• Schematic
• PCB Layout

Assembly instructions

The first items to mount are the ten 0.1uF axial capacitors. Capacitors are not very static or heat sensitive, so they are a good place to get used to soldering if you're not completely comfortable. These capacitors are all the same and come attached together in your bag of parts, so they should be easy to identify. In order to mount them, you must first bend the leads (wires) to a ninety-degree angle so that the leads will fit into the holes in the PCB. Once the leads are bent, you can insert the capacitors into their locations on the PCB. Do one then test. It may take a few to get the spacing right - but this is the spacing used throughout the board so once you get it everything else will turn out right. It doesn't have to be exact. After inserting each capacitor, spread the leads a bit on the back side of the board to hold the capacitor in place. It makes it easier if you rest the board on something like a roll of box tape - this elevates it off your workbench and lets the leads hang down without obstruction.

After soldering, you should make it a practice to visually inspect each completed joint. Take a good look to make sure the solder fills the hole in the PCB and to make sure that all the leads have been soldered. Once you've looked it over and corrected any problems, clip off the excess leads on the back side of the board so they don't stick out too far.

Now for the resistors. See Appendix for resistor identification - there are a lot of different values included in this kit. First step is to lay out all the resistors and identify them. Compare against list of materials (insert resistor component list here). Note that you are given one extra 56 Ohm resistor - save this for later. If you have any doubts proceed by the process of elimination. Colors aren't always easy to distinguish on resistor bodies. Again, resistors aren't very sensitive to static or heat so they are a good way to get used to soldering.

Bend the resistors leads exactly the same way you did the capacitor leads. The component bodies are about the same size, and the hole separation on the PCB is the same. Once again, insert all the resistors at once, turn over and tack down one lead, turn over and inspect, make and necessary corrections, then finish soldering.

Now you've had plenty of practice - 23 components soldered! Time to move on to the harder parts. Next, we're going to put in the Diode at D1. This is the first polarized component on the board. Meaning, unlike the capacitors and resistors we have encountered so far, diodes must be inserted in a particular way - there is a difference between pin 1 and pin 2, and if you insert it the wrong way your board won't work. The appendix discusses polarized components and how to recognize which orientation is the proper one.

Diodes are also static sensitive - electrostatic discharges from touching these components can generate thousands of volts at the lead - enough to damage the component. It is good practice to keep yourself grounded while soldering these. Wrist strap, touching ground, etc. They are also heat sensitive - if you allow the soldering iron to remain on the part for too long, the temperature will damage the part. You have a few seconds - solder the part then move on. If you make a mistake, give it time to cool down before trying to correct it.

Bend the diode leads just like you did for the capacitors and resistors, then insert the diode into the board. The silkscreen on the board shows an outline of the diode, with a triangle and a stripe. The point of the triangle is towards the stripe. The end of the diode with the band around it matches up with the stripe on the silkscreen. See the Appendix for an illustration.

Integrated circuit chips. There are two we are going to solder in this step, the MAX667 Power regulator (U2) and the DS232A serial transmitter/receiver (U3).

Location U4 is reserved for the optional EEPROM. It should be left unstuffed in the default configuration - don't accidentally put the MAX667 in this location! U4 is used to add a serial EEPROM to the Mark III. This EEPROM adds up to 256Kbits of memory to the PIC, for general use. If you choose to use an OOPic instead of a PIC, this EEPROM is mandatory. If you use just a regular PIC, the EEPROM can be useful because the PIC only provides about 300 some odd bytes of RAM storage.

DIPs are polarized and static sensitive. Find pin 1 and make sure that the DIP is oriented properly. Insert into board. The legs of the DIP may be spread too far apart to insert - if so you will need to squeeze them together before you can insert the chip. The easiest way to do this is to insert the legs on one side of the chip halfway, then while holding the chip by the ends apply gentle pressure to simultaneously bend the all legs that are already in the board. Turn board over. Fasten opposite corners with a quick dab of solder then turn back over and check to make sure chips are properly seated.

A 40-pin socket is provided for the PIC chip; this allows the PIC to be easily removed or replaced and also raises the PIC off the surface of the printed circuit board, making room for some resistors to sit underneath the PIC. The socket has a semi-circular notch cut into one end - align this with the corresponding notch shown on the silkscreen. Just like you did with the integrated circuits in the previous step, use a tiny bit of solder to fasten two opposite corners of the socket, then turn the board over and examine it closely to make sure the socket is properly seated. When you are convinced it is, you can solder the remaining pins. Don't forget to go back and make sure the two original corners you soldered get properly fastened.

Tact switch. This push-button switch is used to reset the PIC. The reset switch only fits in two ways, rotated 180 degrees from each other. Either way will work.

Next we will solder in the two small 3-pin shrouded headers (J5 and J6). Notch facing toward the center of the board. Asymmetric - check to make sure that the outline on the PCB matches up with the header. If the PCB outline sticks out a lot, you probably have it backwards.

Electrolytic capacitors. Check for the "-" pin (called the cathode), labeled on the capacitor body with a broad white stripe. The cathode is also the shorter lead. Make sure it goes in the correct hole. The silkscreen has a "+" next to the square pad, the round pad is where the "-" pin goes. This is very important - if power is applied to an electrolytic capacitor in the wrong orientation it may explode! See the Appendix for an illustration.

Resonator Y1. Resonator is not polarized, insert it either way.

LEDs. Light Emitting Diodes - everything we discussed re polarization, heat, static applies here as well. The LEDs are inserted so that the short lead goes into the square pad. The square pad is shaded white on the silkscreen.

Headers, 40-pin and 6-pin at the same time, then the two 3-pin. Again, tack corners (or just one pin, in the case of the 3-pin headers) then turn over to make sure that it is seated properly before doing the final soldering.

Power jack (the black, three-position terminal block) should be inserted so that the wire receptacles face the outside of the printed circuit board.

I²C header (5-pin white header) oriented so that the back (tension relief) is against the DB9 connector.

Power Switch can be inserted either way.

DB9 Serial connector only fits one way. Be sure to solder the locking standoffs to the PCB - this provides strain relief as well as a good ground.