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 Delay Unit with Breadboard (legacy DU-BB)


Note: These instructions are for kits before v10.


Assembly instructions


The delay unit can be used with a variety of trigger input circuits to discharge a flash unit after a selectable time delay.  The assembly instructions for the delay unit are given below.  For instructions on adding trigger inputs, go to these pages:

Parts List


The following parts are included with the kit.


556 timer IC
2 400-V SCRs (EC103D)

1-MΩ potentiometer (blue knob)

1 100-Ω   (brown-black-brown)
1 1-kΩ (brown-black-red)1
1 100-kΩ (brown-black-yellow)
1 1-MΩ (brown-black-green)
4 22-kΩ (red-red-orange)

2 0.0047-µF (472 or 0047)
1 0.01-µF (103)
2 0.047-µF (473 or 047)
1 0.1-µF (104)
1 0.47-µF (cylindrical metal case)
1 10-µF (cylindrical metal case)

3-ft of 2-conductor cable
Hookup wire
9-V battery cable2


1We are now providing 2 additional 1-kΩ resistors with delay units. This is to address an issue with some Canon flash units. The use of these resistors is described in Step 5.

2A 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


bb_002.jpg (81633 bytes)
click to view

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.



Constructing the Delay Circuit


bb_003.jpg (82207 bytes)
click to view
Step 1: Adding the 556 Timer


The 556 timer is an integrated circuit (IC) with 14 pins 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 pins 1 and 14 are shown in the figure to the right. Pins 1-7 are numbered consecutively right-to-left, and pins 8-14 are numbered consecutively left-to-right. Face the notch toward the right of the breadboard so that Pins 1 and 14 are also facing to the right. Now find Row 27 and look across to where it meets Column f. Place Pin 1 there. Pin 14 should easily fit in Row 27, Column e.


Don't press the IC down until all the pins are lined up with holes. Once they're lined up, 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.

bb_004.jpg (82428 bytes) click to view

Step 2: Adding the Potentiometer


The 1-MΩ potentiometer (blue knob) allows you to adjust the time delay of your circuit.  It has three legs, two in the front and one in the rear. Place the two front legs over Rows 28 and 30 on Column j, and the rear leg over the nearest hole on the nearby positive column. The front legs should be facing the center of the breadboard, while the rear leg is facing the outside of the breadboard. Press the legs in firmly as far as they will go, but avoid bending them. (Note that in the connections to follow, the left leg will not be connected to anything else.)

bb_005.jpg (83333 bytes)
click to view
Step 3: Adding the SCRs

SCR pin diagram

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


The silicon-controlled rectifiers (SCRs) labeled EC103D are the output stages of the delay circuit. The SCRs allow you to to discharge a flash with or without a delay.  To identify the leads of the SCR, hold it as in the diagram to the right.


The two SCRs fit into consecutive rows on Column a, except for their cathodes, which should fit into the nearest available hole in the negative (blue) column. Here's what to do. Insert the gate of one SCR into Row 15 of Column a, and the anode into Row 16 just beside it. The cathode goes to the negative column. Next, insert the gate of the other SCR into Row 17, and its anode into Row 18 just beside it. Its cathode will also go to the negative column.

bb_008.jpg (85007 bytes)
click to view
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 4: Adding the Capacitors


First, gather together all the capacitors. You should have 8 total. All but two of them have round, tan heads.  The other two have cylindrical heads. These are the electrolytic capacitors, and unlike the others have polarity. Look at the cylindrical case and find the light-colored strip bearing a negative sign. The lead on the side of this strip is the negative lead, while the other lead is the positive lead.  Note that this is also the longer of the two leads.


Locate the 10-µF electrolytic capacitor, which will have 10 µF written on its case. Insert the positive lead into Row 26, Column a. The negative lead will go to the nearest hole on the nearby negative column. Now locate your 0.47-µF electrolytic capacitor. Insert the positive lead into Row 27, Column j, and insert the negative lead into Row 25 of that same column. (See this note regarding a a discrepancy between these instructions and the circuit schematic provided with the kit.)


That's it for electrolytic capacitors. Now let's do the other capacitors. Locate the two capacitors labeled "472" or "0047." These have values of 0.0047 µF. Take one and insert one end (it doesn't matter which this time) into Row 19, Column b. Insert the other end into Row 21 of that same column. For the other 472 capacitor, insert one end into Row 18 of Column i, and the other end into Row 22 of that same column.


Finally, locate the two capacitors labeled "473" or "047." These have values of 0.047 µF. Take one and insert one end into Row 25, Column g, and the other end into Row 29 of the same column. Insert one end of the next capacitor into Row 24, Column c. The other end should reach over to the nearest hole of the negative column. 


You should have two capacitors remaining.  The 0.1-µF capacitor and one of the 0.01-µF capacitors may be substituted for the 0.47-µf capacitor in order to obtain different delay ranges.  This will be discussed in Step 9.


You may wish to trim the leads of the capacitors 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.  When you add the resistors in the next step, you may wish to trim their leads also.

bb_038.jpg (2767964 bytes) click to view

Step 5: Adding the Resistors


Each resistor is marked with four bands that are a code for the value and tolerance of its resistance. You should have 8 resistors; 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, ignoring the gold band.  The gold band indicates the tolerance of the resistance value, while the other three bands indicated the value of the resistance.


There are 4 resistors with the color code red-red-orange. These each have values of 22 kΩ. Insert one end of the first into Row 15, Column d, and the other end into Row 19 of the same column. Insert one end of the second into Row 21, Column a, and the other end into Row 30 of the same column. Insert one end of the third into Row 17, Column c, and the other end into Row 22, Column c. Lastly, insert one end of the fourth into Row 22, Column g, and the other end into Row 24, Column j.


Note for users of Canon flash units 430ex and 580ex.  In order to correct a problem in using these flash units with the delay circuit, substitute a 1-kW resistor (black-brown-red) for the 22-kW resistor for the these two resistor placements:  19d to 15d and 22c to 17c.


Locate the brown-black-red resistor (1 kΩ).  Insert one end into Row 26, Column b, and the other end into Row 30 of the same column.


Locate the brown-black-green resistor (1 MΩ); insert one end into Row 18, Column j, and the other end into Row 22 of the same column.


Locate the brown-black-brown resistor (100 Ω); insert one end into Row 26, Column h, and the other end into Row 30 of the same column.


The one resistor remaining, the brown-black-yellow resistor (100 kΩ), can replace the brown-black-red resistor (1 kΩ) later if you desire a greater reset delay. This will be described in Step 9.

bb_039.jpg (2846369 bytes) click to view

Step 6: Adding the Wires


Now you'll add wires to 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, though it's better to have longer wires than ones that are too short. Note that the wires supplied with your kit won't necessarily be the same color as those in the photographs.


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 (~2 inches)

Shortest wires (1 inch or less)

End 1  End 2 End 1  End 2
Row 30, Column e positive Row 23, Column c Row 27, Column c
Row 21, Column g negative Row 27, Column d Row 30, Column d
Row 29, Column f negative Row 25, Column d Row 26, Column d
Row 24, Column i positive Row 26, Column g Row 27, Column g
Row 19, Column e Row 23, Column g
bb_040.jpg (2921782 bytes) click to view

Step 7: Adding the Battery Clip

Locate the battery clip.  Insert the red wire into the positive column and the black wire into the negative column.  Don't attach the battery yet.

bb_042.jpg (2876599 bytes)
Cable to Output 1 for quick discharge; click to view
bb_041.jpg (2881266 bytes)
Cable to Output 2 for delayed discharge; click to view

Step 8: Connecting the Output Cable


The 3 feet of 2-conductor cable may be used to connect either of the circuit's two outputs to the PC cord of a flash unit. Output 1 provides an almost immediate discharge, while Output 2 provides a delayed discharge. 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:


If using Output 1, insert the end of the red wire on your ½" end into Row 16, Column b, and the end of the black wire into the nearest hole on the negative column. If using Output 2, insert the red wire into Row 18, Column b instead.

bb_043.jpg (2929066 bytes)
A sample jumper cable from input to ground; click to view

Step 9: Testing and Operating the Delay Circuit

Important:  Before testing the circuits, double check that all components are connected in the correct locations and with the correct polarities. Some wiring mistakes can cause the 556 timer to burn out. 


In order to test your delay circuit, its input can be shorted to ground.  First, connect your flash unit to Output 1 and connect a fresh 9-V battery to the battery clip. Then take a piece of wire and insert one end into Row 18, Column h.  (We'll call this the trigger wire.) Insert the other end to the nearest hole on the negative column (ground).  The flash should discharge immediately. Now disconnect one end of the trigger wire, and connect your flash to Output 2. Connect the trigger once again. The flash should discharge, but there may be a slight delay before it goes off. Increase the delay by turning the blue potentiometer counterclockwise. Disconnect and reconnect the trigger wire to test again. The further counterclockwise that you turn the potentiometer, the more of a delay that you should notice.  Note, however, that in the furthest counterclockwise position, the circuit may not respond. If that's the case, back off a little from the maximum position.


Troubleshooting:  If the delay unit doesn't discharge the flash unit, there are a number of things to check.

  1. Make sure the battery is fresh.
  2. Check whether the polarity of the cable to your flash unit is reversed.  This can be done simply by reversing the cable connections on the breadboard.  This won't damage the circuit.
  3. Double check that the polarities of the electrolytic capacitors are correct, that all components are connected in the correct locations, and that all wires and components are firmly seated in place.
  4. Make sure the potentiometer is seated completely in the breadboard. Try pushing down on it gently while testing the circuit. If this is the problem, you may want to solder some wire legs onto the potentiometer so that the wires make secure connections with the breadboard contacts.
  5. If there were wiring mistakes, it's possible that the 556 timer is burnt out.  Contact us for a replacement 556 or check to see if your local electronics store carries the component.

Changing the delay range:  A half second delay is long for many high-speed photography situations.  You can change the range of the potentiometer by removing the 0.47-µf capacitor and replacing it with one of smaller value.  Extra 0.1-µf and 0.01-µf capacitors have been 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.


Changing the reset delay: After the flash unit discharges, it will be inactive for a short time before it can be discharged 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 actually less than the recharge time of most 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 100-kΩ resistor.  This will increase the reset delay to about a second.


If you're using a sound or photogate trigger as an input to the delay circuit, you would connect the positive output of the trigger to Row 18, Column g and the negative output of the trigger to the negative column (ground). More details are provided in the instructions for building these triggers. 


Assembly instructions for other kits



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