A collection of tips and how to's that are spread around the blog.
Let's build the MaxESP3
[Scroll down for MiniPBC2 Assembly]
OK, I got a little ahead of you and placed the resistors and junction pins.
Next let's place the caps.
On underside of the board are are the S310FA Schottky diodes. They are surface mount devices. If you prefer legged axial SB3100 diodes can be used in the holes provided. To reduce congestion under the RTC module I placed the AUX7 junction on the underside. Check with you enclosure to see if this fits. Maybe an external switch is in order?
Time for the female headers. I use an old driver to keep things aligned. When soldering the headers keep them close to the surface of the PCB there is not a lot of clearance in the metal enclosure.
Done with the driver headers, now do those for the ESP32 devboard, RTC and D1 mini wifi if they are to be used.
Time for the outputs; 2 RJ-45, 2 - 4 screw terminals and one mini phone jack. Might as well place the fuse while we're here.
Now on to the other end of the board. Place the RJ-12, the DE-9 connectors and the 5V power regulator.
Last is the 12V power regulator. The is only required if you plan to use a power supply rated at more than 15V. The regulator requires at least that much to put out 12V. Otherwise just jump the header pins for Vin and Vout.
Well, about 70 MiniPCBv2 kits have gone out the door and very little seems to be happening at Alibaba's facility in San Bruno, CA where my orders go to die, so I thought that I should at least put up some information on the Mini kit.
Here's one laid out for assembly.
So let's build it!
I like to start like Steve Schwartz does with the smaller parts first. Not only can it be difficult to do it when space gets tighter, the smaller parts are generally of lower height, which helps keeping them seated until soldered.
Here I've placed the 6 ceramic capacitors (5 - 104 & 1 - 33). The 0.33µF is C5 2nd from the top at the right. All the others are 104s.
Only one diode D5. Note the polarity! Just 5 resistors. RP1 (on left just below Teensy) is the one to watch. On one side is inscribed • 2221. The pin under the • is positioned furthest to the left. The Axial resistors have no such polarities, but the do have values.
As you place these components spread the legs a bit to keep them in place when you turn over the board.
You want to leave a lump of solder that looks a bit like a Hersey Kiss. When you inspect the top of the board you should see that solder has wicked up through the via. Remember the heat of the iron will draw the solder to it.
Now place the electrolytic caps. Polarity again! These caps have a positive and negative pin. The poles are indicated on the PCB by a "+". There is a vertical band on the cap with "-" signs on to show the negative pin. The negative pole or ground is indicated by a white finger nail in the cap symbol.
Let's get into power with the voltage regulator. I've made a running change in the parts in the MiniPCBv2. The HW-813 has DC-DC power converter has caused some confusion and problems. It was intended as a replacement for the BOM's OKI78SR5/1.5W36C. The OKI part is about $6 delivered. The HW-813 was under a buck.
I've replaced it with the MP1584EN DC-DC power converter, which is a design very similar to the OKI. The MP1584EN is preset at 5V output. No traces have to be cut or is any bridging necessary as was the case with the HW-613. It is shipped with the pins installed. It costs a little more than a buck.
Now the power jack, fuse holder & switch header (1), a 2 pin length of male header.
The jack (3) is of the "M" coaxial type 5.5mm barrel and 2.2mm center pin. The fuse holder takes the "Micro" blade type. Use either a 2 or 3 amp.
Above the jack and fuse is the ST-4 port. This port is for the use of an autoguider, the Smart Hand Controller or the Not-So-Smart Hand Controller or as they like to call them in PW world, human interface devices. There are two parts involved here, the RJ-12 jack and a 2 pin length of male header.
The two pin header is jumped only when whatever is connected to the port needs 5V power. A shunt is used to close the circuit in that case.
Time for the female headers. These are a bit of pain to keep in place while soldering. I use a trick. After I've soldered another component there will usually be drop on solder on the tip of the iron. Rather that wiping it off I place it over one of the end female header holes. It's not enough to fill the hole, just enough to tack the header in place.
The header's pins are lined up in their holes and it and the PCB are held in place by your finger and thumb while the iron heats the solder. When the solder melts the pin will fall in place and should stay there while the board is put on the bench to solder the rest of the pins. Before soldering the header check that it's fairly perpendicular to the plane of the PCB. A light touch with the iron on end pin can ease a little adjustment. Solder at least one other pin to fully secure the header before fully soldering the end pin. Note the light dab of solder at the end pin of the header holes on the left.
With that out of the way we can solder the semiconductors to their male headers. Start by inserting the male pins into the female headers. Then position the module on the pins. A little adjustment of the headers may be needed to line everything up. Careful with the Teensy it can sit with the pins out of position.
Now there are some decisions to make. At the end of the PCB opposite the ST-4 port are four additional ports for the step motor, PEC, limit sense, and illuminated reticle connections. The kit includes connectors for these connections, however there are other hook ups to consider. For PEC, limit sense and the reticle you can use the mini phone jack connectors provided or run wires to another type. For the step motors RJ-45 8P/8C jacks are provided.
The idea behind the jacks is to use Ethernet patch cables. As the conductors used in these cables are quite small two of each are used to for each pole of the step motor. And that is certainly an option. In my experience connectors should be avoided if there is an option to use solder. And if mechanical connectors are to be used then modular telephone connectors aren't my first choice. Now some motors come with fairly nice cables with connectors for male headers as on the right below. These are fine for a while but over time they can loosen and lose continuity. The Dupont type can be removed from their shell and soldered in place. I use hot melt glue or shrink tubing for insulation.
On the left are another option, screw terminals.
If you'd rather use one of these options let me know and I can substitute them for the RJs.
What's left? Well there's the three LEDs, Status 1 through 3. 1 and 2 are power and tracking. #3 has something to do with limit sense? Positioning the LEDs really is going to vary with your enclosure design. Power and tracking are next to the ST-4 jack and can be soldered with their legs in most cases. The longer leg is the anode and goes in the through hole on the right when viewed as below.
Lastly is the power switch. solder the switch lead to the switch and when ready feed it in through its hole in the enclosure and connect it to its header. There is no reason that you can't just use a shunt on the switch header and use the power jack to control power.
That's all, I can think of. Hope it helps.