Nuts and Volts - September 2015

September 2015 35

Scary Lane Haunt

( ScaryLane.com) started out as a simple home Halloween display over a decade ago. It wasn’t long before it was the must-see attraction for the

Listing 1.

Whittier community in

;The following lines of code are used to initialize the I/O lines
;going to the MSGEQ7 chip.  Use at the start of the program...
 High MSGEQ7Strobe ;initialization output to the MSGEQ7
 Low  MSGEQ7Reset

Southern California.

About six years ago, we added a two-story Ghost

;This subroutine is used to reads the 400HZ, 1000 HZ and 6.25 KHZ bands
;and opens or closes the jaw based on that band's output level.

Town façade that hides the house and has plenty of places for audio-animatronics, skeletons, props, and set dressing. The key to making this haunt great has been the use of electronics to run the show.

ReadEQU:
 pulsout MSGEQ7Reset,1;strobe the reset pin for 10ms
 pauseus 8 ;wait 80us for reset to end
 
 gosub SkipBand ;skip 63 hz band
 gosub SkipBand ;skip 160 hz band

Using more than a dozen custom-designed show and prop controllers, the Ghost Town literally comes alive on its own to entertain the neighborhood. The controllers time the fog machines, the lighting, and other effects based on the time and the weather conditions. Even the audio-animatronics changes based on the time of day or if it’s the big night of Halloween.

gosub GetBand ;get the 400 hz band
if Jaw_Temp>threshold then  ;higher than threshold voltage?
 High Jaw1motor;yes, then open jaw
else
 low Jaw1motor ;no, close Jaw
endif
 
gosub GetBand ;get the 1000 hz band
if Jaw_Temp>threshold then  ;higher than threshold voltage?
 High Jaw2motor;yes, then open jaw
else
 low Jaw2motor ;no, close Jaw

This year, I will be adding more sensors along the side walk so the show elements know where people are. Just imagine ... a person is walking by and the talking skeleton follows them. I will post the videos of the freaked out passers-by.

 gosub SkipBand ;skip 2,500 hz band
 gosub GetBand ;get the 6,250 hz band
 if Jaw_Temp>threshold then  ;higher than threshold voltage?
 High Jaw3motor;yes, then open jaw
 else
 low Jaw3motor ;no, close Jaw
 endif
return

The Interface

GetBand:
 low MSGEQ7Strobe ;Strobe line Low
 pauseus 4 ;wait 40.0 us till data is good
 readadc MSGEQ7Data,Jaw_Temp ;get the band's audio level
 High MSGEQ7Strobe ;Make Strobe line high
 pauseus 4 ;wait 40 us
 return ;now safe to strobe again.

The MSGEQ7 uses the reset and strobe inputs to control the multiplexer for spectrum band selection. Each time the strobe line is pulsed, the output will select the next band with the reset line starting a sequence back to the first spectrum band. This interface only needs two output lines and one analog input line, and is a piece of cake for just about any controller (like the Raspberry Pi, Arduino,

SkipBand:
 pulsout MSGEQ7Strobe,4 ;strobe line 40.0 us
 pauseus 4 ;wait another 40.0 us
 return ;now safe to strobe again.

The strobe timing diagram (Figure 7) shows how to use the reset and strobe lines to select the 63 Hz spectrum band and move along to the other six. To start reading the first spectrum band, the reset and strobe lines need to be set high. About 200 or more nanoseconds later, the strobe line should go low. Wait another 72 or more microseconds before changing the strobe line to read the analog input for the seven bands. When reading the bands, the chip responds to the high to low transition on the strobe line, but there is a short delay of 36 microseconds before the output is stable. The microcontroller can read the current level via the controller’s analog input line. Now, return the strobe line back to its high state and wait another 36 microseconds. Continue using the strobe line till all the bands have been read.