The components

The mystery circuit consists of the following components:

1 × 8-pin IC, labelled MCP6002
1 × 14-pin IC, labelled "74xxx00"
2 × 3-pin transistors, labelled 2N3904
1 × red LED, longer lead is +ve (anode)
1 × 10uF polarized capacitor, note "+" and "-"
1 × 270 Ω, 0.25W resistor
5 × 4.7 kΩ, 0.25W resistors
2 × 22 kΩ, 0.25W resistors
a breadboard and variety of breadboard jumper wires

To view how the groups of holes are electrically connected, flip the breadboard upside down.
Begin the circuit assembly by placing a three-pin header into the breadboard, as shown. This spacer is used to support the USB power module that you will install.

Breadboard power supply

Power is supplied to the top breadboard by a USB module. A USB cable connects the module to a USB port or a USB-AC adapter.

The USB module can supply 1A of direct current at 5V to the breadboard. The red (+) rows of holes have a potential difference of V₊=+5V, relative to the blue (-) rows of holes, the ground reference (GND) at V_-=0V. Avoid 'shorting' these nodes; this may damage the module asd/or breadboard. More info on the power module can be found here.

Check that the pins protruding from the bottom of the module are not bent. Straighten them with needlenose pliers if necessary.
Align the USB module with the edge of the the breadboard, as shown, then gently press down to seat the module.

Breadboard power connections

Connect the USB module to a USB port. The LED on the USB module should light. If not, press the on/off button. If the module LED is still off, then you do not have USB power.

On some breadboards, the power and ground rails are disconnected at the middle of the breadboard. To propagate power the full length of the board, connect the two halves using four yellow jumpers, as shown.

Later, you can use jumpers to bring power to the power rows on the lower breadboard, as necessary.

Assembling a mystery circuit

You will now assemble and test a mystery circuit. Note that the numbering sequence on your bredboard may differ from that shown in the pictures. Follow these hints when assembling a breadboard circuit:

be sure that the USB power supply is OFF;
to avoid short circuits, shape and shorten leads (wires) so that components fit close to the breadboard with some 6-8mm of lead, the approximate length of a resistor, extending into a hole;
if the lead resists insertion, use the pliers to hold the lead near the end, then gently push the end straight into the hole. Complete the insertion using your finger;
to ease troubleshooting, observe the component and connection placement shown in the pictures.

Assemble voltage divider

The first step is to assemble a voltage divider circuit, adding from top to bottom, three resistors R1, R2 and R3, all of nominal 4700-Ω resistance between the +5V power supply rail and the ground (0V) rail. Recall that the five pins of a column are internally connected.

Measure each reistor with the component tester to verify the correct value. Tabulate the measured value.
Connect resistor R1 to the +5V power supply rail (red) at the top of the breadboard and the upper 5-pin column.
Connect resistor R3 to the 0V power ground rail (blue) and the lower 5-pin column.
Insert resistor R2 to connect the upper and lower columns and complete the voltage divider circuit.

Assemble an RC circuit

Follow the previously outlined steps as you assemble a series RC circuit consisting of two resistors, R4 and R5, in series with a capacitor C, connected between the +5V power supply rail and the ground (0V) rail, as shown.

Connect the 10-μF capacitor C to the ground rail (blue) and the lower pin matrix. Note the polarity of the leads!
Connect the 22-kΩ resistor R4 to the +5V rail.
Connect the 22-kΩ resistor R5 to complete the connection between C and R4.

As you assemble your mystery circuit, start creating a schematic diagram in your lab book. You can duplicate the component placement on the breadboard. Label each component and include the electrical connections hidden below the holes.

Add a transistor and associated components

The black components with three legs are transistors. Note that they have a flat side, where the part number is usually found, that allows them to be oriented in a specific way.

Select a transistor with part number 2N3904. Lets refer to this part as Q1.

Insert the transistor, as shown, with the right leg between R4 and R5.
Connect the left leg to the ground rail.
Connect a 4700-Ω resistor R6 to the middle leg, as shown.

Add the 8-pin chip

The 8-pin "chip" labelled "MCP6002" is an integrated circuit (IC). We will refer to this component as IC1.

IC pin numbers increase counter-clockwise when viewed from the top, with pin 1 identified by a dot at one corner of the chip and/or by a notch at same end of the chip.

Check that the pins are at right-angle to the chip.
Orient IC1 as shown, with pin 1 top right.
Carefully align IC1 with the breadboard holes, making sure that none of the pins are bent.
Gently press down to insert the chip into the breadboard.

Connect the 8-pin chip to power rails

Connect IC1 pin 4 to the ground rail.
Connect IC1 pin 8 to the +5 V rail.

Complete 8-pin chip connections

The 8-pin chip IC1 is next connected to the voltage divider and RC circuit. Select jumpers of the appropriate size to make these connections.

Note that, in your kit, jumpers of specific lengths may have different colours from those shown in the picture.

Connect pin 2 between R5 and C.
Connect pin 3 between R1 and R2.
Connect pin 5 between R5 and C.
Connect pin 6 between R2 and R3.

Add the 14-pin IC

The 14-pin "chip" is also an integrated circuit. Lets refer to this part as IC2.

The pin numbering scheme is the same as for the 8-pin chip and also applies to any other integrated circuits that you may encounter.

Carefully align IC2, making sure that none of the pins are bent. Note the orientation (a dot at pin 1).
Gently insert the chip into the breadboard.

Connect the 14-pin IC to power rails

Connect pin 7 to the ground rail.
Connect pin 14 to the +5 V rail.
Connect pins 9, 10, 12 and 13 to the ground rail.

Complete the 14-pin IC connections

The 14-pin chip can now be connected to the rest of the circuit

Connect together pins 2 and 6 of IC2.
Connect together pins 3 and 5 of IC2.
Connect pin 1 of IC2 to pin 1 of IC1.
Connect pin 4 of IC2 to pin 7 of IC1.
Connect pin 5 of IC2 to the open end of R6.

The assembly of your mystery circuit is now complete.

Carefully review your breadboard circuit and verify that every connection and part placement matches the layout of the accompanying picture.

Assemble a logic probe

In the next couple of steps, you will assemble and test a logic probe. With it you can test whether a pin or other circuit node has a high or low voltage applied to it.

The red component is a light-emitting diode (LED). The longer leg is the anode (+), the other is the cathode (-). We'll refer to it as LED1.

Always use a 270-Ω resistor R8 in series, otherwise excessive current will burn out the LED.

Begin by installing R8, as shown.
Connect the longer leg of LED1 to the +5V power rail.
Connect the shorter leg, on the notched side of the LED body, to R8.

Test the LED polarity

It is a good idea to check that the LED is not installed incorrectly or possibly burned out. You will need to apply power to the breadboard first.

When the USB module LED glows, the USB voltage is present on the breadboard (+) rails.
Connect R8 to GND with a jumper, as shown. LED1 should light. If not, switch the LED1 lead connections. Still no luck? Replace LED1.
Try using the jumper to check for voltage at other points in the circuit, such as the IC1 and IC2 power pins.

Add a logic probe transistor

The LED1 can be controlled with a 2N3904 transistor Q2, by varying the voltage at the base pin.

Insert Q2 as shown, with the right leg connected to R8.
Connect the left leg of Q2 to the ground rail.
Connect a 4700-Ω resistor R7 to the middle leg of Q2, as shown.

To test the transistor, the USB module should be on.

Use a jumper wire like the red one shown to connect the open end of R7 to +5V. LED1 should light.
With the jumper disconnected or when connected to 0V, the LED should be off.

Test the nystery circuit

To test your mystery circuit, check that the USB module is on, then connect the probe to pin 6 of IC2.

When the USB module LED is lit, your circuit LED1 should blink on/off a couple of times per second.

If yes, congratulations! You have breadboarded a working mystery circuit. If your circuit does not seem to do anything, there is an electrical problem that needs to be resolved.

Troubleshooting the mystery circuit

Troubleshooting a circuit that fails to operate as expected is an art in itself, but there are some useful guidelines that you can follow.

Re-check all the circuit connections, component labels and orientations. Improperly installed ICs may have been damaged and would have to be replaced.
Disconnect the logic probe from IC2 pin 6 and re-check for power at the supply rails, as well as the IC1 and IC2 power pins.

To further debug and analize the circuit, you will use the voltmeter and oscilloscope, to be done in the next lab.