Assembling the ATTiny_Daemon Hardware
Assembling the ATTiny_Daemon is quite simple and can be done without problems even if you are not experienced in soldering.
First of all you need to order the PCB from a PCB manufacturer. As an alternative you could build the system on a breadboard to test it first, or wire it up on some protoboard. But today ordering a few PCBs is so cheap that in my opinion it is the best way to go. To order the PCB you upload the Gerber files to the manufacturer and walk through the respective order process.
You can find all the parts in the bill of materials or BOM that I try to add to each of the versions (for the version 1.8 you can download it here: BOM.csv). It contains the part names, designators (i.e. the names on the PCB), the quantities etc., in other words this is your shopping list for the parts. Here is the list:
| Name | Designator | Footprint | Quantity | Manufacturer Part |
|---|---|---|---|---|
| 1N4148 | D1 | DO-35 | 1 | 1N4448 |
| 330 | R1 | AXIAL-0.3 | 1 | ? |
| 100K | R2,R3 | AXIAL-0.3 | 2 | ? |
| Header | P2 | HDR-6X1/2.54 | 1 | Header-Female-2.54_1x6 |
| RPi | H1 | DIP-2X2.54MM-4P | 1 | DS1023-2*2SF11 |
| 0.1u | C1 | RAD-0.1 | 1 | ? |
| ATTINY | U1 | DIP-8 | 1 | ATTINY85-20PU |
| Jumper | P1 | HDR-3X1/2.54 | 1 | Header-Female-2.54_1x3 |
| LED-3MM | LED1 | LED-3MM/2.54 | 1 | 204-10SURD/S530-A3 |
This is mostly self-explaining, but there are a few minor things worth mentioning.
The 1N4148 is only one example of a diode you can use, a 1N4001-1N4007 is equally good if you have it lying around (the different forward voltage will be compensated by the configuration of the ATTiny_Daemon).
The value of the resistors R2 and R3 is not critical either, as long as they are pretty high(they are used as a voltage divider, which means that they are dissipating the power running through them as heat. With a sum of 200K we have around 88uW, which is acceptable. The ATTiny-Datasheet gives a maximum value of 100K for a series resistor to the ADC in chapter 17.8 (see graphics), which is why we have this value for R2 and R3. You can even choose an asymmetric voltage divider (if you do not have 2 resistors of the same resistance) and we can compensate for this in the configuration as well.
RPi is a female header that in the case of the shim variant has to be at least 2x2, but nicer is 3x2 to give it a bit of additional stability.
Get all the parts, the PCB, a good light on your workbench, the tools you will be using and a smoke extractor, and you are all set.
The best way to assemble a PCB is to start with the parts with the lowest height and the lowest number of pins. One advantage is that your parts cannot fall off if you can press the PCB against the workbench and thus ensure that the parts stay where they should be, the second advantage is that it is easier to fix mistakes (and they will happen...).
Do not solder the capacitor yet, because its placement under the IC socket warrants special consideration.
In our case it is the diode and the 3 resistors which are labelled on the PCB. Bend the wires carefully and insert the parts into the PCB holes. It is important to orient the diode correctly, so check it twice.
Now bend the wires outward on the backside so that the parts are fixated and cannot move.
Solder each of the wires. What I do with all parts is to first solder one pin to stop the part moving, the solder the second pin, then reheat the first solder joint shortly to guarantee that it is a clean solder joint (but that is only me...).
Then cut all the wires with a side cutter.
The next step is the 6-pin header. You can either use a female or a male pin header, obviously you need to use the opposite for the cables. I like to use the female header here because I think that having these pins exposed might be risky, but the opposite having the cables expose e.g. the battery power can be seen as equally problematic. Ymmv...
There are multiple ways to solder it to the PCB. One easy way is to simply solder the header flat to the underside of the PCB, and I have designed the pads on the underside so that this can be done without problems.
What I'm doing though is to solder it on the component side after bending its pins into a 90-degree angle. Why? One argument is that this way the connection is a bit more stable (but this might not be true). The better argument is that this way it pin header does add less height to the PCB. But even this is not really a good argument. So choose whichever way fits your approach best.
If you use two female 3-pin headers then connect them using a spare male pin header to ensure that they are more or less in parallel.
As you can see on the picture my headers are not perfectly aligned, but I can live with the result.
Next is the LED. If you examine your LED closely you can see a part lower ring that is part of the housing of the LED that is flat. Align this part with the drawing on the PCB (i.e., the flat part has to be oriented towards the connector we just soldered in).
Now bend the LED so that the housing is placed near the edge of the PCB, bend its legs outward so that it can't fall out and solder it in.
Next is the IC socket. Insert it, ensure that the indentation in the socket matches the drawing on the PCB and solder it in.
Now comes the capacitor. Insert its pins carefully into the holes in the middle of the IC socket and push it in.
There is not much wiggle room, and this is why we didn't solder the capacitor in the beginning, because this would have made it more problematic to solder the IC socket. Solder it
Now comes the male pin header. Insert it and solder its pins.
The last step is soldering the connector to the RPi, for which I used 2 female 3x1 connectors (the same that I used for the other connector).
Now you are done. But in a final, optional step you could clean the bottom side of the PCB with some alcohol to get rid of the flux residue. This is good, because flux and flux residue can be quite corrosive and, over the years, can damage your board in ways that can be quite problematic to find. But it is also good because it allows you to visually inspect your board and examine every solder joint in detail to decide whether it should be reworked.
Congratulations.