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Assembly and Operating Instructions for Kits


Assembly Instructions for the Delay Unit with Breadboard (DU-BB)


Note: These instructions are for v10 kits.


Assembly instructions for other kits


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. 


Parts List

The following parts are included with the DU-BB kit.


556 timer IC
2 400-V SCRs (EC103D)


1-MΩ potentiometer (blue knob)

1-100 kΩ potentiometer (brown knob)


3 100-Ω   (brown-black-brown)

1 470-Ω (yellow-violet-brown)
1 1-kΩ (brown-black-red)
1 100-kΩ (brown-black-yellow)
1 1-MΩ (brown-black-green)
2 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
3 6"-pieces of hookup wire
9-V battery cable*




*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 Delay Circuit


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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 28 and look across to where it meets Column F. Place Pin 1 there. Pin 14 should easily fit in 28E..


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.


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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 556 timer, 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. Note that the wires supplied with your kit won't necessarily be the same color as those in the photograph.


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


29E to (+) 29F to (-) 20E to 24G 28-29D
25J to (+) 15A to (-) 24-29A 27-28G
22G to (-) 11A to (-) 26-27D 28J to blue-lined column adjacent to (+) column


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Step 3: Adding the Potentiometers


The delay unit comes with two potentiometers to provide a means for coarse and fine adjustment of the delay time.


First, find the blue 1 MΩ potentiometer, which will be used for coarse delay adjustment. Place the two front legs over 19J and 21J, and the rear leg over the nearest hole on the nearby (+) 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 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 14I and 16I, and the rear leg over the nearest hole in the blue-lined column directly adjacent to the (+) column.


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Step 4: Adding the SCRs and Red LED

  SCR pin diagram

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


The output stages of the delay circuit are two silicon-controlled rectifiers (SCRs) labeled EC103D. The SCRs 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.


Both SCRs will go into Column B. Insert the cathode of one SCR into 11B, the gate into 12B, and the anode into 13B. Similarly for the second SCR, insert its cathode into 15B, gate into 16B, and anode into 17B.


The red LED will be used to check for correct operation of the circuit even without a flash unit connected. Insert the short leg of the LED into the (-) row, beside Row 22, and its long leg into the nearest hole in the red-lined column directly adjacent to it.


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Step 5: Adding the Resistors


There are 8 resistors that will go into the delay unit. 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.


There are 3 resistors with the color code brown-black-brown. These each have values of 100 Ω. Place one resistor between 12-20D, the second between 16-23C, and the third between 14-19G.


There are 2 resistors with the color code red-red-orange. These each have values of 22 kΩ. The first resistor goes between 22-29B; the second will go between 23G and 25I.


Locate the brown-black-red resistor (1 kΩ), and place it between 26-29C.


Locate the brown-black-green resistor (1 MΩ), and place it between 18-23I.


Locate the yellow-violet-brown resistor (470Ω); insert one end into 23A, and the other end into the nearest hole in the red-lined column adjacent to the (-) column.


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.


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


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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 6: Adding the Capacitors


First, gather together all the capacitors. There are 6 that will go into the delay unit; all but two of these have round, tan heads.  The other have cylindrical heads. These are the electrolytic capacitors, and unlike the others they have polarity. 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 27A. The negative lead will go to the nearest hole on the nearby (-) column. Now locate your 0.47-µF electrolytic capacitor. Insert the positive lead into 28H, and the negative lead into 29G.


Locate the two capacitors labeled "472" or "0047" or "00472Z". These have values of 0.0047 µF. Take one and insert one end (it doesn't matter which this time) into 20A. The other end will go into 22A. Place the other 472 capacitor between 18-23H.


Finally, locate the two capacitors labeled "473" or "047." These have values of 0.047 µF. Take one and place it between 22-26J. Insert one end of the next capacitor into 25A; its other end should reach over to the nearest hole of the (-) column.  You should have two capacitors remaining.  These may be substituted for the 0.47-µf capacitor in order to obtain different delay ranges.  This will be discussed in Step 9.


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Step 7: Adding the Battery Clip


Locate the battery clip.  At the left end of the breadboard, insert the red wire into the positive column and the black wire into the negative column.  Don't attach the battery yet.

Note that you can also power the circuit with an AC-to-DC adapter having a 9-V output such as the one shown here.

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Cable to Output 1 for immediate discharge of a flash unit; click to view

Step 8: Connecting an Output Cable to Your Flash Unit


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. (For quick reference, select a link: PC or FA kit / VPC kit.)


Once you've prepared the trigger cable, connect the wires to the breadboard according to this table.


Note that trigger circuits can also be connected to a camera shutter or wireless transmitter. See this page for more information.


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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 18F.  (We'll call this the trigger wire.) Insert the other end to the nearest hole on the negative column (ground).  The red LED should light momentarily, and 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 the LED lights and the flash goes off. Increase the delay by turning the blue potentiometer counterclockwise. Disconnect and reconnect the trigger wire to test again. If you're unable to get the red LED to light or the flash unit to discharge, see the Troubleshooting section below.


Making fine and coarse delay adjustments: The two potentiometers are used as variable resistors. The blue 1-MΩ potentiometer provides coarse delay adjustment, while the brown 100-kΩ potentiometer provides a finer adjustment. Once your delay has been set 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 that you should notice.


Changing the delay range:  A half second delay is long for many high-speed photography situations.  You can change the range of the potentiometers by removing the 0.47-µf capacitor and replacing it with one of smaller value (which yields shorter delays).  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 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 or timeout.  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 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.


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.


Troubleshooting:  If the red LED doesn't light or your flash unit doesn't fire, 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 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 your flash unit is in TTL mode, change it to A (automatic) or M (manual) with the lowest flash power that your flash unit provides.
  6. If there were wiring mistakes, it's possible that the 556 timer is burnt out.  In that case, check to see if your local electronics store carries the component, or contact us for a replacement 556.


Note on connecting a trigger input to the delay unit: 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.




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