Interested in building an artificial fire for your haunt? Perhaps you would like a big cauldron suspended over a bed of glowing embers. You might be interested in the following story...

• Story
• Schematic

When the Samhain ceremony was over, most of the crowd left the central hall. I immediately started cleaning up, scurrying back and forth with various equipment. Soon, I noticed that one of the crowd had wandered back into the hall and was headed towards one of my props. He was particularly interested in the artificial fire that I had burning *1 in the middle of the room. He knelt down to examine it, and I felt a little upset, because I worked very hard on it and didn't want it damaged. Furthermore, it was my personal property. But he looked curious and not destructive, so I headed that way, but didn't interrupt him.

The visitor turned over the circular bed of embers and looked underneath. A bundle of wires terminated in a gray plastic plug, inserted into the side of a black plastic box. A small pack of penlight cells terminated in a black plug, also inserted into the black box. And that's all you could see. He stared at it for a while, decided that he couldn't learn anything from it, put it back into place, and left the room.

I was tempted to walk up behind and tell him exactly what was inside. Depending on his background, he would either be impressed by the ridiculous overkill, or completely clueless. I was tempted to say this:

It starts with a 4060 *2, with that nice double inverter input stage that makes it so easy to slap together an oscillator. I used a .01 ufd cap and a 50 K ohm trim pot. Then it dumps into a 14-stage binary ripple counter. Unfortunately, they don't bond out all the stages, lacking a couple of pins in the 16-pin DIP. The best you can do is seven bits of contiguous output count, and I feed that into the low order addresses of an 8Kx8 JEDEC byte-wide memory. The reset pin on the counter is disabled, so it runs forever, cycling through the 128 different cells that constitute an output "pattern". The remainder of the address is divided into two sets: the next four bits are driven from a hex encoded DIP rotary switch. This is used to select which pattern is to be displayed. The last two bits go to a DIP switch, and are used to select amongst four different sets of patterns, with all permutations of normal vs inverted and forward vs backwards. The bytewide's ~CE and ~OE pins are strapped low, so the data presented at the output represents all eight bits of the current cell in the currently selected pattern with the currently selected modifications. Each output bit is run through a 100 ohm resistor into the base of a TIP 122 NPN power Darlington. The emitters are all bussed together, going to ground. Each collector goes to two small incandescent lamps in series. The free ends of each of the lamp chains are bussed together and fed from the lamp source. By the way, the four cells in the battery pack provide 6 volts for the logic, but is tapped at only 4.5 volts to run the lamps. I didn't want them too bright; it's just supposed to be a bed of embers. There is also a small signal diode in series with the power transistor base in order to prevent parasitic currents from lighting the lamps when the bytewide is outputting a zero. Hrumph. That's about everything except the programming. Instead of an EPROM, for the bytewide, I used a Dallas low power CMOS SRAM. Since it is internally battery backed, I can program it by sticking it in any bytewide RAM socket and merely writing to it. In this case, I used the SBC that I normally use for home control. While I was fiddling with the SBC as a bytewide writer, I discovered that the super capacitor memory backup that I installed some months ago works so well that it's scary, but that is another story. I wrote a program on the SBC in FORTH to generate the patterns and write all four permutations into the appropriate quadrants of the bytewide. At this time, I only have three of the sixteen patterns populated. The first is a single walking bit in a wrap-around ring. The second pattern is a single 1 bit sloshing back and forth. The third pattern is produced by generating two pseudo random numbers of three bits for each cell in the pattern. I then light the corresponding bits. This gives me one or two one bits per pattern cell. I'll write some more patterns later. In order to get the flicker, I selected the inverted version of the two random bits and cranked the clock rate up as high as it would go. I know that it is overkill for the flicker, but I have plans for some of the other patterns.

I was thinking of saying all of that to the inquisitive fellow at Samhain, but decided not to. And after recounting every detail of the black box to Erin, she agreed that she didn't understand a word of it. Yet.

- Dennis

*1 - Actually, the fire was set up as having burned down to a bed of glowing embers. It came complete with artificially charred portions of wood, done with a chisel, mallet, and black paint.

*2 - When I told this story to David Harmon, he chuckled when I mentioned the 4060. He immediately identified it as one of my favorite chips, despite the silly bond out.

Thank you for visiting. Your comments are welcome.
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