We can start to mount the Main PCB assembly from the resistors and capacitors. The rear side of the PCB is "U" shaped in order to accept the 70mm fan cooler mounted very tight to the heatsink. The PCB is a single side, easy to produce and procure exactly as the other PCB on the Universal Charger. The resistors values are not critical the only important aspect is that the values on the input differential stage (R5,R6,R25 and R26) must be matched (R5=R25 and R6=R26) in order to maximize the differential amplifier performances. All the capacitors (except the two 15-18pF for PIC oscillator load) are 100 nF multilayer ceramic type.

Then we mount the IC sockets (28 pins for PIC, 16 pin for MAX232 (or equivalent) and 14 pins for LM324). Together we can mount th NPN transistor (BC 337 or equivalent), the two 1N4148 diodes, the contrast adjustement trimmer, the 20MHz PIC crystal and the small strip connectors.

Then we mount the TO-220 regulators and transistors, the small capacitance electrolytic capacitors, the electromagnetic buzzer and the current pick-up. Very high care in the positioning of the polarized components, see the reference marking on the top silkscreen of the PCB. The LM7812 (U54) regulator must be mounted only in case the power supply exceed the 15V and we use a 12V fan cooler, in case of power supply lower than 15V the pin 1 and 3 of the regulator must be shorted together. For large power supply voltages (greater than 18-20V) a separate heat sink for 7812 and 7805 must be mounted.

This particular shows the circuital alternative that allows to mount the two current pick-ups, the ACS 750 (752 or 756 are good) from Allegro Micro or LTS25-NP from LEM. The ACS 750 has a bigger sensitivity (40mV/A versus 25mV/A of the LTS25-NP), is cheaper than the LTS device and very easy to mount not requiring a separate high current wiring.

The last two components are the big electrolytic capacitor for power supply regulation and the complete assembly of the power heatsink (not shown). This last phase complete the Universal Charger assembly.