18. Install R12, a 10K ohm resistor (brown-black-orange). 19. Install R16, a 100 ohm resistor (brown-black-brown). 20. Install R13, a 10K ohm resistor (brown-black-orange). 21. Install R17, a 100 ohm resistor (brown-black-brown). 22. Locate and install K1, one of the large white relays 23. Install relay K2. 24. Install relay K3. 25. Install K4, the last relay. Great job… you just finished building the relay driver circuit! The transistors (Q1 through Q4) energize their respective relays when they are turned on and off by the micro-controller (U1). Next we’ll build the power supply section. 26. Install VR1, the 7805 voltage regulator.
Install the three leads as shown on the silkscreen and gently bend the part over to match the silkscreen layout. Affix VR1 to the circuit board using the provided #4x40 screw and kepnut; then solder all three leads. This part “smoothes” out any ripple that may still be present on the main input supply voltage and provides us with the needed 5 VDC the ICs operate on. 27. Install C3, the 100 µF electrolytic capacitor. This part must be installed properly for it to function. In fact, this capacitor has the potential to explode if installed in reverse polarity! The PC board silkscreen shows the positive hole and the band on the capacitor shows the negative side.
You’ll also notice that the lead closest to the stripe is shorter the other lead; this also indicates the negative side. 28. Install C4, the 10 µF electrolytic capacitor. Watch that polarity! 29. Install D1, the last 1N4004 diode. Watch your orientation like you did for D5 through D8. With exception of the power switch, which we’ll install a bit later, you just finished the power supply section! Diode D1 acts as a polarity safety net so that you don’t accidentally harm the unit should a miss wired plug be used. Since diodes only conduct in one direction, the unit will only power up if a positive tip DC power plug is hooked up to J5.
Capacitors C3 and C4 work with VR1 to provide you with a well regulated 5 VDC supply needed to power the ICs. 30. Install the 20 pin DIP socket for U1, the 68HC908JK1 micro-controller IC. It doesn’t matter which way the socket is orientated, as long as the chip is place in the socket the correctly. You can bend two of the corner leads out slightly to hold the socket in place when you flip the board over to solder it in. Make sure all 20 pins are through the holes and then solder each one. Check your solder joints for even flow before moving on. DCI1 • 14