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Assembly and Operating Instructions for Kits


Assembly Instructions for Sound Trigger on a Breadboard (legacy SK2-BB)


Note: These instructions are for kits before v10.


Assembly instructions


These instructions may be used in combination with the instructions for building a delay unit in order to provide a sensitive sound trigger with a selectable delay.  For instructions on building the delay unit, go here.


Parts List


The following parts are included with the kit. (If you purchased the SK2 in combination with a delay unit, then a single set of wires was provided with the combination.)


400-V SCR (EC103D)
2N2222 transistor (or PN2222A)
Piezoelectric element


1 5.1-kΩ (green-brown-red)
1 68-kΩ (
1-kΩ potentiometer (yellow knob)

3-ft of 2-conductor cable
Hookup wire
9-V battery cab


*A fresh 9-V battery is required but not included with the kit.  You'll also need a wire cutting and stripping tool such as the one shown to the right.
Click for larger view


Click on the thumbnails below in order to view full-size images of the breadboard with the components that have been added in each step.


Using the Breadboard


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The breadboard offers an easy way to build electrical circuits without soldering. The 2"x3" breadboard provided with your kit contains an array of holes where wires and components are to be inserted. The holes in the center portion of the breadboard are identifiable by row (vertical in the photos) and column (horizontal).  There are two sets of 30 rows numbered by 5's, and each set of rows has 5 columns labeled a-e and f-j. The 5 holes on each row are electrically connected to each other (but not across the center channel), so any components inserted into the same row would be connected just as if they had been soldered.  However, the components can be removed and replaced with other components at any time, without the hassle of unsoldering and resoldering parts.


On either side of the breadboard are two columns marked by blue and red lines. The 25 holes in each column are electrically connected, but the columns aren't electrically connected to each other.  The outermost column marked with the red line at the top will be used for all +9 V connections, while the outermost column marked with the blue line at the bottom will used for all ground (negative) connections.



Assembling the Sound Trigger


Note that the photographs show a delay unit already built on the right side of the board.  The sound trigger may be used with or without the delay unit. However, the 9-V battery cable is required for the operation of either kit.  This is the cable coming in from the left with the red and black leads above and below the piezoelectric element.  The column of 25 holes to which the red wire is connected will be termed the positive column, while the column to which the black wire is connected will be termed the negative column.  While wiring the circuit, be sure to have the battery disconnected from the battery cable.
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Step 1: Adding the Piezoelectric Element


The piezoelectric element has two pins and is the sound detecting component of the circuit.  The polarity of the pins is indicated on its casing by a (+) for the positive pin and a (-) for the negative pin.*  Place the positive pin into Row 4, Column c, and the negative pin into Column g of the same row.


*A newer version of the piezoelectric element has a black case and red and black wires.  The red wire goes into Row 4, Column c, and the black wire goes into Column g of the same row.

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Step 2: Adding the Potentiometer


The 1-kΩ potentiometer (yellow) allows you to adjust the sensitivity of your sound trigger.  It has three legs, two in the front and one in the rear. Place the two front legs over Rows 11 and 13 on Column i, and the rear leg over the nearest hole on the column directly adjacent to the positive column. (This column should be marked by a blue line, and will only be used for connection to the potentiometer.)  The front legs should be facing the center of the breadboard, while the rear leg faces the outside of the breadboard. Press the legs in firmly as far as they will go, but avoid bending them.

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Step 3: Adding the SCR and Transistor


The silicon-controlled rectifier (labeled EC103-D) is the output of the sound trigger circuit.  Hold the SCR as in the diagram to the right in order to identify the leads.  Putting in this SCR is easy since all three leads go in consecutive rows along Column g. Put the cathode into Row 14 on Column g. The gate will then go into Row 15, and the anode into Row 16 of that column.

SCR pin diagram

A = anode (+)
G = gate
C = cathode (-)

The transistor looks identical to the SCR but is labeled PN2222A (or 2N2222A). Its three leads go in consecutive rows along Column c.  To identify the leads of the transistor, hold it as in the diagram to the right.  Put the emitter into Row 10 on Column c.  The gate will then go into Row 11, and the collector into Row 12 of that column.

Transistor pin diagram

E = emitter (-)
B = base
C = collector (+)

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Step 4: Adding the Resistors


Locate the blue-gray-orange resistor (68 kΩ).  Insert one end into Row 11, Column e, and the other end into Column g of the same row.  Next, find the green-brown-red (5.1 kΩ) resistor.  Insert one end into Row 11, Column h. The other end should reach over to the nearest hole in the positive column.


You may wish to trim the leads of the resistors so that they sit closer to the breadboard.  This will reduce the chance that the leads of two components accidentally touch each other and create a short.

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Step 5: Adding the Wires


Now connect all your electronic components together. Each wire only needs to be 2 inches in length or less. You can estimate how much you'll need to bridge across two holes before cutting, although it's always better to have longer wires than ones that are too short.


Strip about 1/4" of insulation off each end. The list below will tell you which rows and columns your wire ends should fit into. The longest wires are listed first so if you happen to cut a piece that's too short, you'll be able to use it later.


Longest wires (~1.5 inches)

Smallest wires (~1 inch or less)

End 1  End 2 End 1  End 2
Row 14, Column f  negative  Row 10, Column a negative
Row 11, Column d  Row 4, Column j  Row 4, Column a negative
Row 12, Column e  Row 15, Column h  Row 15, Column i blue-lined column adjacent to positive column

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Step 6: Connecting the Sound Trigger to a Delay Unit


If you're using the sound trigger without a delay unit, then skip to Step 7a.  Otherwise, add a wire from hole 16h, the output of the sound trigger, to 18h, the input of the delay unit. Then skip to Step 7b.

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Step 7a: Connecting a Flash Unit to the Sound Trigger Output


The 3 feet of 2-conductor cable may be used to connect the output of the sound trigger to the PC cord of a flash unit. You’ll need to provide your own PC cord.


From one end of the 2-conductor cable, strip 1" of the gray insulation, being careful not to cut the insulation on the red and black wires.  Then strip 1/2" of insulation from each of the red and black wires.  These will connect to the breadboard.  Next, strip 2" of the gray insulation from the other end of the cable.  Strip each of the individual wires back 1".  These will connect to the PC cord.  One way to make this connection is to cut the socket off the end of the PC cable, strip the insulation on the individual PC wires back by 1", splice the red wire of the gray cable to the positive wire of the PC cable, and splice the black wire of the gray cable to the negative wire of the PC cord.  (The positive wire of the PC cord is usually the wire that goes to the center pin of the PC socket.)  For more information on connecting to a PC cord, see this page:


Insert the end of the red wire on your ½" end into Row 16, Column i, and the end of the black wire into Row 14, column i.

Skip to Step 8.

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Step 7b:  Connecting a Flash Unit to a Delay Unit Output


Having constructed a delay unit, you'll already have an output cable for your flash prepared.


For the delayed output (Output 2) of the delay circuit, connect the red wire to Row 18, Column b and the black wire to the negative column. (This is the connection shown in the photograph.)


For the undelayed output (Output 1) of the delay circuit, connect the red wire to Row 16, Column b and the black wire to the negative column.


Step 8: Operating the Circuit


With a 9-V battery connected to the battery clip and your flash unit connected to the PC cord, you can now test your circuit.  Clap your hands about three feet from the piezoelectric element.  The flash unit should discharge.  It may be delayed slightly if you're connecting to Output 2 of the delay unit. If you don't get a discharge, one possible reason is that the sensitivity isn't adjusted correctly.


Adjusting the sensitivity of the sound trigger: Turn the potentiometer (yellow knob) in one direction or the other until the flash discharges spontaneously. Then back up the dial just before the point of spontaneous discharge.


Another way to adjust your trigger’s sensitivity is to vary the distance between the circuit and your sound source.  The closer your circuit is to the source, the more intense the sound will be when it arrives at the piezoelectric element.  Move the circuit closer for fainter sounds and farther away for louder sounds.




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