Offboard connections

The boards are connected by single-stranded PVC insulated connecting wires. The insulation is stripped from the ends of each wire for about 5 mm. The table below lists the connections needed. Cut the wires as short as conveniently possible.

FROM

Function

TO

Board

Socket

Board

Socket

Controller

E1

Positive supply

Switching

A1

Switching

A2

Positive supply

Motor control

C2

Motor control

C1

Positive supply

Power switch S1*

Power switch S1 (common) *

Positive supply

Battery positive

Controller

E12

0 V line

Motor control

E2

Motor control

E1

0 V line

Switching

C1

Switching

C2

0 V line

Battery negative

Controller

L1

Motor control A

Motor control

G2

Controller

M1

Motor control B

Motor control

H2

Motor control

G20

Motor output A

Motor M1 terminal*

Motor control

H20

Motor output B

Motor M1 terminal*

Controller

G12

LDR1

Switching

F1

Controller

F12

Comp. 1 ref.

Switching

B1

Controller

N12

Buzzer

Switching

A22

Controller

J1

D1and D2

Switching

C22

Controller

I1

D3

Switching

E22

In a few cases, indicated by * in the socket columns of the table, the wires are soldered to the terminals.

The positive supply also goes to the off-board LEDs and LDRs. For neatness, this line and the connections returning from the components are best assembled as a unit.

FRONT

FRONT

Connections between the Switching board and the LEDs/LDRs (diagrammatic).

The positive line is drawn in the diagram as a continuous line. It is a length of bare connection wire which runs from the anode of D1 (front right), across the front of the body, to half-way along the left side. Then it continues to the positive terminal of the power switch S1. A small loop is twisted in this line level with each of the components it visits: D1, LDR1, D2, D3 and LDR2. There is insulated sleeving between these points. The leads of the components are cut short, bent into hooks, and hooked into the loops in the positive line. The loops and hooks are squeezed together with pliers and the joints are soldered.

Four other lines run back from the non-positive terminal of each component to a socket on the switching board. One of these serves two components, the cathodes of D1 and D2. These connections use insulated single-stranded connecting wire and are wound spirally around the positive line to give the assembly some rigidity.

The wired assembly is supported by two small cable clips, situated on either side of LDR1. These self-adhesive clips do not adhere to the plastic of the box, so they are bolted in place with M2 bolts.

The interior of the box when wiring is finished, as seen from below. Most of the connections are between the Processor board and Switching board, but the wiring has been routed away from the processor socket so that it does not interfere with putting the PIC into its socket and removing it. The connections to the LED/LDR assembly can be seen going off to the left (right in the photo), near the label 'Velcro'. The main switch SI can just be picked out between the Velcro and the buzzer.

The interior of the box when wiring is finished, as seen from below. Most of the connections are between the Processor board and Switching board, but the wiring has been routed away from the processor socket so that it does not interfere with putting the PIC into its socket and removing it. The connections to the LED/LDR assembly can be seen going off to the left (right in the photo), near the label 'Velcro'. The main switch SI can just be picked out between the Velcro and the buzzer.

The patch of Velcro is to hold the battery box in place. The box holds four AAA rechargeable NiMH cells and has a matching Velcro patch on its side. It connects to the circuit by a standard PP3 battery connector.

This completes the wiring but it is essential to test everything at this stage. Routine testing is described on pp. 102-103. The main stages are:

• Test for continuity on the 0 V line and positive supply line.

• Test for short circuits between these two lines.

• With the PIC removed from its socket, switch on the power and check that each board and off-board component receives power.

• At the PIC socket apply a positive voltage to each output line using the table opposite to identify test points. The LEDs and buzzer should operate. With a positive and 0 V lead applied to pins 8 and 9, the motor should run forward or in reverse.

• Use a test meter to see that the voltage from the LDRs is a reasonable value with the LDRs exposed to light and shaded.

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