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Assembly and Operating Instructions for Kits


Instructions for Building the Photo Gate 2i (PG2i)


Assembly instructions for other kits


Photo Gate 28 Photo Gate 28
Control side Sensor side




For individual photos of the parts supplied in the kit, see the Parts List.


If you would like to refer to a circuit schematic while you work, download one here.


In these instructions, click on any image for a larger view. (In order to open the image in a new tab or window, right click and select open in new tab or window.)



Tools that you'll need


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

  1. 15-30 W soldering iron and solder
  2. Wire stripper (photo below)

  3. A small diagonal cutter (photo below) makes it easy to trim stray wires, but other kinds of snipping tools such as scissors may work.

  4. Needle-nose pliers (photo below) make it easier to handle wires, especially if you have big fingers.

  5. A magnifying glass is useful to inspect solder joints.

  6. A lighter or matches to shrink heat-shrink tubing, if the project requires it. (The PG2i kit does not require this.)

  7. A drill motor and these drill bit sizes: 3/32, 1/8, 1/4, 3/8 in

  8. A small, flat wood or metal file
  9. Rubber or contact cement to affix the label to the project box lid

  10. Hammer and a pointed instrument such as a large needle or a punch
  11. Stencil or razor knife and a straightedge
  12. Hole punch such as that used for punching paper for binders
  13. Mild solvent such as denatured or rubbing alcohol and soft, clean cloth
Wire strippers diagonal cutter needle-nose pliers
Wire stripper Diagonal cutter Needle-nose pliers


Be sure to 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.


Soldering Components to the PCB

About the printed circuit board (PCB)


Note the photos of the PCB below. In the instructions, we'll use the terms top side and under side to refer to the two sides of the PCB. This will be important, as some components are mounted on the top side and soldered to the underside, while one component (the interrupter) is mounted on the under side and soldered to the top side.

Top side of the PCB Under side of the PCB


Step 1. Adding the 8-pin socket to the PCB


Photo 1a: Orient the 8-pin socket on the PCB as shown. Note the notch at the top.


Photo 1b: On the under side of the PCB, crimp the 8 pins to the side to hold the socket in place.


Photo 1c: Solder the pins, being careful not to bridge solder between the pins.


Photo 1a Photo 1b Photo 1c


Step 2. Adding the resistors to the PCB


Photo 2a:470-ohm resistor Start with the PCB and one of the 470 Ω resistors (see photo to the right). The resistance value is indicated by the sequence of band colors. Yellow-violet-brown indicates a 470 Ω resistor (yellow = 4, violet = 7, brown = 0). Insert the legs of the resistor into the location labeled R1 on the PCB. Note that the resistors aren't polar and can be placed in either of the two possible orientations.


Photo 2b: Solder the legs to the back side of the PCB and then clip off the excess. The completed solder connections, circled in yellow, are shown in the photo.


Photo 2c: There are 3 remaining resistors. Solder these as follows: 1k (brown-black-red) into positions R2 and R3, the other 470 into position R4.


Photo 2a Photo 2b Photo 2c


Step 3. Adding the variable resistor, capacitor, and SCR to the PCB


Photo 3a: The variable resistor (also called a potentiometer) has a white knob and three legs. Insert the legs into the location for RV1 on the PCB and solder into place on the under side.


Photo 3b: Position the capacitor on the PCB as shown in the photo. Solder the legs on the under side of the board.


Photo 3c: Position the SCR as shown, making sure that the flat side of the component aligns with outline on the PCB. Push the SCR down to seat the legs. Then solder on the under side of the board. Solder quickly, as the SCR may be damaged by overheating. If you find yourself taking too long, simply let the SCR cool for a while and then go back to work.


Photo 3d: The photo shows all the components except for the interrupter soldered to the board. Make sure the variable resistor is turned to the position shown. This is the midway position and works fine for nearly all situations.


Photo 3a Photo 3b Photo 3c Photo 3d


Step 4. Adding the interrupter to the PCB


interrupter graphicA diagram of the interrupter is shown to the right. Refer to this in order to orient the component correctly on the PCB.


Photo 4a: Turn the PCB over so that you're looking at the underside. Note the 4 numbered holes. These correspond to the numbers on the diagram to the right. Place the interrupter beside the holes in the same orientation in preparation for soldering.


Photo 4b: Insert the 4 legs of the interrupter into the board and solder on the top side of the board.


Photo 4c: A view from the side of the soldered interrupter is shown.


Photo 4d: Insert the PS2501-2 optocoupler into the 8-pin socket with the notch in the optocoupler at the same end as the notch in the socket. When seating the optocoupler, make sure to feed all eight pins into the holes. Then push down to seat the component securely.

Photo 4a Photo 4b Photo 4c Photo 4d


Preparing the Project Box

Step 5. Drilling the lid and the bottom of the box


Photo 5a: There are 4 templates, one for the lid, and the other three for the bottom and sides of the box. Cut out the 4 templates. Then select the template for the box lid. Place the template in the under side of the project box lid. Using a hammer and a sharp, pointed instrument such as a large needle or a punch, mark the centers of the 7 holes on the template.


Photo 5b: Remove the template. Drill 3/32-in starter holes at each of the 7 locations that you marked. Then drill the holes to the sizes as marked on the drilling template.


Photo 5c: Select the template for the bottom of the box and set in place. Use your needle or punch to mark the centers fo the three holes.


Photo 5d: Remove the template and drill the three holes using the previous technique.

Photo 5a Photo 5b Photo 5c Photo 5d


Step 6. Drilling the sides of the box


Photo 6a: Select the template for the long side of the box. Tape it onto the box as shown in the photo. Note the location where the side hole will be compared to the holes in the bottom.


Photo 6b: Mark the center of the 1/8-in hole, remove the template, and drill the hole.


Photo 6c: Select the template for the short side of the box. Tape it onto the box as shown in the photo. Again, note the location where the side hole will be compared to the holes in the bottom.


Photo 6d: Mark the center of the 1/4-in hole and remove the template. Drill a starter hole and then drill the 1/4-in hole.

Photo 6a Photo 6b Photo 6c Photo 6d


Step 7. Completing the box


Photo 7a: Note in the photo how the two 3/8-in holes have been joined into an oval. While it's not essential to do this, it may help for seating the interrupter well. In order to join the holes, here's one technique: a) drill a 3rd 3/8-in hole between the other two, b) Use a sharp knife to cut away the excess plastic. The plastic is soft enough to be cut with a sharp knife, c) use a file to complete the oval.


Photo 7b: Remove the nut and the tab from the RCA jack. Slip the body of the jack through the 1/4-in hole in the short side of the box. Slip the tab over the threads inside the box and then screw on the nut.

Photo 7a Photo 7b


Step 8. Adding the label


Photo 8a: Trim around the black border of the lid label. A stencil or razor knife with a straightedge will help to get straight cuts, but sharp scissors will also serve.


Photo 8b: Pull the backing off one of the laminate sheets, and lay the sheet, sticky side up, on a table. Carefully place the lid label, label side down, onto the sticky side of the laminate sheet. In order to avoid getting air bubbles, apply the shorter edge of the label first and gradually push it down onto the laminate with a finger.


Photo 8c: Remove the backing from the other laminate sheet and carefully apply it, sticky side down, to create a sandwich of the two laminate sheets with the label in the middle. Use the technique described above to avoid getting air bubbles. When the laminate is in place, rub a finger over the laminate and around the edges of the label to ensure a good seal. Finally, use a stencil or razor knife or sharp scissors to trim the excess laminate from around the label. The completed label with laminate applied and trimmed is shown in Photo 8c.


Photo 8d: Use a hole punch to punch out the two 1/4-in holes on the label. If you don't have a hole punch, the point of a sharp knife can be used to carve out the holes. Ragged edges will be covered later when the components are mounted.


Photo 8e: Cut the 2-in section of plastic tubing into two 1-in pieces. Align the label with the two 1/4-in holes in the top of the lid of the project box. Then push the two pieces of tubing through the holes to force alignment. Next, use a small screwdriver or a sharpened pencil to push through the 1/8-in hole in the lower right corner.


Photo 8f: Now it's time to glue the label to the top of the lid. First remove the plastic tubing and label from the lid. Then use rubber cement or other repositionable adhesive for this. Spread the adhesive over both the lid and the under side of the label (not shown). Put the label in position on the lid and use the plastic tubing and the point of a pencil or screwdriver as before to make sure that the holes are aligned. Flatten the label by rubbing a finger over it and hold in position for a minute or so to insure adhesion. Then carefully remove the plastic tubing to avoid shifting the position of the label. Any glue that extends beyond the edge of the label can be rubbed off with a finger. If there is glue smeared on the label that can't be rubbed off, use a mild solvent such as denatured or rubbing alcohol and a soft, clean cloth to clean the label. Finally, place the label under a stack of books or other weight to press it for a few hours. When completed, the lid with label should look like Photo 8f. Check the under side to see if portions of the label overlap the two 1/4-in holes. If so, use a stencil knife, razor, or knife blade to trim the label back to the boundaries of the hole. This will make it easier to insert components later.


Photo 8g: Push through the three remaining 1/8-in holes in readiness to insert the bolts.

Photo 8a Photo 8b Photo 8c Photo 8d
Photo 8e Photo 8f Photo 8g  


Adding Components to the Lid of the Project Box

Step 9. Adding the standoffs, switch, and LED


Photo 9a. Insert the 4 bolts through the top of the lid. Then screw the 4 standoffs to the protruding bolts on the under side of the lid.


Photos 9b,c: In Photo 9b showing the switch, notice the ring with the tab pointing toward the base of the switch. When you mount the switch on the lid of the project box, point the tab the opposite direction. Then when you insert the switch through the 1/4-in hole on the under side of the lid, the tab will slip into the 3/32-in hole, serving to prevent the switch from turning. See Photo 9c showing the switch mounted from below with the tab inserted in its hole. Now place the washer and nut on the switch on the upper side of the lid and tighen. The completed assembly is shown in Photo 9d from the upper side.


LED holder

Photos 9e-g: The LED holder has two parts shown to the right. The first step in mounting the LED is to snap the collar of the LED holder into the hole from the upper side of the lid. See Photo 9e. From the under side of the lid, insert the LED into the collar as shown in Photo 9f. Note that one leg of the LED is longer than the other. Orient the LED so that the longer leg is the one nearer to the switch. Now you'll need to push the LED into the collar until the LED snaps into place. This may require quite a bit of force, depending on how tight the fit is. You can use a small, blunt instrument to push on the base of the LED until you hear it snap into place. The final part of the LED assembly is to place the ring over the collar on the under side and push it into place. When the LED is correctly seated, it will appear from the side as shown in Photo 9g.

Photo 9a Photo 9b Photo 9c Photo 9d
Photo 9e Photo 9f Photo 9g  


Wiring the Project Box to the PCB

Step 10. Wiring the box to the PCB


Photo 10a: Place the PCB onto the standoffs as shown and bolt in place.


Photos 10b,c: In order to connect wires to the legs of the LED, first strip the wires back half an inch on one end. Do this for the 2-in lengths of red and blue wire. Wrap the stripped end around a brad or small nail as shown in Photo 10b. Then you can slip out the nail and slip the spiral wrap over the leg. Place the red wire on the longer leg of the LED and the blue wire on the shorter leg as shown in Photo 10c. When you solder these connections, solder near the base of the LED and snip off the protruding legs. This minimizes the chances that the legs will touch each other when assembling the box.


Photo 10d: Strip the blue and red wires back about an eighth of an inch on the free ends. Then, bringing the stripped ends up from below, solder them into PCB holes E (red) and F (blue). Next, cut the white wire into two equal lengths of 2 inches. Strip back one end of each wire 1/4 inch. Then solder both of these stripped ends to the bottom lug of the switch as shown in Photo 10d.


Photos 10e,f: Strip the white wire from the switch 1/8 inch on the free end and solder into hole D on the PCB as shown in Photo 10e. Then strip the yellow wire back 1/8th inch on one end and solder it into hole C. Next, place the bottom of the box next to the lid as shown in Photo 10f. Strip the free end of the yellow wire 1/4 inch and solder to the center lug of the RCA jack. Finally, strip the free end of the remaining white wire 1/4 inch and solder to the side lug of the RCA jack.

Photo 10a Photo 10b Photo 10c
Photo 10d Photo 10e Photo 10f


Wiring the Battery Holder and Completing the Assembly

Step 11. Wiring the battery holder


Photo 11a: Slip the red and black wires of the battery holder through the 1/8th-in hole on the side of the box as shown in Photo 11a.


Photos 11b,c: Strip the red wire 1/8th inch on the free end and solder it into hole A of the PCB. Strip the black wire back 1/4 inch and solder it to the center lug of the switch. Now you can stick the battery holder to the side of the box by using the two pieces of hook and loop tape. See Photo 11b. Photo 11c shows a different view.

Photo 11a Photo 11b Photo 11c


Step 12. Completing the assembly


Photos 12a-c: Bring the lid over the box in readiness for final assembly. As you put the lid in place, feed the interrupter through the hole in the bottom of the box. Make sure not to pinch any wires between the lid and body of the box. Use the 4 black screws provided with the box to screw the lid in place. Three views of the final assembly are shown below.

Photo 12a Photo 12b Photo 12c


This completes the construction of the Photo Gate 2i. Go on to operation.


Assembly instructions for other kits




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