*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. For soldering, you'll need a 15-30 W soldering iron and resin-core solder.

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.

The metal plate included with the breadboard isn't needed for the assembly instructions below.

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..

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.

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.

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.

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.

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.

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.

Step 8: Connecting the Output Cable to Your Flash Unit

The 3 feet of 2-conductor cable may be used to connect either of the circuit's two outputs to a flash unit.*

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 that the photographs show a delay unit already built on the right side of the board.  The photogate may be used with or without the delay unit. However, the 9-V battery cable is required for the operation of either kit.  This is the cable coming in from the left with the red and black leads above and below the 555 timer IC.  The column of 25 holes to which the red wire is connected will be termed the positive column, while the column to which the black wire is connected will be termed the negative column.  While wiring the circuit, be sure to have the battery disconnected from the battery cable.

Step 1: Adding the 555 Timer

The 555 timer is an 8-pin IC. There is a semicircular notch that can be used to identify the pins.  See the diagram to the right. Orient the IC so that the notch faces the left side of the breadboard. Now find Row 2 and look across to where it meets Column E. Place Pin 1 there. Pin 8 should easily fit into 2F. Press the IC firmly down in place; again, it should be seated across the center division of the breadboard.

Step 2: Adding the Potentiometer

The 10-kΩ potentiometer (white knob) allows you to adjust the sensitivity of your photogate. It has three legs, two in the front and one in the rear. Place the two front legs over 9F and 11F, and the rear leg into 10J. The front legs should be facing the center of the breadboard, while the rear leg faces the outside of the breadboard. Press the legs in firmly as far as they will go.

If the legs won't stay seated in the breadboard, a tip is to bend all three legs slightly outward away from the potentiometer. Then insert the legs. The slight outward bend will help the potentiometer stay seated.

Step 3: 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 timer and potentiometer, 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.

Note this error in the photo: The wire from 4H to 6E is not needed, although it has no effect on the circuit if included.

*This wire is only needed if you're connecting the photogate to a delay unit.

Step 4: Adding the SCR and red LED

The silicon-controlled rectifier is the output of the photogate circuit and is connected to the input of the delay circuit.  Putting in this SCR is easy since all three leads go in consecutive rows along Column B. Put the cathode into 8B, the gate into 9B, and the anode into 10B.

The red LED can be used to check for correct operation of the circuit even without a flash unit connected. It has legs of different lengths to help indicate the proper polarity. Insert the short leg into 8J, and the long leg into the (+) column. You may wish to trim these leads so the LED sits closer to the breadboard; however, be sure to trim the short leg shorter than the long leg so you can connect the LED with the right polarity later.

Step 5: Adding the Resistors

Locate the brown-black-brown resistor (100 Ω), and place it between 4-9D.

There are two yellow-violet-brown (470 Ω) resistors.  Insert one end of the first into 1F; the other end should reach over to the nearest hole in the (-) column. The second resistor connects between 3-8H.

You may wish to trim the leads of the resistors so 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 capacitor in the next step, you may wish to trim its leads also.

Step 6: Adding the Capacitor

Locate the capacitor labeled 103, which has a value of 0.01 µF. Place it between 5-7J.

Step 7a: Preparing and Connecting the Photogate Cable

Select your kit model below for instructions on how to assemble the photogate cable. Return here after you've assembled the cable.

SPG1

SPG2

Now, connect the free ends of the 3-conductor cable to these holes on your breadboard:

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

Step 7b. Connecting a Flash Unit

The three feet of 2-conductor cable may be used to connect the output of the circuit to a flash unit.* If you have assembled a delay circuit, you will have already prepared the output cable from those instructions. If not, see the information in the yellow box.

To connect the output cable from the flash to your circuit, three different connections are possible if you're using a delay unit and one connection if you're not. Note that for the delay unit outputs, a jumper wire must be added from the output of the trigger 10E to the input of the delay unit 18F. When using the trigger without the delay unit, be sure to disconnect this latter wire, as some flash units can burn out the 556 timer if connected to the timer input.

Step 8: Testing and Operating the Circuit

If you're using the individual PT and IR LED components, lay them down on a table a few inches apart pointing at each other.  You may want to tape down the cables so that the components can't shift positions.  If you're using an interrupter, the components are already fixed in position.

With a 9-V battery connected to the battery clip and your flash unit connected to one of the outputs as described in step 7b, you can now test your circuit.  The red LED of the photogate should be lit if the PT and IR LED are aligned correctly. Run your finger between the PT and IR LED in order to break the photogate beam.  The red LED should go out momentarily. If your flash cable is connected directly to the photogate or to Output 1, you should notice an immediate discharge of your flash unit.  If your flash cable is connected to Output 2, you may notice a short delay before discharge, depending on the setting of  your delay circuit.  If your flash unit doesn't discharge, you may need to adjust the sensitivity of the photogate.

Adjusting the sensitivity: First make sure the photogate is working. Then turn the white knob counterclockwise until the photogate indicator LED goes off. Then back off the knob a little bit until the LED comes back on.

If you change the distance between the PT and IR LED (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 8 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.