information and inspiration
for students, teachers and hobbyists
About Tools Products Activities Galleries Projects Links Contact Facebook LinkedIn  flickr


Assembly and Operating Instructions for Kits


Assembly Instructions for the Multi-Trigger 3+ (MT3+)


Assembly instructions for other kits




Building the control box

What you need

Parts guide and schematic

Soldering the fixed-value resistors to the PCB

Soldering the IC sockets to the PCB

Soldering the capacitors to the PCB

Soldering the semiconductors and the fuse holder to the PCB

Soldering the fuse holder to the PCB

Drilling holes in the project box lid

Adding the label for the lid

Adding the components to the project box lid

Wiring the box lid

Soldering and connecting to the PCB
Testing the timing functions

Preparing the cables (opens in a new tab)


This page provides the instructions for assembling the control box of the Multi-Trigger 3+. At the completion of this assembly, a series of tests of timing functions of the box are described. Afterwards, you'll go on to preparing the trigger and flash cables. Then there will be another series of tests of the inputs and outputs.


About the images: Clicking on any image will open a larger version on top of the page. If you prefer to have the larger images open in a different tab or window, right click on the image and make the appropriate selection.


What you need

PCB for Multi-Trigger 3+ PCB for Multi-Trigger 3+
Top Bottom


These instructions show how to prepare and use the PC board and project box enclosure for the Multi-Trigger 3+. The MT3+ comes complete with all the parts needed for assembly of a working Multi-Trigger 3+ on a PC board enclosed in a project box. Parts are included for microphone and interrupter photogate cables.


The to and bottom sides of the PC board are shown to the right. You'll see that the locations for the components are labeled with symbols like R2, C1, etc. This makes it easy to find where to place the components.


You'll need to solder the components to the bottom side of the PCB. We'll provide guidelines for getting good solder joints, but we recommend that you have previous experience soldering on a PC board. If you solder something in the wrong place, repair can be time-consuming.


Having the right tools will make the job easier. You'll need to provide your own. Here's what we recommend.


For soldering

  • 15-30 W soldering iron (with a new or pointed tip) and solder
  • Wire stripper (photo below)
  • A small diagonal cutter (photo below) makes it easy to trim the legs of the components after you solder them to the PCB, but other kinds of snipping tools such as scissors may work.
  • Needle-nose pliers (photo below) make it easier to handle small components, especially if you have big fingers.
  • A desoldering tool (photos below) helps in clearing solder from a hole. The cylindrical type works better than the bulb.
  • A magnifying glass is used to inspect solder joints.
  • A lighter or matches to shrink heat-shrink tubing
    Wire cutters and stripper Small diagonal cutter Needle-nose pliers Desoldering tools



    diagonal cutter


    needle-nose pliers

    desoldering tool desoldering bulb


Solder in a well-ventilated area. Keep the tip of your soldering iron clean by wiping it against a wet sponge. Once the tip is clean, touch a bit of solder to the tip to tin it and improve heat conductivity. Inspect your solder joints to see if the solder flowed well to make good electrical contact. If it looks like the solder formed a bead, that's likely a bad joint and will not conduct. Reheat to flow the solder.


For the project box components

  • Drill motor and bits to drill holes in the project box lid. Bit sizes are 3/32", 1/8", 1/4", 5/16", and 3/8". (For metric equivalents in millimeters, multiply by 25.) You can substitute a 1/8" bit for the 3/32" one.
  • Hammer, punch (or nail), small round file
  • Wrenches or sockets to tighten components onto the project box

For the label

  • Scissors or stencil knife and straightedge to cut out the label
  • Stencil knife or razor blade to cut out the holes
  • 1/4" hole punch (not required but helpful)
  • Masking or blue tape
  • Glue such as contact cement or spray adhesive. (Elmer's Rubber Cement, shown below, works well.)

desoldering bulb


For the knobs

  • A jeweler's screwdriver to tighten the set screws (in a pinch, the tip of a knife blade will do)

Aids to troubleshooting


If you need to troubleshoot problems with the circuit, it will help to have at least some basic skills in building and testing electrical circuits. These involve such things as testing for polarity and continuity, for examining solder connections, and for measuring voltages. In addition to such knowledge and exerience, having a continuity checker or multimeter and clip wires may be helpful.


Parts guide and schematic


Click here for a detailed, illustrated list of all the parts you'll need. Here's a condensed version for printing. If you like referring to a circuit schematic, you may open one here for printing.


Before starting work in each section, we recommend reading through the section completely in order to get an overview of what you'll be doing.


Soldering the fixed-value resistors to the PCB


If you don't have your soldering iron heated up, do that now, because you'll be soldering before long. You'll be doing some detailed soldering work, so an iron with a good tip will make it easier. You'll solder resistors R1, R7, and R10 directly to components on the lid of the project box; therefore, set those resistors aside for now. We'll start with R2, a 5.1-kilohm (kΩ) resistor that will be soldered to the PCB. See Figure 1 and refer to the Parts Guide as needed for parts to come. The resistors are identified by the sequence of 3 colored bands, read from left-to-right. (The 4th, gold band indicates that the actual value of the resistance is plus or minus 5% of the value given by the color code.) For the resistor shown in Figure 1, the bands are green-brown-red.

  1. Insert the legs of resistor R2 over the rectangular space labeled R2 on the PCB. See Figure 2. You can flip the resistor either way in the holes; the orientation doesn't matter for resistors, since resistors work the same no matter which way current flows in them.

  2. Push the resistor in until it's flush with the surface of the PCB. Then flip the PCB over. Figure 3 shows the legs protruding from the back of the board.

  3. Next you'll solder. Tin the tip of the soldering iron by melting some solder on it. Then bring the point and the solder down to one of the holes where the resistor protrudes. Melt some solder around the base; it doesn't take much. The solder should flow down into the hole around the leg of the resistor to make a good electrical joint. Now solder the other leg.

  4. Snip off the legs of the resistor. The completed solder joints are shown in Figure 4. If you don't see that solder melted through to the upper side, it's probably a good idea to melt some more solder into the hole from the back of the board.

  5. Something to be aware of before you do any more soldering is that there are two kinds of holes on the board: solder holes and via holes. The solder holes are for the component legs. The via holes, which are slightly smaller than the solder holes, are places where there are connections between the upper and lower conducting layers of the board. To see what we mean, see Figure 5, which shows a small section of the board. Two via holes have been circled in yellow. Don't try to solder components into a via hole. (If, however, you get solder in a via hole, that won't hurt anything.)

  6. Solder the remaining resistors (exclusive of R1, R7, and R10) onto the board. The result is shown in Figures 6 and 7 for both sides of the board.

5.1 kohm resistor
Figure 1. 5.1-kΩ resistor Figure 2. Resistor R2 inserted into dedicated space on PCB Figure 3. Legs of resistor R2 protruding from underside of PCB Figure 4. Completed solder joints from the underside
Figure 5. Via holes (circled in yellow) Figure 6. PC board with all resistors mounted Figure 7. Under side of PC board with all resistors mounted  


Back to top


Soldering the IC sockets to the PCB


The 8-pin, 14-pin, and 16-pin IC sockets will be used to seat the four ICs. The latter won't be added to the sockets until later, since the ICs can potentially be damaged by heat.

  1. See Figure 8, which shows one of the 8-pin sockets next to the location where it will be mounted. Note that the socket has a notch on one end. Line this notch up with the one on the PCB when you seat the socket into the board.

  2. Place the 8 pins of the socket into the corresponding holes on the PCB as shown in Figure 9.

  3. Turn the board over and bend the pins down to the side to hold the socket in place as shown in Figure 10.

  4. Solder the 8 pins to the board. Avoid the via hole as shown in Figure 11. Check with a magnifying glass to make sure there are no solder bridges or hairs between pins. If so, remove them by running the tip of the soldering iron between the pin.

  5. Solder the pins of the 14-pin socket next. Remember to line up the notches. Figure 12 shows two via holes to avoid (circled in yellow).
  6. Finally, solder the 16-pin socket and the other 8-pin socket to the board. Figure 13 shows the back of the board with all sockets soldered into place, while Figure 14 shows the top of the board.

Figure 8. Notches on the socket and the PCB Figure 9. 8-pin socket seated on PCB Figure 10. Crimping the pins of the 8-pin socket Figure 11. 8-pin socket soldered to PCB
Figure 12. The 14-pin socket soldered in place. Figure 13. All sockets soldered to under side of PCB Figure 14. All sockets and resistors soldered to upper side of PCB  


Back to top


Soldering the capacitors to the PCB


There are two kinds of capacitors, ceramic and electrolytic. We'll start with a ceramic capacitor. There are 7 of these; they all have a disc shape and are orange or yellow in color. A number on the disc identifies the capacitor. The capacitor in Figure 15, for example, has the number 473 (473M represents the same value). From the Parts Guide, you can determine that this is a 0.047-μf capacitor.

  1. Refer to Parts Guide to see which capacitors are associated with C1, C2, etc. on the PCB. C1 is a 0.047-μf capacitor. Figure 16 shows the capacitor lying over the corresponding location on the PCB. Slip C1 into the holes now as shown in Figure 17. Ceramic capacitors, like resistors, are non-polar. So it doesn't matter if you flip them one way or the other in the solder holes. The legs should extend about 1/8" from the top side of the board. Bend the legs over on the back to keep the capacitor from slipping out when you turn the board over. The soldered capacitor is shown in Figure 18 from both the upper and lower sides of the board. Check for solder bridges like you did for the IC sockets.
  2. Next you'll solder an electrolytic capacitor. There are 3 of these. The electrolytical capacitors have cylindrical metal cases with the value of the capacitance printed on them. These capacitors are polar; that is, they have a positive and negative side. Therefore, there's only one correct way to mount them in the PCB. See the photo of two sides of a 0.47-μf capacitor in Figure 19. (This is capacitor C3.) The shorter leg is negative and corresponds with the light-colored strip on the case. Now look at Figure 20, which shows the C3 capacitor inserted into its mounting holes on the PCB. Note that the location of the hole for the positive leg is marked on the PCB with a + sign. See Figure 21 for the alignment of the negative side. When soldering this and the other two electrolytic capacitors, don't let the legs extend more than 1/8" from the top of the board. Otherwise, when you mount the PCB to the project lid later, you may not be able to fit the lid snugly onto the box. Go ahead now and solder the legs of C3 to the board.
  3. Solder the remaining capacitors to the board. Note that two of them are labeled BC1 and BC2. Note also that the 0.0047-μf capacitor may be labeled 472 or 472M. Figure 22 shows all capacitors soldered to the board.
  4. If you haven't snipped off the legs of the capacitors protruding from the back, do that now. Snip them at the solder joint. You don't want to have any legs that can be bent over and touch other legs to create short circuits.
0.047-uf capacitor
Figure 15. 0.047-μf ceramic capacitor Figure 16. C1 capacitor next to mounting holes Figure 17. C1 slipped into holes on PCB Figure 18. C1 soldered to PCB, from above and below
Two views of a 0.47-μf electrolytic capacitor
Figure 19. Two views of a 0.47-μf electrolytic capacitor Figure 20. C3 capacitor in mounting holes Figure 21. C3 capacitor showing negative marking Figure 22. Board with all resistors, capacitors, and sockets


Back to top


Soldering the semiconductors and the fuse holder to the PCB

  1. There is one transistor, labeled PN2222A, and there are four silicon-controlled rectifiers (SCR), labeled EC103D. You'll solder the transistor first. Note the orientation of the flat side of the transistor as shown in Figure 23. The flat side is toward SCR4. Push in the transistor so that about 1/8 inch of the legs extend above the surface. Note that the legs of the transistor are closer together than any other component, so you'll need to be particularly careful to avoid solder bridges. See Figures 24 and 25 for the completed soldering.

  2. Next you'll mount SCR1. Note the orientation of the flat side of the component in Figure 26. The flat side of the SCR corresponds to the footprint on the PCB. Like the transistor, push in the component so that about 1/8 inch of the legs extend above the surface.

  3. Solder the remaining SCRs. Figure 27 shows all four SCRs in place.

  4. If you haven't already snipped the legs of the SCRs extending under the board, do that now.

  5. The last component to solder to the board is the fuse holder. It'll take a bit of force to snap the 2 legs into place. Once in place, solder the legs. Figure 28 shows the board with all components in place with the exception of the ICs and fuse, which will be added as the final step. The under side of the board is shown in Figure 29.
Figure 23. Orienting the transistor Figure 24. Transistor soldered to the PCB (bottom view) Figure 25. Transistor soldered to the PCB (top view) Figure 26. SCR1 oriented on the PCB
Figure 27. PCB with all SCRs mounted Figure 28. PCB with fuse holder mounted Figure 29. Under side of PCB with all components mounted  


Back to top


Drilling holes in the project box lid

  1. The drilling template is sized to fit snugly within the under side of the project box lid (that is, on the interior side of the box). Position the template inside the lid as shown in Figure 30. Then use a nail or punch to mark the positions of the centers of the holes to be drilled. Figure 31 shows the underside of the lid with the template removed, showing the pit marks of the punch.

  2. Remove the template and drill the holes. We recommend drilling small pilot holes first, for example, 3/32" (3 mm). Figure 32 shows the interior of the lid with all pilot holes drilled.

  3. Now drill all the holes larger than 3/32". The plastic has a tendency to grab the bit, so hold the plastic securely. We've found that spade bits work best for drilling the 1/4" and 5/16" holes. Figure 33 shows the outer view of the lid with all holes drilled. Note that the hole for the pushbutton is circled in yellow. The pushbutton actually requires a hole slightly larger than 1/4". Use a round file to enlarge this hole so that the pushbutton will fit.

  4. Use the file to clean up any burrs around the holes.
Figure 30. Template placed in underside of project box lid Figure 31. Lid with positions of holes marked by punch Figure 32. Lid with 3/32" (3 mm) pilot holes drilled (interior view) Figure 33. Interior side of box lid after holes drilled


Back to top


Adding the label for the lid

  1. Figure 34 shows the lid label. Trim the edges to the black border, but before trimming, see Figure 35, which shows the label as it will be placed on the top of the lid. Note how the label is trimmed so that the corners don't interfere with the mounting holes. We recommend using a stencil knife with a ruler or straightedge in order to get clean lines when you trim. However, a pair of sharp scissors will work, too.
  2. Next you'll laminate the label. This will help protect it from marks and scratches. Two laminating sheets are provided. Remove the paper back from one of the sheets and gently press the label face down onto the sticky side of the laminate film. See Figure 36.
  3. Turn the label over. Remove the paper backing from the other sheet of laminate and stick the back side of the label down onto the laminate. Smooth out any air bubbles. Then trim the laminate away around the borders of the label, leaving about 1/16" (1 mm) of the laminate protruding around the edges of the label. This allows to the two sheets of film to hold together on the edges. See Figure 37 for the completed lamination.

Carry out this alignment procedure before you glue the label to the lid

  1. In order to help in aligning the label with the holes drilled in the lid, punch or cut some alignment holes. A 1/4" hole punch works well for this. You can punch out all the 1/4" and 5/16" holes around the periphery of the label. See Figures 38 and 39. If you don't have a punch, you could use a stencil knife or razor blade. Don't worry if the edges of the holes are a bit ragged. This will be covered when you mount the components later.

  2. Now place the label on the lid with the 1/4" holes of the label aligned with those drilled on the lid. Next cut the 2 inches of 1/4" OD plastic tubing provided with your kit into two 1" lengths. Push these into diagonally opposite corner holes to check the alignment of the label with the holes in the lid. See Figure 40.

  3. Once you've checked the alignment, remove the tubing and the label. Gluing will be next.

  1. Now you're ready to glue using a spray or contact adhesive. We recommend using Elmer's Rubber Cement, because it's easy to remove any over spread. Apply the adhesive uniformly on the lid and the back of the label. Depending on the adhesive that you use, you may have to wait several minutes before pressing the label onto the lid. When you do, make sure the holes align. If you use a removable adhesive like Elmer's Rubber Cement, then you can rub off any excuse glue with a finger. You can also use denatured alcohol and a soft, clean cloth to remove any glue on the label itself. At this point, we recommend stacking some books on top of the lid to press the label firmly into place for about an hour.
  2. After the glue has set, you can cut out the rest of the holes. We recommend using a small stencil knife as shown in Figure 41. Don't use a drill bit for this, as that will rough up the edges of the holes too much. Alternatively, you can cut the holes out from the underside of the lid as shown in Figure 42. After cutting out the holes,work the knife blade around the inside of each hole to ream out any overlapping paper. This will allow components to be slipped easier. Getting clean holes for the 4 LED holders is particularly important. If the holes are too small, even just slightly, it will be more difficult to push in the LEDs later.
  3. For the four 1/8" holes that will be used to mount the PCB, you can can push through the label with the point of a pencil or the shaft of a jeweler's screwdriver as shown in Figure 43. Again, don't worry about the edges being ragged or curled. They'll be covered by bolt heads later.
  4. The completed label glued to the lid with all holes cut out is shown in Figure 44.
Figure 34. Label for the lid Figure 35. Label placed on the lid Figure 36. Placing the label face down on the laminate Figure 37. Lamination complete

Figure 38. Punching the 1/4" holes for alignment Figure 39. Label with holes punched Figure 40. Plastic tubing aligns 1/4" holes of label with those on lid Figure 41.Cutting out a hole with a stencil knife
Figure 42. Cutting out a hole with a stencil knife (from the inside) Figure 43. Cutting out a hole with a stencil knife (from the inside) Figure 44. The completed label will all holes cut out  


Back to top


Adding the components to the project box lid

  1. The graphic in Figure 45 will be helpful in placing the components. Click on the image to open it in a new tab. Then you can print it or just have it available for reference in a separate tab of your browser. Note that the view is from the under side of the box lid. The symbols for the components are the same as in the list provided here.

  2. Start with the pushbutton. Mount it in the position for Test using the lock washer and nut. The component circled in yellow in Figure 46 is the pushbutton as seen from the underside of the lid. The view of the mounted pushbutton from the upper side is shown in Figure 47.

  3. Before mounting the switches, it's important to distinguish between two types. These are shown in Figure 48. Enlarge each image to get a close look at the metal plate on the side. One plate says ON ON and the other ON OFF ON. In your kit, there should be two of the ON ON switches and one of the ON OFF ON type. We'll use these names to distinguish the switches in the instructions that follow.
  4. FIgure 49 shows a switch with the washers, nuts, and rings removed. (This applies to all the switches.) The guide ring to the lower right in the photo has a tab that is used to keep the switch from twisting. Typically, this is placed on the top of the lid; however, we're putting it on the bottom. That's to avoid having the guide holes show on the label. See Figures 50 and 51 for how the ring for Switch 2 is positioned. This is where you will place the ON OFF ON switch. Insert the switch and screw it in place using the washer and one nut on the top of the lid. The second nut won't be used. Repeat the process with the two ON ON switches in the Switch 1 and 3 positions. The three mounted switches are shown in Figure 52 from the under side of the lid and in Figure 53 from the upper side.
  5. The RCA jacks are next. There are three of these. The placement of one of them is shown in Figure 54. Note how the tab on the side is oriented away from the switches. Screw this jack into place and then add the other two RCA jacks as shown in Figure 55 with the tabs pointing toward the switches. The upper side with jacks mounted is shown in Figure 56.
  6. The 3.5-mm jacks are next. The gray or cream-colored jacks are mono, and the black ones are stereo. Simply remove the nut, insert the jack, put the nut back on and tighten. Figure 57 shows all of the black 3.5-mm stereo jacks in place. For each jack, note the orientation of the lug that extends from the side. While the orientation isn't critical, it will make wiring easier later on. Next mount the 4 mono jacks as shown in Figure 58. The view from of upper side is shown in Figure 59.

  7. The last jack to mount is the power jack. Figure 60 shows a close up of this jack in place in the lower right-hand corner of the lid. Note the orientation of the 3 lugs. While this orientation isn't critical, using the same orientation as in the photo may help in keeping straight the wiring to the 3 lugs, which can be confusing otherwise.
Figure 45. Parts placement (from under side of lid) Figure 46. The pushbutton mounted (from under side) Figure 47. Pushbutton mounted (from upper side) Figure 48. Two types of switches
Switch with various parts removed
Figure 49. Switch with the various parts removed Figure 50. See the next photo for a close up of the region in the yellow rectangle Figure 51. Orientation of the tab on the switch ring Figure 52. Three switches mounted (under side)
Figure 53. Three switches mounted (upper side) Figure 54. Mounted RCA jack Figure 55. All RCA jacks mounted (under side) Figure 56. All RCA jacks mounted (upper side)
Figure 57. Black, 3.5-mm stereo jacks mounted Figure 58. All 3.5-mm jacks mounted (under side) Figure 59. Switches and all jacks mounted to the lid Figure 60. Close up of power jack placement
  1. The next step is to add the LEDs. The LED mounts have two parts, which we will call the collar and the ring. See Figure 61. The collar is first slipped into a hole on the project box from the top side toward the interior of the box and snapped into place. If you have trouble forcing a collar through the hole, try widening the hole by scraping out any label overhang. Figures 62 and 63 show the 4 collars mounted from the under and upper sides of the lid.

  2. With the collars in place, an LED is pushed into each collar from below. Orient the LEDs so that the longer of the two legs is toward the outside of the lid as shown in Figure 64. It's important to get the LEDs to snap into the collars. It will take some extra force to push the LED in the last bit of the way. You'll know it's in when it snaps. If you don't push the LED in all the way, it will be loose in the collar. Figure 65 shows how the LED should appear from the side.

  3. Once you have the LEDs snapped in, push the rings over the collars from below. See Figure 66 for the completed assembly showing the rings. Figure 67 shows the lid with all components mounted so far.

  4. What remains is to mount the 3 variable resistors (also called potentiometers or pots, for short). Note that the value of each pot is stamped in white on the face of the pot. (See Figure 68, for example, which shows B1M. This is a 1M pot.) Each of the pots has a tab which is inserted into the corresponding guide hole on the lid. We recommend snipping off about one-third the length of the tabs as shown in FIgure 68. This prevents a tab from pushing up against the label on the lid. Be sure to mount the pots in the correct holes in the lid. (Figure 69 shows the correct arrangement.) When you remove the nut, you'll find two washers. You can put one below the lid and one above. When you tighten down the nut, don't overtighten as that could impede the operation of the pot. The lid with all components mounted so far is shown in Figure 70.
  5. In order to add a knob to the shaft of a pot, first turn the shaft of the pot all the way counterclockwise. When you seat the knob on the shaft, orient the white marker with 0 on the time scale. Then tighten the set screw. (If you find that it's difficult to push a knob onto a shaft, there may be a burr around the set screw hole on the inside of the knob. If so, use a round file to remove the burr. That should take care of the problem.) With all the knobs in place, the box is shown in Figure 71.
  6. The last parts to add to the lid are the bolts and standoffs. Push 4 of the 4-40 bolts through the 1/8" holes on the lid. See Figure 72, which shows the bolts circled in yellow from the upper side. Screw the standoffs onto the bolts. The result is shown in Figures 73 and 74. This completes the mounting of the components on the lid.
LED holder
Figure 61. Parts of an LED holder Figure 62. Collars of the LED mounts snapped into place Figure 63. LED collars in place (from upper side) Figure 64. The four LEDs with longer legs toward the outside
Trimming the height of a tab
Figure 65. The seated LEDs from the side Figure 66. LEDs mounted with rings in place Figure 67. LEDs mounted (upper side) Figure 68. Trimming the height of a tab
Figure 69. The three variable resistors with values in yellow Figure 70. All components mounted, exclusive of knobs and standoffs Figure 71. Lid with knobs bolted into place Figure 72. Bolts for standoffs circled in yellow
Figure 73. The four standoffs from the under side of the lid Figure 74. Under side of box (diagonal view)    


Back to top


Wiring the box lid


We will be using the following number scheme for the lugs of the components. The photos of the 3.5mm jacks are inverted below, since you'll view them upside down as you wire them on the lid. The switch is shown from the side to show that lug 1 is on the same side as the alignment tab. Note that this applies to both types of switches. This wiring guide will serve as a helpful reference as you do the wiring.

power jack 3.5mm mono jack (inverted) 3.5mm stereo jack (inverted) variable resistor switch
Power jack 3.5mm mono jack 3.5 mm stereo jack variable resistor Switch


Some of the components on the box lid will be hardwired to each other. Make connections now but don't do any soldering yet.

  1. There are three resistors that are connected between components on the lid. We'll start with the 1-kΩ resistor (brown-black-red) labeled R7 in the component list. See Figure 75 for the placement of the resistor. Connect it from the left lug (1) on pot RV4 to the center lug (2) of RV3. Note how the legs of the resistor are bowed away from the pots in order to eliminate the possibility that a resistor leg touch one of the other legs of the pots.

  2. Connect resistor R2 (5.1 kΩ, green-brown-red) from lug 1 of the photogate in jack (J1) to lug 1 of the auxiliary in jack (J2) as shown in Figure 76. You'll need to trim the legs of the resistor in order to fit it in the space available.
  3. Connect resistor R10 (1 kΩ) from lug 1 of J2 to the shorter leg of LED1 as shown in Figure 77. In order to make the connection to the leg of the LED, it's helpful to first wrap one end of the reistor around a small nail or brad as shown in Figure 78. Then slip the helix thus formed onto the leg as shown in Figure 79.
Wire wrapping
Figure 75. 1-kΩ resistor wired between RV3 and RV4 Figure 76. 5.1-kΩ resistor wired between side lugs of jacks J1 and J2. Figure 77.1-kΩ resistor wired between side lug of J2 and shorter leg of LED1 Figure 78. Wrapping a resistor leg around a nail
Figure 79. Close up of the wire wrap Figure 80. Ground (white) wires added to the lid Figure 81. Power (red) wires added to the lid Figure 82. Green and blue wires added to the lid
  1. The lengths of wire provided in the kit assume that you use the same colors as given in these instructions. You'll be clipping off lengths of wire and making the connections shown in the figures to come. These connections are also shown in the graphic supplied on the second page of the aforementioned wiring guide. Begin with the white wire, which is used for ground connections. A list of connections is provided in the table below and shown in Figure 80 above.
Letter on Figure 80 Connection

lug 1 of auxiliary in jack (J2)

B lug 1 of microphone jack (J9)
C side lug of instant pulse jack (J4)
D bottom lug of test pushbutton (PB1)
E side lug of delayed pulse jack (J10)
F lug 1 of instant flash jack (J7)
G lug 1 of delayed flash jack (J8)
H shorter leg of LED4
I shorter leg of LED3
  1. The red wire is used for connections to the power source. Connect those wires next. A list of connections is provided in the table below and shown in Figure 81 above.
Letter on Figure 60 Connection
J lug 3 of power in jack (J3)

lug 3 of photogate in jack (J1)

L longer leg of LED1
M longer leg of LED2
N lug 1 of RV2
O lug 1 of RV3
  1. There are 3 green wires and 1 blue wire to connect between components on the lid. The connections are given in table below and shown in Figure 82 above.
Color Connect from Connect to
green P lug 2 of power in jack (J3) Q

lug 2 of SW1

R lug 2 of auxiliary in jack (J2) S lug 2 of SW2
T lug 2 of SW3 U lug 2 of RV4
blue V upper lug of test pushbutton (PB1) W lug 3 of auxiliary in jack (J2)

Back to top


Soldering and connecting to the PCB


It's time to start soldering. Here are some important tips about soldering in addition to those given previously.


Soldering to the legs of the LEDs: Solder the connection near the base of a leg about a quarter inch from the plastic. If you solder way out on the end, then you increase the chances that the two legs will touch each other or the PCB and create a short when the box is assembled.


Soldering the switches: Don't hold the soldering iron on the switch lugs too long, as the plastic can melt and break the internal contacts.


Soldering the 3.5mm jacks: The lugs on these jacks bend and break easily. Go easy on them.


Soldering the power jack: Be very careful not to get too much solder on the lugs so that the solder drips down, particularly on the center lug. If the solder drips down, it can create a dead short between the positive and negative power terminals.


About cold solder joints: If you don't heat the metal before soldering the wire, the solder may not bond with it and you can get an open circuit. You can't necessarily tell by looking that you have a cold solder joint. The best approach is prevention by using good soldering techniques. Hold the tip of the soldering iron flat against the metal surface that you're soldering to. Touch the solder to the metal nearby rather than to the soldering iron. When the metal is hot enough, the solder will flow. Flow enough solder on the connection to fill the hole and cover the connection, but don't leave the soldering iron on the metal any longer than it takes to flow the solder. Examine the connection under a magnifying glass. If the solder beaded up, you may not have a good connection.

  1. You may now solder all but 4 of the connections on the lid. The 4 connections not to solder are indicated with an X in Figure 83and listed in the table below. These 4 connections will each have a wire added later for connections to the PCB.
Connections not to solder

lug 3 of power in jack (J3)

lug 3 of auxiliary in jack (J2)
lug 1 of delayed flash jack (J8)
lug 2 of variable resistor, RV4

The standoffs insulated with electrical tape
Figure 83. Connections not to solder (marked with X) Figure 84. Jumper wires connected to the lid (except for one marked X)

Figure 85.The standoffs insulated with electrical tape

Figure 86. Jumper wires with stick-on labels
  1. Refer to the table given on page 1 of the wiring guide for the lengths of the wires to cut for the connections between the lid and the PCB. Before soldering the connections, we recommend cutting the wires to the lengths given in the table. The lengths are sized to be long enough to reach the corresponding holes on the PCB but not so long as to add unnecessarily to the mass of wires that will have to be compressed when the PCB is finally bolted down. Note that the wires that connect to PW1 and PW3 are multi-strand wires. For these, cut two inches from the end of the gray 2-conductor cable supplied in the kit. Then strip off the gray outer insulation. This will leave you with a 2-inch section each of red and black wire. After cutting all the wires to length, strip the ends back for connection to the components on the lid. Strip about half an inch for the wires that wrap around the LED legs and a quarter inch for the other wires. Note that the connection to lug 1 of the delayed flash jack will not be soldered yet, as another wire will be connected there in a later step. This connection is marked with a yellow X in Figure 84. (We'll continue to mark this connection with a yellow X in photos to follow as a reminder not to solder it until the indicated time.) Other than this connection and wires BT+ and BT- from the battery holder, all the other jumper wires are soldered. The legs of the LEDs have also been trimmed down to the solder connections.
  2. Before adding the PCB to the assembly, check the standoffs to make sure that no wires are touching the metal. The standoffs of greatest concern are the two near LEDs 1 and 4. You may wish to wrap these standoffs in electrical tape in order to avoid any potential problem later. See Figure 85.
  3. A sheet of stick-on labels is provided with your kit. You may wish to use these as aids in keeping track of the wires as you're making connections to the PCB. Figure 86 shows the labels placed on the wires.
  4. Place the PC board on the standoffs as shown in Figure 87, but don't bolt the board down yet. You'll solder all the wires first.
  5. Before starting to solder, keep the following things in mind:

    1. One way to connect the wires isin consecutive order. This may help you to keep track of where you are in the process. Another method of wiring is according to the order given on page 3 of the wiring guide. For this method, after you've done the first 3 or 4 wires, the wires will support the board.
    2. Be careful to get the right wire in the right hole, especially where the holes and labels are closely packed. See Figure 87 in which the closely-packed holes are associated with the corresponding labels by enclosing them in yellow rectangles.

Go ahead now and do the soldering. Figure 88 shows all connections soldered to the PC board, including the wires of the battery holder, which are soldered to BT+ (red) and BT- (black). Do not trim these two wires.

Figure 87.The PC board placed on the standoffs in readiness for soldering

Figure 87. Yellow rectangles associate each hole with its label

Figure 88. All connections soldered to the PC board

Figure 89. White wire connected between points labeled 1 and 2
  1. There's one wire left to solder. You should have about 6 inches of the white wire remaining. Connect it between lug 1 of the delayed flash jack and hole RV1 on the PCB. See Figure 89 for the connection points, labeled 1 and 2.
  2. As a final check before putting everything together, make sure that the legs of the LEDs are widely separated. Sometimes they get pushed together while making solder connections. Then use the remaining 4-40 bolts to bolt the PCB to the standoffs. Insert the ICs into the sockets on the PCB. It's a good idea to discharge yourself by touching a grounded pipe or even the wooden leg of a table before handling the ICs. These are static-sensitive parts. Remember the notches in the socket? Well, there's a corresponding notch in the end of the 555 and 556 timers. When you put an IC in a socket, the notches must be at the same end. Start with the 555. Place the IC on the socket and pinch the pins gently if necessary to guide them into the holes. When all the pins are aligned, push down firmly on the IC to seat the pins. Repeat with the 556 timer. The PS2501 quad optocoupler doesn't have a notch, but it does have a faint white dot which is used for orientation. Make sure that the white dot is toward the interior of the board. See Figure 90. The last IC is a single PS2501. This has 4 pins, but you'll insert it in the remaining 8-pin socket. Insert the IC in the 4 holes on the left side of the socket. In this case, orient the white dot toward to outside of board. Finally, insert the fuse into the fuse holder. You'll have to apply some force to snap the fuse into the clips.
  3. Figure 91 shows how the battery holder is positioned in the box relative to the PCB. Figure 92 shows the battery holder inside the box. A yellow rectangle has been drawn around the holder to identify it. Use the hook and tape included with the battery holder to hold it tightly to the bottom of the box.
  4. Before seating the lid on the box, check that all the wires are stowed neatly under the lid so that no wires get pinched when the lid is seated. If you're using a battery to power the box, go ahead and install it now. You may screw the box lid on now or wait until later in case you want to have quicker access to the interior. Figure 93 shows the completed box.


battery holder positoning in box
Figure 90. Seating the ICs and the fuse Figure 91. Position of the battery holder relative to the PCB Figure 92. Battery holder in place (in yellow rectangle) Figure 93. The completed control box


Testing the timing functions

Before preparing the cables to connect to the box, there are some tests you can perform to see if the box is working correctly. You'll either need to have a 9V battery installed or be using a 9V AC/DC adapter. (If you use your own adapter rather than the one provided by, be sure that it has 1A maximum rating.) You can have a battery in the box and be using an adapter at the same time. When the adapter is plugged into the box, the internal battery is automatically disconnected from the circuit.

The diagram of the timeline shown to the right may help in understanding how the timing works.

  1. When a trigger pulse is received, the 556 timer produces its first output pulse, called Output Pulse 1 in the diagram. At the same time the Start LED lights. If a flash or camera is connected to an instant output, that device will also be actuated.
  2. Output Pulse 1 remains high for a length of time determined by the settings of the Fine and Coarse Delay knobs. At the end of this time, the Start LED goes out, and the Finish LED turns on. At the same time, a flash or camera connected to a delayed output will be actuated.
  3. Output Pulse 2 remains high for a length of time determined by the setting of the Timeout knob. During this time, the Finish LED remains on, and the flash or camera cannot be activated.

Begin your tests with the switches and knobs in the following positions.

  • On-off switch in the Off position
  • Input Selector switch in the center position
  • Divide Delay switch in the ÷1 position
  • Timeout at 0.5 s
  • Fine Delay at 0
  • Coarse Delay at 500 ms (or 0.5 s)
Power test Switch on the power. The Power LED should light and remain lit.
Trigger test Press the Test button momentarily. The Start LED should light and remain lit for about half a second. Then the Finish LED will light and remain stay lit for another half second.
Coarse Delay test

Turn the Coarse Delay to 250 ms. Press the Test button. The Start LED should remain lit about half as long (250 ms) as in the previous test. Now turn the Coarse Delay to 0 and press the Test button. The Start LED should be so brief as barely to be visible.

Fine Delay test Turn the Fine Delay to 50 ms and press the Test button. The Start LED should be brighter than when the Fine Delay was 0, indicating that the delay interval increased.
Timeout test Turn the Timeout to 0 and press the Test button. The Finish LED should light only momentarily. This indicates a minimal timeout. Now turn the Timeout to 1 second. The Finish LED should remain lit for about 1 second.
Divide Delay test

Turn the Coarse Delay to 500 ms and the Timeout to 0. Press the Test button. The Start LED should remain lit for about half a second and the Finish LED only briefly. Now flip the Divide Delay switch to the ÷10 position, and press the Test button. The Start LED should flash briefly, as the delay has been divided by a factor of 10.

Test of auxiliary input While this test isn't a timing test, you should do this now before assembling the cables. Use one of the 3.5mm mono plugs. Take off the plastic jacket, and insert the plug into the auxiliary input. Then with a paper clip or other metallic object, short across the two bare terminals of the plug. This should trigger the delay circuit and make the Start and Finish LEDs flash in sequence.
Completion Return the Divide Delay swith to the ÷1 position, and turn the power off. If the box passed all the tests, you're ready to move on to preparing the cables. If not, open the box and check your solder connections to make sure you didn't overlook any. Check that the solder flowed well rather than beading and that there are no stray wires. Check that the ICs are oriented correctly and seated well.
timeline for MT3


Set the box aside and go on to preparing the cables.


Back to top



About Tools Products Activities Galleries Projects Links Contact Facebook LinkedIn flickr
copyright © 1995-2020