again when you have finished setting the time.
Setting the ON time
Hold the SET button pressed for several seconds until the centre RGB led lights RED.
Now set the ON time (just like setting the time as before) When done, press the set button and the centre RGB led will light GREEN for setting the OFF time.
Set the OFF time as before.
Press the set button again and the RGB led will light BLUE for adjusting the clock timing.
The clock speed is at default to begin with (shown by a single led at the middle-base of the star.
Pressing the UP button lights leds to the right to increase the speed and then to the left to decrease the speed.
The clock oscillator is factory preset to an accuracy of about 1 or 2% and this option allows it to be adjusted up or down in steps of 0.4%.
Press the set button again to end all settings.
The on/off times and speed adjustments are now stored in eeprom memory.
Resetting back to defaults
If you ever need to reset the chip back to defaults (removing saved timer and rgb led settings) it can be done by holding both SET and UP buttons pressed while applying power.
Toggling the display on/off
Press the UP button to to toggle the display off/on without using the timer function.
Several Stars can sync together.
To sync two or more stars together you just need a pair of wires.
You choose one star to be the Master and connect a wire from it's TX terminal to the RX terminal of one or more other stars. Then also link the Ground wires (0V)
For the possibility of longer distance links, I have used a slow speed serial data (2400bps) "Manchester" encoded protocol.
This may make it possible to link stars using short range RF data modules (Although I have not tested it because I don't have any!)
When using the serial link, the option to turn on/off the star's leds at preset times is controlled by the master star. (no need to configure it on any other Stars)
Files/Firmware You will need a PIC programmer compatible with the PIC18F2620 microcontroller.
If you don't have one - there are various articles on the web for constructing a simple serial port "JDM" type programmer. Good Freeware programmer software is easily available - such as "IC-Prog" or "WinPic800".
I shall update the file version here as features are added/bugs fixed etc.
PCB Layout The circuit is simple enough to construct on stripboard, Or use the single sided pcb layout design provided.
The microcontroller should be fitted in a socket. Connections to the pcb can be made either directly or use rows of connector pins. Power can be provided by a 9V DC wall-wart adapter rated at 300mA or better.
Star construction Drawing a five pointed star accurately can be time consuming - so I have made some templates to print-out and transfer to plastic sheet.
Making the star and wiring-up all the LEDs does take the most time, you need to be patient, it is very easy to make mistakes when doing the wiring.
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