Hands On Physics
Assembling and Checking the Circuit
This activity continues the construction of the sun photometer.
See tools and materials for a complete
list of the parts required.
Assemble the Circuit
OK, you're almost through! Be sure to follow each of the remaining steps
carefully to avoid errors.
The batteries attach to pins 4 and 7 of the opamp through the double pole
Find these wires which you previously prepared: (8 cm red and 10 cm black
- Form a u-shaped hook in the exposed 12-15 mm end of each wire as you
did when preparing the switch.
- Loosen the end hex nuts on the two terminal posts that protrude inside
the VHS case.
- Place the u-shaped hook of the red wire over the terminal of the red
post and use pliers to tighten the nut over the wire. The bend in the hook
should be oriented in the same direction the nut is tightened (clockwise).
- Place the u-shaped hook of the black wire the terminal of the black
post as described in the previous step. Use pliers to tighten the nut over
- Notice that the holes in the breadboard are coded. Rows are designated
by letters of the alphabet. Columns are designated by numbers. This means
we can label any hole in the breadboard with a letter and a number. Install
the 741 operational amplifier integrated circuit (IC) in the breadboard
as shown in Fig. C4. Pin 1
of the 741 should be installed at position F1 in the breadboard. Gently
push down of the IC until its pins are firmly inserted in their holes. Make
sure all 8 pins are properly inserted. If a pin bends and does not install,
gently remove the IC, use pliers to straighten the pin and try again.
- Use a pencil or marker pen to mark the LED leads at points 13 mm from
the LED body.
- Notice that one side of the lower end of the LED has a flat place
as shown in Fig. C1 and Fig.
C4. Hold the leads of the LED with pliers so that the side of the pliers
away from the LED body is along the marked points on the leads. Orient the
LED so that the flat space is nearest you and bend the leads at a right
- Insert the end of the LED through the upper hole in the angle bracket
adjacent to the breadboard while also inserting its leads in holes J2 and
J3. Be sure the lead closest to the flat space on the LED is inserted in
hole J2. Press the back of the LED flush against the angle bracket.
- Insert a black connection wire between holes G3 and X1.
- Insert the 2 wire leads of the resistor in holes H2 and D3.
- Insert the red wire from the red output terminal in hole A3.
- Insert the black wire from the black output terminal in hole X5.
- Remove the outer retaining hex nut and switch plate from the switch,
align the switch so that the 2 terminals without wires face the 2 terminals
installed in the rigid side of the case, and install the switch in the hole
in the bottom of the case. Replace the hex nut (but not the switch plate)
over the switch and tighten with pliers.
- Insert the center black switch lead in hole G4.
- Insert the center red switch lead in hole B2.
- The exposed copper leads from the 9-volt battery connecter wires are
thin and by themselves will not necessarily stay inserted into holes in
the breadboard. So follow this method: Insert the black lead from a 9-volt
battery connector half way into hole E23. Then force the black lead from
the lower left side of the switch into the same hole.
- Find the red connection wire you prepared. Insert the red lead from
the same 9-volt battery connector half way into hole X19. Then force one
end of the red connection wire into the same hole. IMPORTANT: Make sure
the wire you have just installed is from the same battery connector!
- Insert the black lead from the second 9-volt battery connector half
way into hole X11. Then force the second end of the red connection wire
(the first end of which you previously inserted into hole X19) into the
same hole (X11).
- Insert the red lead from the second 9-volt battery connector half
way into hole F23. Then force the red lead from the left side of the switch
into the same hole.
Now set VHS-1 sun photometer aside and take a break before going further.
Checking the Circuitry Inside the VHS-1
It is absolutely essential that all wires and parts be installed correctly!
Otherwise, the circuitry may be damaged and the batteries may be rapidly
discharged. Therefore, use this checklist to make sure you have installed
- Look at the operational amplifier. Is pin 1 (the one nearest the slot
or mark in the case) inserted in hole F1?
- Is the lead nearest the flat space on the LED installed in hole J2?
- Is the resistor connected between holes H2 and D3?
- Is there a black "jumper" wire between holes X1 and G3?
- Does the center red switch lead go to hole B2?
- Does the center black switch lead go to hole G4?
- Is there a red "jumper" wire between holes X11 and X19?
- Do both the red lead from one 9-volt battery clip and the second red
switch lead go to hole F23?
- Does the black lead from the above battery clip go to hole X11?
- Do both the black lead from the second 9-volt battery clip and the
second black switch lead go to hole E23?
- Does the red lead from the second battery clip go to hole X19?
- Does the red output terminal lead go to hole A3?
- Does the black output terminal lead go to hole X5?
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