Recently I received boards for a sensor array from PCBWay. This boards were made in a very good quality considering the low price level. I really like the green solder mask they use, it creates a nice optical effect shifting the green colour towards yellow somehow. The solder mask produces a very nice contrast between […]
Tag / pcb
|Surface Finish||HASL Lead Free|
|Minimum Solder Mask Dam||0.4mm↑|
|Plated Half-holes / Castellated Holes||No|
|Minimum Drill Hole Size||0.3mm|
|Base Material||FR-4 TG130|
|No. of Layers||2 layers|
|Blind or Buried Vias||No|
|Trace Width / Spacing||6/6 mil|
I payed $27.40 for five boards with the option shown above and there were additional $20 shipping costs.
My board design has a very low quality class B4: Minimum drill size is 0.35mm, minimum trace size and spacing is 0.2mm.
Ordering and Shipping
The order process was very simple. The website provides an assistant with all possible options and calculates a quote in real time. I just noticed these minor things:
- The shipping cost is not displayed in this quote.
- The dimensions were not correctly extracted from my Gerber files.
The production of the boards and the shipping was quite fast, the whole process only took 10 days until the packet with the boards arrived.
The boards were well protected in the package, so there were no scratches from the shipping of the boards.
The boards have a good quality for the chosen options and the price. The alignment of the layers is not perfect, but everything is in an acceptable range.
The front side of the two boards. Continue Reading
I received the foot parts of the plant watering sensor from Eurocircuits. As you can see, they have the same great quality as the head parts. Eurocircuits removes any bridges from the boards in a very clean way, so you get the boards with exactly the shape you designed. This saves a lot of work […]
I ordered a single panel as a test for the production version of the plant watering sensor and I got astonishing perfect panels from Eurocircuits. Even I only ordered just one, I got three perfect panels in gold. Thank you very much Eurocircuits! As you can see from the photos, the quality of the panels […]
This is the fifth part of the meta-tutorial, where I talk about designing a cheap plant watering sensor. If you did not already read the first, second, third and fourth part, please do it now. These parts contain a lot information which lead to this point of the tutorial.
The fourth part ended with step 20, where I did usability tests and stability tests using the preliminary firmware. This article will focus on designing the final board for the project.
Step 21: Design the Final Board
Designing a good board is like one of these puzzles with quadratic tiles, where you try to lay down a 3✕3 set where all edges match. Often a small change result in many follow up changes, so you have to rip-up a lot of routes and design them in a new way.
My goals for the board were:
- Everything, except the two LEDs, should go to the top side of the board.
- Reduce the amount of vias to the absolute minimum.
- Create a ground pour, especially around the oscillator part, to reduce noise.
- Move the button as far as possible from the oscillator to minimise the influence if the user presses the button.
- Make it as small as possible.
I worked with small iterations, checking the design after each iteration and checked the design against my goals. To keep track of the changes, I versioned each larger iteration. This way I could go back at a later stage for comparison or if a change did not turn out well.
I worked with Autodesk Eagle to create the board. This tool is in the current state far from perfect, but it is cheap and has all required features for the task. For me personally, these are the features I need to design a board:
- Smart routing editor which is linked to the schema.
- Quick and easy way to create vias and see the required connections.
- Good library support for symbols and packages.
- Design rule checks.
- Quick board preview to check label placement and design.
I described some issues of Eagle in this post:
As you can see, these are not very advanced features and are supported by almost all good board editors. I never use the auto router, because I do not have time pressure or have to do repetitive tasks. Continue Reading
As mentioned in my article about designing a cheap plant watering sensor, I built a small adapter which can be used to pre-program the ATtiny13A. This is necessary, because once soldered on the board, I only have a debugWire interface, which has to be enabled first.
The adapter has a small 50mil JTAG header, where the Atmel ICE can be connected with the board. There is also room for a USB mini jack, which is used to power the MCU while programming. A small on-off switch is used to power the MCU and a LED is placed as indicator to see if the MCU has power. The assembled board looks like this:
One of the DIL/ZIF adapters is mounted on top of the female headers. Most of the adapters for SO-8, SO-14 and SO-16 will work with this board. Continue Reading
This is the second part of the meta-tutorial, where I talk about designing a cheap plant watering sensor. If you did not already read the first part, please do it now. It contains a lot information about constraints and decisions made which lead to this point.
The first part ended with step 11, building a working prototype with the selected key components. So let us start with the next steps in this journey.
Step 12: Analyse and Measure the Prototype
Never forget why you actually built a prototype. It is your tool to verify all assumptions you made in the design phase. To do this you need the right measuring instruments.
The Power Usage
I start measuring the current of the circuit. This will show if my assumptions about the battery life will be true. For this test I use a multimeter which has a good resolution measuring in the µA range. The multimeter I use is the Testo 760-3 which is not a very well known brand. Multimeters are usually really poor at measuring low currents on low voltages, so let us see if this will work.
I also use a Fluke 114, but this one has no current measurement. It is sometimes very handy to have two multimeters, one to measure the voltage and a second one to measure the current.
For the first test I program the MCU to do all the tests in a loop and connect the power directly to the second part of the circuit. Now the power is always on and I can measure the current used by the MCU while doing the measurement.
Just running, doing the measurement of the oscillator, the second part of the circuit uses at maximum ~1.2mA. This measurement phase should be as short as possible. Later we will analyse the timing. Continue Reading
Hurray! I just finished the final Outmoded Sequencer device. The tuning of all frequencies was way faster than I expected, because I used a new method. Have a look at the following photo gallery before I tell you some details. You can see the device is build like a control desk, with the PCB a […]
Here a short update on the progress with the final Outmoded Sequencer project. I did the whole assembly of the final PCB and connected everything. You can see part of the soldering process in the following video: I accidentally cut a route on the bottom of the PCB, so I had to fix this with […]