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Assembly and Operating Instructions for Kits


Instructions for Building the Multi-Trigger on a Breadboard (MT-BB, v10)


Assembly instructions for other kits


These instructions are for version 10 of the MT-BB kit.


Multi-Trigger Breadboard


Parts List


The following parts are included with the MT-BB kit.  For photos of the parts, see the Parts Guide.


If you prefer to work out your own design, see the circuit schematic.


Optoelectronic, semiconductors, and transducers


Piezoelectric element (black case)
Infrared emitter (blue case)
Infrared phototransistor (clear case)
PN2222A transistor

4 400-V SCRs (EC103D)
2 red LEDs
555 timer IC
556 timer IC


Caution: Ground yourself before handling the 555 and 556 timers. These parts can be damaged by static discharges.



4 of 100 Ω (brown-black-brown)
3 of 470 Ω (yellow-violet-brown)
2 of 100 kΩ (brown-black-yellow)
1 of 1 kΩ (brown-black-red)
1 of 5.1 kΩ (green-brown-red)
1 of 1 MΩ (brown-black-green)
2 of 22 kΩ (red-red-orange)


1-MΩ potentiometer (blue knob)
1-100 kΩ potentiometer (brown knob)
10-kΩ potentiometer (white knob)
1-kΩ potentiometer (yellow knob)



2 0.0047-µf (472 or 0047)
2 0.01-µf (103 or 103Z)
2 0.047-µf (473 or 047)
1 0.1-µf (104)


Electrolytic - cylindrical metal case
1 0.47-µf
1 10-µf

Wires and Cables

6-ft of 3–conductor cable

1-ft of 2-conductor cable
6 6” pieces of hookup wire
18” yellow wire (save this for the photogate cable)

2 breadboard pins
8” of heat shrink tubing

9-V battery cable (A fresh 9-V battery is required but not included with the kit.)



Tools needed (not included)


Wire stripper

15-30 W soldering iron, solder, wet sponge

Lighter or matches to shrink the heat-shrink tubing



Preparing the Microphone Cable
Piezo disc piezo disc deep
Version 1 Version 2

Note: In June of 2016, we started providing a new piezoelectric disc. Photos of the new and old discs are shown to the left. The new version 2 requires the addition of a cable. For this purpose, the following additional parts are included in the kit: 1-ft of 2-conductor cable, 3-in of heat-shrink tubing, 2 breadboard pins.


Prepare the cable first according to these instructions.



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 Circuit


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Step 1: Adding the Battery Cable and the Timer ICs



The 9-V battery clip is shown to the right. Insert the red wire in the hole on the far left of the upper red column and the black wire in the hole on the far left of the lower blue column. Don't connect the battery until the circuit construction is complete and you've double-checked all connection.


Caution: Ground yourself before handling the 555 and 556 timers. These parts can be damaged by static discharges.


The 555 and 556 timers are integrated circuits (IC) that need to be seated in the breadboard.  Look at the top of the IC (with pins held away from you) and locate the semicircular notch at one end. The locations of the pins are shown in the figure to the right. For the 556 timer, face the notch toward the right of the breadboard so that Pins 1 and 14 are also facing to the right. Now set pin 1 in hole 23F but don't push the pin into the hole yet. Set pin 14 in 23E. Line up all the legs with holes in the breadboard and then press as evenly as possible across the top of the IC in order to make sure that none of the pins are bent as the IC is seated.  Press firmly to make sure the pins go in as far as possible.


Now seat the 555 timer in a similar fashion. However, orient its notch facing to the left of the breadboard. Pin 1 will go in 2E.

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Step 2: Adding the Wires


These are the wires that will connect all your electronic components together. Since the wires run beneath the components (or around, in the case of the 555 and 556 timers, to allow for easier component removal), it is important to cut the wires so they lay flat against the breadboard. You can estimate how long a wire needs to be by running a piece between the two breadboard holes you want to connect, then cutting the wire 1/4" longer than that at either end. Then strip 1/4" of insulation from each end.


The list below will tell you which rows and columns your wire ends should fit into.


24E to (+) 28A to (-) 16E to 19G 25E to 25F 3D to 4G
20J to (+) 25A to (-) 19A to 24A 29E to 29F 5D to 2G
2J to (+) 9A to (-) 21D to 22D 27D to 29D 6E to 4H
  2A to (-) 23D to 24D 26J to 28J 11E to 13F
  17G to (-) 22G to 23G    
  7F to (-) 22J to blue column adjacent to the positive column    


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Step 3: Adding the Potentiometers


The delay unit includes two potentiometers for coarse and fine adjustment of the delay interval. First, find the blue 1-MΩ potentiometer, which will be used for coarse delay adjustment. Place the two front legs over 14J and 16J, and the rear leg over the nearest hole on the nearby (+) column. The front legs should be facing the center of the breadboard. Press the legs in firmly as far as they will go, but avoid bending them. (Note that the left leg will not be connected to anything else.)


Next is the brown 100-kΩ potentiometer, which will provide fine delay adjustment. Place the two front legs into 10I and 12I, and the rear leg over the nearest hole in the blue-lined column directly adjacent to the (+) column. Seat the potentiometer.


There are two potentiometers for sensitivity control. The yellow 1-kΩ potentiometer provides sensitivity adjustment for the sound trigger, and the white 10-kΩ potentiometer provides sensitivity adjustment for the photogate. Place the front legs of the yellow pot over 28F and 30F and the rear leg over 29J. Seat the potentiometer. Place the front legs of the white pot over 6A and 8A and the rear leg over the nearest hole on the negative column. Seat the potentiometer.


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Step 4: Adding the SCRs and the Transistor


SCR pin diagram


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

Transistor pin diagram

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

The output stage of each trigger and of the delay circuit are silicon-controlled rectifiers (SCRs) labeled EC103D. The SCRs act as electronic switches and allow you to to discharge a flash with or without a delay.  To identify the leads of an SCR, hold it as in the diagram to the right. Be careful not to confuse the SCRs with the transistor, which has the same shape and size but a different label.


Insert the SCRs in the locations below. Note that the legs of the two delay unit SCRs will have to be bent in order to reach the negative column.


  K G A
Photogate output 9B 10B 11B
Sound trigger output 28B 29B 30B
Immediate output of delay unit (-) column 12A 13A
Delayed output of delay unit (-) column 14A 15A


The transistor looks identical to the SCR but is labeled PN2222A (or 2N2222A). To identify the leads of the transistor, hold it as in the diagram to the above.  Put the emitter into 25B, the gate into 26B, and the collector into 27B.


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Step 5: Adding the Red LEDs


The red LEDs are used as inidicators. One of them indicates whether the emitter and detector of the photogate are aligned. The other indicates triggering of the delay unit. The polarity of the LED is indicated in two ways. (Click on the photo to see a larger version.)

  • The longer leg is positive.
  • The flat on the lip of the red case is on the same side as the shorter, negative leg.

Insert the LEDs as follows:


  long leg (+) short leg (-)
Photogate alignment indicator (+) column 8J
Delay triggering indicator red column adjacent to (-) column (-) column


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Step 6: Adding the Resistors


There are 14 resistors. Each resistor is marked with four bands that are a code for the value and tolerance of its resistance. Lay them out so that the gold band on each is always facing right (so it's the fourth band). The colors should now be read from left to right, ignoring the gold band.  In the following instructions, the resistors will be identified by the first three bands.  The gold band indicates the tolerance of the resistance value, while the other three bands indicated the value of the resistance.


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. 


Note that one of the 100-kΩ resistors will not be used in this step. The use of this resistor will be discussed in step 8, Changing the Reset Delay (also known at the timeout).


Value (Ω) Color Code Placements
100 brown-black-brown 4D to 10D 10G to 14G 12D to 16D 14C to 18C
470 yellow-violet-brown 1F to (-) 3H to 8H

18A to red column

adjacent to (-) column

22k red-red-orange 17B to 24B 18G to 20I    
1k brown-black-red 22C to 24C      
5.1k green-brown-red 26I to (+)      
100k brown-black-yellow 26D to 26G      
1M brown-black-green 13I to 18I      


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Don't be concerned if some of the capacitors shown in the photo have different physical sizes from those in your kit.  What is important is that the numbers on the capacitors are correct.

Step 7: Adding the Capacitors


First, gather together the capacitors. The ceramic capacitors have round, tan heads and do not have polarity. The electrolytic capacitors have cylindrical heads and do have polarity. Let's start with placement of the electrolytic capacitors.


Look at the cylindrical case and find the light-colored strip bearing a negative sign. The leg on the side of this strip is the negative leg, while the other lead is the positive lead.  Note that the positive leg is also the longer of the two legs. See this photo. Locate the 10-µf electrolytic capacitor, which will have 10 µf written on its case. Insert the positive lead into 22A. The negative lead will go to the nearest hole on the nearby (-) column. Now locate the 0.47-µf electrolytic capacitor. Insert the positive lead into 23H, and the negative lead into 25G.


Place the ceramic capacitors as follows:


Value (µf) Label Placement
0.0047 472 16A to 17A 13H to 18H
0.047 473 20A to (-) 17J to 21J
0.01 103 5J to 7J  


You should have two ceramic capacitors remaining.  These may be substituted for the 0.47-µf capacitor in order to obtain different delay ranges.  This will be discussed in the next step under Changing the Delay Range.



Step 8: Testing and Operating the Delay Unit


While the assembly isn't complete yet, you've done enough to be ready to test the delay unit. Do the following:

  1. Prepare a 3-inch long wire by stripping the insulation off the ends about a quarter of inch.

  2. Temporarily remove the wire from 11E to 13F. (You'll replace this in a later step.)

  3. Connect a fresh 9-V battery to the battery clip.

  4. Adjust the blue 1-MΩ potentiometer to its middle position.

  5. Push one end of the jumper wire (that you prepared in step 1) into 13F.

  6. Momentarily touch the other end of the jumper wire to the cathode of one of the SCRs (this is the leg that goes into the ground row). The delay unit indicator should blink on once after a short delay, indicating a successful triggering event.

If the test above wasn't successful, some possible reasons include the following.

  1. The battery isn't fresh.

  2. Wires or components are connected in the wrong holes.

  3. Legs of nearby components are touching each other.
  4. The electrolytic capacitors or indicator LED are connected with the wrong polarity or an SCR is connected in reverse orientation.

  5. The legs of the 556 timer or potentiometers aren't seated well in the breadboard.

  6. There's a break in the hookup wire or in the circuit.

Troubleshooting strategies include i) replacing the battery, ii) checking all connections and component placements, iii) checking for shorts (legs touching each other). In order to test for breaks in wires, jiggle the wires while touching the jumper wire to ground. An intermittent connection can sometimes be detected this way.


If you still can't get the circuit to work, it's possible that the 556 timer is burn out. In that case, check to see if your local electronics store carries the component, or contact us for a replacement 556.


Here are the operating instructions for the delay unit.


Making fine and coarse delay adjustments: The blue and brown potentiometers are used as variable resistors to set the delay. The blue 1-MΩ potentiometer provides coarse delay adjustment, while the brown 100-kΩ potentiometer provides a finer adjustment. Once you've set the delay approximately using the 1-MΩ potentiometer, use the 100-kΩ potentiometer to make finer adjustments. The further clockwise that you turn either potentiometer, the more of a delay there will be. You'll notice the delay as the time interval between connecting the jumper wire from 13F to ground and the flash of the red LED. If a flash unit were connected to the delayed output of the unit (more about this later), the flash would discharge after the delay that you dialed in.


Changing the delay range:  The circuit as currently wired provides a delay up to about half a second. This works well when using a photogate to detect the passage of a falling drop and then discharge a flash unit when the drop reaches the water's surface. For other applications, a much shorter delay may be required.  In order to provide fine adjustment of shorter delays, you can change the ranges of the potentiometers by removing the 0.47-µf capacitor and replacing it with one of smaller value.  The extra 0.1-µf and 0.01-µf capacitors are provided for this purpose.  The 0.1-µf capacitor will provide delays up to about a tenth of a second, while the 0.01-µf capacitor will provide delays up to about a hundredth of a second. You can use other values as well in order to customize your circuit. You can figure that the maximum delay in seconds is approximately equal to the value of the capacitance in microfarads.


Changing the reset delay: After the delay unit triggers, it will be inactive for a short time before it can be triggered again.  This amount of time is termed the reset delay.  The circuit is currently set for a reset delay of about a hundredth of a second.  (This is less than the recharge time of many flash units.)  For some photo situations, this may lead to multiple exposures.  In order to increase the reset delay, first locate the 1-kΩ resistor. Then replace it with the extra 100-kΩ resistor.  This will increase the reset delay to about a second. (The red LED will remain on during this time.) This replacement may also be necessary if your flash unit fires repeatedly in response to a single triggering event. You can use other values of the resistance in order to customize your circuit. You can figure that the reset delay in hundredths of seconds is approximately equal to the value of the resistance in kilohms. Thus, for a 100-kΩ resistor, the reset delay is about 100 x 0.01 s = 1 s.


One use of the reset delay is to eliminate multiple-exposures that may be produced by events having prolonged or multiple sounds. For example, if you're smashing glass, the initial breakage will produce one exposure while the sounds of glass hitting the table may produce additional exposures. If you set the reset delay to a second, you'll get just one exposure.


Here's another way to use the reset delay if your flash unit has a strobe function; that is, you can set the flash to fire a burst of flashes in quick succession. If you use a very short reset delay, you'll get just one flash. But if you increase the reset delay to, say, a second, you'll trigger the entire burst. This idea comes from DIYer Allen Hart.

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Step 9: Adding the Piezoelectric Element

Disconnect the battery before continuing below.


If you haven't already prepared the microphone cable, see these instructions and then return here.


Connect one wire from the microphone to 26A and the other wire to the nearest hole in the negative column. Polarity does not matter.


Step 10: Preparing the Output Cable and Testing the Sound Trigger


A trigger cable is needed to connect your flash unit to the breadboard.. The trigger cable kit is purchased separately, since there are different connectors depending on your flash unit. If you need a trigger cable kit, see this page. Follow the instructions for assembling the flash trigger cable from your kit.


Testing the sound trigger: Turn the yellow potentiometer all the way clockwise. Then connect the red and black wires of the output cable to these locations: red to 30A and black to the ground (-) row. Connect your flash unit to the other end of the output cable. Connect the 9-V battery to the circuit. A finger snap or a tap on the piezo disc should set off your flash immediately. The only delay is the amount of time it takes sound to travel from the source of sound to the microphone. That's about a thousandth of a second per foot (30 cm) of distance.


Adjusting the sensitivity: You can increase the sensitivity by turning the yellow pot counterclockwise. Beyond a certain point, typically about the halfway point, the flash will go off spontaneously. When you reach that point, turn the knob clockwise until the flash discharges with a finger snap. This is the point of maximum sensitivity.



Step 11: Preparing the Photogate Cables and Testing the Photogate


Your kit includes parts for two types of photogate cables. What we call SPG1 has an individual emitter and detector. This is useful when you need large separations between the emitter and detector. The SPG2 cable uses an interrupter, which houses the emitter and detector in a U-shaped plastic housing about 5/8" apart. This is useful for triggering on the passage of a drop of liquid.


The gray, six-foot, 3-conductor cable supplied with your kit will be used for both photogate cables. Begin by cutting it into 2 equal lengths.


The instructions for preparing the photogate cables are given at the links below. Assemble the SPG1 cable first and then return to this page. You can assemble the SPG2 cable later.


SPG1 cable

SPG2 cable


Testing the direct output of the photogate: You should now have the free ends of the 3-conductor cable connected to these holes on your breadboard:

Black to 1J
Green to 4J
Red to the (+) column

Now connect the output cable that you prepared in step 10 to these locations:

Red to 11A

Black to ground

Align your photogate if it isn't that way already and run your finger through the gate. The flash unit should discharge immediately.


Adjusting the sensitivity: First align the photogate and make sure it's working. Then turn the white knob clockwise until the photogate indicator LED goes off. Back off the knob a little bit until the LED comes back on. If you change the distance between the photogate emitter and detector (if using the individual components) or if the orientation of either component changes slightly, you may need to readjust the sensitivity.  The maximum separation is about 6 inches. The larger the separation, the more care you need to take in aligning the components. If you wish to have greater separation, a red laser pointer can be used instead of the IR LED.


For some applications, it’s desirable to have a large working distance between the emitter and detector of the photogate. Use a red laser pointer as the light source on the detector. (You'll need to use the SPG1 cable for this and tape the emitter out of the way.) Note that if the beam is too intense, you may have trouble adjusting the photogate sensitivity (see bottom of the next page). In that case, try reducing the beam intensity either by placing a neutral-density filter over the LED or poking a hole in a piece of aluminum foil and placing that over the LED.


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Step 12: Using the Delay Unit with Sound or Photogate Trigger Input


Testing the photogate with the delay unit: In step 8, you removed the wire from 11E to 13F. Replace it now. This is the wire that connects the output of the photogate to the input of the delay unit.


Next move the red wire of the output cable to location 13B. You can leave the black wire in the ground column. These are the connections for the immediate output of the delay unit. Align the photogate and pass your finger through it. Both the delay unit indicator LED and your flash unit should flash immediately.


Next move the red wire of the output cable to location 15B. Again, leave the black wire where it is. These are the connections for the delayed output of the delay unit. (The photo to the left shows the photogate cable connection and also the output cable connected to the delayed output.) Turn the coarse delay (blue knob) at least half of its travel clockwise. Align the photogate and pass your finger through it. This time, the indicator LED and flash unit should flash after a short but noticeable delay.


Testing the sound trigger with the delay unit: Remove the wire from 11E to 13F. Take the 3" jumper wire that you prepared in step 8 and connect it from 13F to 30A. This will connect the output of the sound trigger to the input of the delay unit.


Leave the red wire of the output cable in location 15B and the black wire in the ground column. When you snap your fingers near the sound trigger, the delay unit indicator LED and the flash unit should flash after a noticeable delay. If you don't get a flash discharge, turn the yellow pot three-fourths of the way clockwise. The sound trigger isn’t as sensitive when used with the delay unit; however, this shouldn’t be a problem since the microphone needn’t be placed far from the source of the sound when setting delays electronically.


Don't connect both the sound trigger and photogate outputs to the delay unit input at the same time. The unit may not function with both connected.


If you're connecting to the direct output of the photogate or sound trigger, disconnect the jumper wire from the output of the trigger to the input of the delay unit. This is the wire from 11E to 13F for the photogate and 30E to 13F for the sound trigger. If this wire is left in place, some flash units can burn out the 556 timer.


You may have the piezoelectric element and the photogate connected to the breadboard at the same time. If, however, you want to conserve your battery, disconnect the transducer that you're not using at the time.


Disconnect the battery when not in use. The circuit will eventually drain the battery if left connected for long periods of time. Disconnect the battery when the circuit is not in use. You may also choose to use a 9-V AC/DC adapter to power the unit. Any AC/DC adapter that provides up to an ampere of direct current at 9 V should do. Here’s an example.


The red and black wires of the completed cable connect to the breadboard as follows for the indicated outputs.


red wire
black wire
Photogate direct
ground (-) column
Immediate output of delay unit
ground (-) column
Delayed output of delay unit
ground (-) column


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Summary of Cable Connections


Click on the thumbnail on the left for a high-resolution photo of the completed circuit with annotations. Below is a list of the connections of the transducers and output cable to the breadboard.


red wire
black wire
green wire
Battery cable red (+) column

black (-)


Piezoelectric element ground (-) column 26A  
Photogate cable

positive (+)


1J 4J
Sound trigger direct output 30A ground (-) column  

Photogate direct output

ground (-) column
Immediate output of delay unit
ground (-) column
Delayed output of delay unit
ground (-) column



Connecting a Trigger Circuit to a Camera or Wireless Transmitter


Connection to a camera


If your camera has an electronic shutter with a remote cable, you can actuate the shutter using an output of your trigger circuit. This is a useful thing to be able to do if you're, say, photographing insects, birds, or other unpredictable subjects. You simply can't hold the shutter open waiting for the subject to appear. Another application where it's useful to trigger a camera is in splash photography. The immediate output of a delay unit can be used to trigger the camera and the delayed output to trigger a flash unit. The camera exposure time can be set so that the shutter remains open just long enough for the splash event to be completed.


If you wish to connect the trigger to your camera shutter, there are two options.


COS option: Build the Camera Opto-Switch. Then connect the trigger output cable to the breadboard according to the table here.


DIY option: Prepare a camera cable according to the instructions here. Then connect the trigger output cable to the breadboard according to the table here (same as for a flash unit).


Connection to a wireless transmitter


Wireless transmitters such as PocketWizards can be triggered from your trigger circuit the same as you would trigger a flash unit. Just connect to the transmitter using either a PC cable or hot shoe adapter.


Assembly instructions for other kits




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