Nice troubleshooting Steve. That must have been frustrating to debug since the first board worked fine. I imagine this would be an issue folks might run into when they are having their boards mass produced, and the CM opts to use a different part than what’s in the BOM. It reminds me of one of Dave’s videos where he’s troubleshooting a similar situation with an op amp on a new batch of his µCurrent’s: https://youtu.be/1VlKoR0ldIE.
Were you able to figure out what the difference was between those 2 LEDs that was causing the issue?
It’s also possible that the first board didn’t work fine, it just had fewer errors.
Adding relatively high current loads to signal lines is generally not a good idea. Unfortunately VCC does not put enough info on their datasheet to be able to compare the two LEDs. But none of the datasheets list the LED’s capacitance which could also be contributing to the problem. Having a separate driver for the LEDs, such as a transistor as suggested, is the safest approach.
I have been picked up on this before. I need to watch my terminology and down grade “work fine” to “seemingly behave correctly” until every spike and pulse can be accounted for.
I already posted about a AA-Cell adapter where I wanted to extend what I learned about custom board shapes from the “Blinky-Bear” project to something a little more practical. I received the boards for the AA-Cell Adapter while ago and managed to get some time to assemble and test. Everything worked find ant they fitted together nicely. The custom board shape was not the end of the mechanical challenges! I needed to modify the end cap so that the board will fit and also make a good contact with the plus and minus poles of the device. This would mean having only have one chance since I would have to destroy the end cap to make the change. The alternative is to 3D print a new end cap. I have not had a 3D project before, so here were a few more skills to pick up.
I wanted to try out Fusion 360 and this seemed a simple enough project to make a start. The modelling is not exactly easy since the original seems to be round at the base and slightly elliptical at the opening. The thickness of the walls is also not uniform. I started with a base model and decided to just give it a go. It turned out it did not fit as I had used the “shell tool” which made the walls of the cap parallel to the outside, which were tapered. The piece of the main body that fits into the end cap is more cylinder like. Taking what I had already learned, I then created a whole new model. This time cutting out a cylinder from the end cap body rather than using the “shell tool”. So it was off to the local FabLab to print out Attempt #2. This result was much better and the cap fitted neatly on the main body part. I added a small self-made copper spring for good measure to take up any slack that might be in the housing. However, this was not going to be my problem - The base was too thick and the USB mini plug could not go in far enough to make a solid connection.
I changed the model to make the base thinner and now Attempt #3 does the job. It fits neatly on the main body and the USB plug can make a good connection.
I think in the last twelve months or so of Contextual Electronics, I feel it is the mechanical aspects pose the biggest hurdles when developing something new and where I feel I have spent most of my time. Sure, getting the electronics right has its challenges. But trying to get these things to fit neatly together needs a lot more consideration. I guess, electronics seems simpler because if it does not work, then a component value change, wire bridge or lifting a pin might sort out the issue. But with the mechanical aspects, it can mean a whole new spin of the housing or even a board.
Very cool! Nice work! I agree that the mechanical/fab part is a hindrance. I’ve got some projects but not sure how to build the housing for something that is not a straight line, such as bike frame shapes, where the radius changes over the extent of where I want to attach something.
Looks good Steve! It looks like the third time was the charm. That final part came out great. Were there any Fusion 360 tutorials that you found useful for learning this stuff? The cost of 3D printers are so cheap now I may try to get one under the christmas tree this year.
It ws certainly a case of third time lucky Each time I was confident that it would simply be right. But then there was something else that I had not considered. Taking the measurements off a relatively small original part was not easy. I also struggled a bit with how to model the part as simple as possible since my niveau of 3D modelling is still novice. I was finding variences in wall thicknesses and other aspects were neither staight nor round. So I opted for a best guess/fit approach.
When getting into Fusion I worked through the first few set of tutorials from Autodesk, especially the UI where I learned the “S” hot key becomes a good friend.
A 3D printer to have in the Lab would be very convenient. For me, the price is one aspect, but the benchspace is probably worth more. I am very fortunate to be able to cycle 5 minutes to the nearest FabLab, and I am enjoying just talking to others about their projects while the part prints. I work from home so I see this as a substitute for the coffee machine at the office
I was Looking for a quick exercise to try out KiCAD 5.0, so I decided to go back to the first exercise I never really finished - Getting to Blinky! The original Getting to Blinky series is what convinced me that KiCAD was what I needed for my purposes and made me aware of Contextual Electronics.
I had a rough start as I downloaded one of the original archives. This install would throw an error when clicking on the Tools menu. Apparently the archive was updated shortly after the release. I downloaded it again and now it is fine. That was the only major issue.
When opening an existing schematic, I did have a bit of a doubt. I get the dialogue to re-map the symbols. My first fear was what that would mean in 4.0 - symbols suddenly appear in a different size and things don’t quite connect any more. From a brief look around, it seems the best is to accept the defaults. I have not looked into the details yet to know any better. Needless to say, accepting the defaults for the couple of projects I have tried this on has not shown any surprises.
For a new project like the Blinky, it went smoothly. The only thing that lost me was the renaming and re-locating the OpenGL option for in Pcbnew. The hot-key has not changed, just the name. It used to be under View. But they are now located under Preferences.
I found the explanation and now it all makes sense. Legacy (F9), the old layout canvas and will be removed at some stage. Modern Tool set (F11), is the preferred canvas and is renamed from OpenGL. This name had no real functional meaning with respect to the Pcbnew. The Modern Tool set Fallback (F12) is in case F11 does not work i.e. problems with the graphics drivers.
Once that was understood, it was clear sailing. I also noticed there is an “add vias” tool. This really simplifies things like via stitching as I don’t have to create a special footprint for the purpose.
There is more to explore in Eeschema too… a Symbol Field Editor in speadsheet format where it looks like the component values can be updated. This will be handy for making corrections etc before creating the BOM. One of the reasons I have never really used the BOM feature that much is the back and forth making corrections.
I thought I would try my hand at writing a script for KiCAD. I created a small script to archive the F.Paste, B.Paste and the Edge.Cuts layers to a zip file for uploading to OSH Stencils. I have posted the scripts to my GitHub Repository. I found I needed to create two versions of the script as I had some issues working with External Plugins in KiCAD 5.0, Windows 10.
On Windows KiCAD - 5.0 Stable Release, I only have the “Tools->Scripting Console”. The script can be ran from there. I also have a nightly build on Ubuntu (virtual environment). This install has the “Tools->External Plugins…” menu as described in the documentation.
A quick chat with our friends at KiCAD Info indicates that the menu option should be available for Windows in 5.0.1
Which is actually an exercise in custom/complex board design inspired by reverse mounted SMD LEDs.
I had to do a second revision to make the eyes blink once every 40 or so seconds using a 555 timer. I was caught out by not reading the datasheet (again). The 555 stops working below 4.5V so the 3V button cell was not going to cut it. Not to be defeated, I modified the cell holder to accommodate two cells. Now it works fine and can last up to 6 or so hours continuous running.
I have seen a circuit popping up now and again, particularly in the kits from ELV where they use a Gold-Cap (Super Capacitor or Electrostatic Double Layer Capacitor, if preferred) to provide a small backup supply to either enable a real-time clock to keep time during times of no power and in one case to enable time for the micro controller to clean things up before going into sleep mode.
For a project I am working on, I am keen to try this out. But before I race ahead and start building it in, I figured a more systematic approach would be to create my own Dev-board so that I could at least experiment with it in isolation to understand things like
How long will this last? and understand the power that can be delivered
Learn about the various sleep modes and how to wake from them.
How the ancillary part values can influence the behaviour.
I’ll be using an ATTiny20 as the microcontroller - one of my design constraints is to use up what I already have in stock. I have also broken out the GPIO to LEDs and Pin headers. This way I have a choice to use LEDs as indicators (and a type of programmable load) or use the for any other purpose as I figure out some tests.
I like to use theTag-Connect adaptors for my programming headers. I have opted to use the Legged version of the Tag-Connect on this board since I reckon it will be simpler to work with in the end than the No-Leg version. I was at Embedded World last week and had a chat with the chap from Tag-Connect. He gave me the idea to make the Tag-Connect Pads through-hole (using OSH Park’s minimum hole size). I am curious if this is going to work or if there is an issue with the annular ring! For routing, it certainly helped being able to utilise the bottom side to get around the “leg holes”.
On this board, I am also trying my hand at Castellated Edges.
Since the last post, I had to respin my Gold Cap Breakout board after realising an issue. I have finally been able to assemble this latest revision. Inspired by one of @ChrisGammell’s videos - I reduced the size of the Solder Past holes - just slightly. I realise there is an issue for fine pitched parts but in this case it was all good and I am very happy with the re-flow efforts. I did not have to apply any bodge or retouch any of the joints. The whole thing just worked!
I am also happy with the Tag-Connect programming header. As mentioned in the previous post, I changed the footprint to use Through-Hole vias for the pin-pads. This enabled some routing on the back side of the board, since getting around those “leg-holes” is quite tricky. The through-hole pads also have the added advantage of preventing a probe from slipping when using it as a test point.
I have been able to program the ATTiny20 with no issues at all. As a first cut and just to test that everything is working, I have setup one LED as a “heartbeat” and the rest of the LEDs as a rough and ready bar indicator to show the relative voltage level of the supply/Gold Cap. The next steps will be to work out some tests understand how long these will last based on the load.
Over Christmas I was thinking of other kitsch ways to use LEDs and thought of creating an animated “Tree Bauble”. At first I was imagining all sorts of advanced setups such as micro controller based animations. As the idea developed, it seemed to get simpler and simpler where I decided to use the slow self-blinking LEDs.
At one point, I was thinking to use flexible boards to attach some LEDs to. This gave way to an even simpler approach - soldering the LEDs directly to the “End Cap” boards.
I could not wait for the arrival of the intended 2512 sized current limiting resistor, so I just soldered a through-hole resistor onto the pads instead - another simplification.
This is just the first attempt. Something needs to be done about the power supply. The 9V battery is too big and heavy.
It has been a long while since doing any sort of write up. I have been more trying things out and experimenting rather than actually building anything at the moment. I did have a good look at the INA219 “Zerø-Drift, Bidirectional Current/Power Monitor With I2C Interface” and created a bit of a write up about my test and what I found.
The fun part was to brush the dust of the Current Sink or Swim. It was a great help in setting up a dummy load for the tests.
I had seen this come through via email, that was a great post! Was going to ask on there, do you have any cost contraints on your measurement system? If so, do you think the INA219 will be a good fit?
Each time I was confident that it would simply be right. But then there was something else that I had not considered. Taking the measurements off a relatively small original part was not easy. I also struggled a bit with how to model the part as simple as possible since my niveau of 3D modelling is still novice. I was finding variences in wall thicknesses and other aspects were neither staight nor round. So I opted for a best guess/fit approach.
