Description
Procedure
Teachers Guide
Purpose
Materials
Lab Hints
Time
Hazards
Precautions
Disposal
Acknowledgment
Key Words
An inexpensive device is constructed from readily available materials that permits the monitoring of the optical density of a solution. The device is constructed so as to connect directly to the game port of an Apple® IIe or Apple® IIgs computer.
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Cut two square pieces of wood 3(3 / 8)" x 3(3 / 8)" x 1(1 / 2)" from 2" x 4" boards.
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Draw diagonals to locate the centers of the blocks.
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Clamp one of the blocks in a vise. Use a (5 / 8)" paddle bit to drill a hole 0.25" deep.
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Use the photocell as a template and mark places for the wires.
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Clamp the block in a vise. Drill holes through the block at the marks using a (5 / 64)" regular drill bit.
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or Figure V120V1
Use a utility knife, wire strippers, or other suitable device to remove 8-9" of outer covering from one end of a 4-6 foot length of 24-gauge solid-copper 4-conductor phone cable.
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Strip about 0.25" of insulation from each of the four wires.
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Insert the green and yellow wires through the back of the block.
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Use a needle-nose pliers to bend the ends of the photocell wires. Bend loops into the wires.
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Hook these to the diode wires. Crimp. Solder.
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Push the photocell back into the recess.
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Clamp the second wood block in a vise. Use a (3 / 8)" paddle bit to drill a perpendicular hole 1(1 / 8)" deep into the center of the other wood block.
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Use a regular 0.25" drill bit to drill this hole through completely.
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Locate a point 0.375" from the face on the center line of one side of the block.
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Clamp the block in a vise with the marked spot up. Use a (9 / 16)" paddle bit to drill a hole about 2.75" deep at this point. This hole will hold a 13 x 100 mm test tube.
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or Figure V120V2
Seat the LED from the side of the larger hole.
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Bend the long wire lead away from the hole. Place a 5-position lug with center lug 3 over the straight wire and an adjacent lug 2 over the bent long wire. Fasten the lug in place with a screw.
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Solder both of the wires.
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Use a needle nose pliers to crimp a 0.5 watt, 33 W resistor between lugs 3 and 4. Trim excess wire. Solder the resistor in place.
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Attach the red wire to lug 2. Crimp. Solder. Attach the black wire to lug 5. Crimp. Solder in place.
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Snip off the indicated potentiometer lug.
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Attach the potentiometer between lugs 4 and 5, and solder in place.
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or Figure V120V3
Protect the lug strip with a piece of insulating tape.
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Place the two halves of the Blocktronic I together. Drill a 0.25" hole in corner.
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Fit with washer and (3 / 16)" diameter bolt that is at least 3.25" long.
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Fasten with washer and wingnut. Repeat for a diagonal corner.
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or Figure V120V4
Where Apple® IIe computers are to be used, the Doing Chemistry staff suggests connecting the end wires to a 9-pin connector. In this way the Blocktronic I may be conveniently attached to the computer, and there is no question about making correct connections. The video often shows this model in use.
Remove about 2" of outer covering from the free end of the Blocktronic cable. Strip (1 / 4)" of insulation from each of the four wires. Twist the red and yellow wires together.
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++Connecting to a Macintosh with ULI
Where a Macintosh is to be used with the ULI interface box, either connect the probe which accompanies the ULI to the wires directly or add a 5-pin DIN connector.
To connect directly, add an aligator or test clip to the orange wire of the probe. Clip the orange wire to the twisted red and yellow wires or the Blocktronic. Clip the black wire to the black wire of the blocktronic. Clip the red wire to the green wire of the blocktronic.
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Soldering the connector may prove a bit difficult, but adding the Din connector makes connection fool proof. Follow the same procedures for soldering, but the pin connections are shown in the figure. Attach wires to pins 5-Volts (red and yellow), voltage in (Vin green), and ground (black).
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++Apple II completion and calibration:
Note the numbering system for the pins.
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Lugs 2, 3, and 5 will be used. Heat these with the soldering iron, and fill them with solder. Heat lug 5. Insert the green wire into this lug while heating.
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Heat lug 3. Insert the black wire into this lug while heating. Twist the red and yellow leads. Heat lug 2. Insert the twisted red and yellow wires into this lug while heating.
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Insert the connector into the bottom half of the hood shell.
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Cover with the top half of the hood.
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Fasten the retaining screws in place.
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Fasten the set screw to hold the cable in place.
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Attach the Blocktronic I through the 9-pin connector to the back of an Apple® IIe computer.
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Turn on the computer.
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Check that a green light is visible in the tube. If the LED does not light up, check the connections for the black and red wires. Check the solder connections on the lug. If these seem correct, rotate the potentiometer dial.
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Turn off the computer. Insert the appropriate floppy disc into Drive A of the computer. Turn on the computer and monitor. A title screen will appear. Follow the instructions at the bottom of the screen.
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Select the GENERAL LABORATORY INTERFACING program.
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Select the option, GAME PORT STATUS.
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When using a 9-pin connector, the instructions for the adapter box should be disregarded. Press return.
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The green LED should light. If the LED does not light up, repeat the checkout procedure that was described earlier. Check the connections for the black and red wires. Check the solder connections on the lug. If these seem correct, turn the potentiometer dial around.
The reading or "Paddle Value" for GC0 should be less than 255. If the value is 255, check the green and yellow wires for breaks. Loosen the wingnuts and move the blocks so as to minimize the reading. Fasten the wingnuts for a position of the blocks that gives a minimum reading. Adjust the potentiometer so that the reading at GC0 is about 50. Adjusting the potentiometer to a reading lower than 50 may result in the LED burning out.
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At this point the Blocktronic I is ready for use.
++Macintosh calibration:
Connect the blocktronic. Turn on the computer. Turn on the ULI interface. Load the "Data Logger" Software.
Check to be sure the LED in the blocktronic is on. Adjust the light level to fairly bright with the potentiometer. Block the light path.
Select "Calibrate" from the "Collect" menu. Block the light path with several folds of paper. When the reading stablizes, click "OK," and type 1.5 for the "real world reading." Remove the paper, and insert a test tube with the blank solution (water for many of these experiments). When the reading stablizes, click "OK," and type 0 for the "real world reading."
Save the calibration file with the "File" menu item, Save Calibration.
To assemble and test a Blocktronic I interface for colorimetry experiments.
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Apple® IIe, Apple® IIc, or Apple® IIgs computer
Appropriate SERAPHIM Software
1 green subminiature LED indicator lamp (RS 276-069)
1 33 W, 0.5 watt 10% resistor (RS 271-007)
1 5-lug terminal strip (RS 274-688)
4-6' 24-gauge solid-copper 4-conductor phone cable (RS 278-1320)
small amount 0.032 light duty rosin core solder (RS 64-005)
2 squares of 2" x 4" wood (1.5" x 3.5" x 3.5")
1 roll electrician's tape
1 short wood screw
2 (3 / 16)" diameter bolts, 3.25" long, with washers and wingnuts
Apple connector
1 9-pin D-subminiature connector (RS 276-1537)
1 9-pin D-subminiature hood (RS 276-1538)
or
ULI Mac connector
5-pin DIN connector(RS274-003A)
1 photoconductive cell, CdS (3-20K ohm light: 500K ohm dark) (338-76C-348)
1 500 ohm 0.25 watt trimmer (Potentiometer 320-1510-500)
Both photocell and potentiometer are available from:
Mouser Electronics
2401 Highway 287 N
Mansfield, TX 76063-4827
800 633-2246
Tools:
wood saw
power drill, set of drill bits (0.25", (5 /64)", 0.5")
0.375" paddle bit; 0.625" paddle bit
soldering pencil
vise to hold wood
pencil
needle nose pliers
straight edge
The numbers for the materials labeled RS (e.g., RS xxx-xxx) are Radio Shack® catalog designations. Most of the recommended parts may also be obtained from other suppliers.
Although you may have students build the Blocktronic I during class time, preassembly of this part is recommended.
Make sure the "paddle readings" are above 50 to prevent excessive loss of the LEDs.
Macintosh users may wish to use the colorimeter probe available from Vernier Software with a ULI or serial box interface. Or, you may adapt the blocktronic to the ULI interface box by connecting the generic ULI probe to the wire ends or substituting a 5-pin DIN plug on the blocktronic.
The assembly time is 30-90 minutes depending upon experience with the tools and techniques.
The check out procedure takes 5 minutes. Installing the adapter box takes 5-15 minutes.
Cuts and burns during assembly are possible.
Do not touch hot soldering irons.
Handle saws and power drills cautiously. Be careful about loose garments near the drill.
Waste materials produced during the assembly of the Blocktronic may be disposed of safely with ordinary solid wastes.
The original module was written for Project SERAPHIM by Thomas Adams, Kenneth Hartman, David Journeay, Paula Miles, and John W. Moore.
Project SERAPHIM is supported by the National Science Foundation.
For additional information write:
Project SERAPHIM
Department of Chemistry
University of Wisconsin-Madison
1101 University Avenue Madison, WI 53706
Blocktronic assembly
computer interfacing
colorimeter