Nuts and Volts - November 2010

just as we did above. The day indicator is then decremented to point to the next candle. When all are lit, we can quit the repeat loop.

The last step is to wait for one more press — this time, to extinguish the candles. While I found a lot of good information regarding the lighting sequence of the Menorah, I never came across anything having to do with extinguishing the candles. This routine, then, will very slowly dim all at the same time:

repeat
until (getbutton(TRIG, 250) == true)

repeat level from 255 to 0
  repeat day from 8 to 0
 if (wicks[day] > 0)
 wicks[day] := level
  pause(24)

Note that we require a longer button press to extinguish the candles. This is by design to prevent an accidental bump of the button from extinguishing them too early. Note, too, that the loop timing for the fade-out is longer to create a nice, slow fade-out.

So, there you have it: a Propeller powered electronic Menorah. I think you'll find the code easy to modify and the candle simulation is far nicer than the old RC circuit. You can find the complete program in the downloads package as jm_pp12_menorah.spin.

THE KWANZAA KINARA

Before we move on, there is another, multi-day holiday celebration that uses a special candelabra: Kwanzaa. Those that celebrate Kwanzaa light the Kinara which has seven candles (one for each day). Since the Kinara candles are lit in ascending order each day, the code is a little simpler.

That said, I employed a little trick in this program to show you how to re-map outputs when they are not in the desired order. Let's say, for example, that we built a beautiful electronic Kinara and wired it with the outputs connected to each candle, moving left to right, in ascending order, like this:

1 2 3 4 5 6 7

The problem is that the Kinara candles are lit in this order:

2 4 6 1 7 5 3

In the event we can't (or don't want to) rewire the project, we can remap the outputs with a simple table in Spin. Here's a little table I created to remap the ( zero-indexed) day to the physical channel output on the board:

dat
kinara byte 3, 0, 6, 1, 5, 2, 4

On the first day (0), we will light the center candle (black) which is connected to P3. On the second day, we

SPIN ZONE

will light the outermost red candle which is connected to P0. The map should now make sense.

Here's the core code for the Kinara:

repeat
  repeat
  until (getbutton(TRIG, 100) == true)
  pause(250)
  if (getbutton(TRIG, 150) == false)
 if (day < 7)
 idx := kinara[day]
 repeat level from 0 to 255
 wicks[idx] := level
 pause(6)
 ++day
  else
 repeat level from 255 to 0
 repeat day from 6 to 0
 if (wicks[day] > 0)
 wicks[day] := level
 pause(24)
 quit

At the top, we have a little trickery concerning the button input. Since the Kinara candles are lit in ascending order and always start with the central candle, the program doesn't know what day it is — we tell it with each new press. What we do, then, is scan the button, wait a bit, then check again (note these periods are slightly longer than before). The idea is that a short button press will light the next candle and a long button press will extinguish those that are lit.

You can see that we treat the dat table like a simple array, reading the correct output for the day that we're presently lighting. Easy, right? I think so — and, it’s definitely easier than rewiring a project.

See jm_pp12_kinara.spin for the complete, commented listing.

For those that are interested in building a fully functional Menorah or Kinara, I again encourage you to consult the October ‘ 10 issue as there are detailed instructions on building candles from LEDs and items that you can pick up at any hardware store.

PLAYING WITH PROTOCOLS

More and more of those home Christmas displays that I enjoy so much are coming under computer control. I think a good chunk of the credit goes to a nifty bit of freeware called Vixen which was developed and maintained by my friend, KC Oaks.

If you're new to this stuff and really want to dive into the fray, I suggest that you check out www.doityourselfchristmas.com. It's a very active set of forums with many knowledgeable, highly enthusiastic members.

One of the more popular protocols supported by Vixens and a favorite with many DIY Christmas lighting enthusiasts is called Renard, which was created by a gentleman named Phil Short. Most of the code on the 'net for the Renard protocol is PIC-based as that's what Phil uses, though I have seen an implementation done in SX/B.