Wow thanks! That is so much cleaner! No guarantees I will be able to be this clean with my next one, but I promise it will be closer.
I suppose trying to make my symbol close to the datasheet is not the right idea. I think I need to do more to separate schematic and layout in my mind. I was probably thinking ‘if I can make the schematic like the real component I can get an idea of how hard it will be to layout’. I know that is not the right way to go about this and this just serves as a good lesson on that.
I am glad that no one was shocked at my choice of chip. I was a bit worried I had picked one that might not be workable with this example. If my math is correct this particular arrangement of resistors and capacitor should set the frequency at approximately 1.5 hertz.
According to what I read in the documentation it would have been fine for me to use a single resistor since I want a 50% duty cycle. I chose to use the two resistor configuration to match the course, but it would be nice to get verification that I could have done it the other way.
I will pick up some isopropyl alcohol and try to do better on the Blinky board. I was hoping to put in my parts order today, but I think I want to take another shot at the schematic before I go on to the layout. Since the video doesn’t talk about the battery or the battery footprint in the schematic section, I am waiting until I find out what I need to do there to order my parts.
I did set my led to a 1206 instead of an 0805 because I have plenty of 1206’s left over from the shine on board. I am assuming this should be ok. Even if it isn’t I want to do it so I can find out why I should know better.
I did some research on how 555 chips work and I believe I understand the basic idea and how the circuit design works. The 7555 chips seem a lot more confusing on the inside, so I was going with the datasheet until I was told otherwise. I think I understand what is being said about the RST catching noise from the surrounding circuits. I am not sure I understand how I would know that if I was coming up with my own project and using another type of chip for the first time. I suppose this is why there are reference designs.
I am hoping to get a better understanding as I go through more of the course material.
I understand your confusion, but there’s no doubt that the application note contains an error in the second circuit. IIRC Intersil was the original manufacturer, and their internal schematic reveals that pin 4 (RST) is indeed connected to the gate of a MOSFET, so it needs to be connected to a valid logic level to avoid unintended resets and other undesired actions.
FWIW I just submitted a support ticket (CAS-181415-B9Z8N8) to have this addressed. Most likely the datasheet won’t be changed, but I’m hoping that Maxim will at least issue an Errata. I used to be a component engineer, and these errors still really bug me!
This looks fine, though you might want to add a capacitor of 0.001uF to 0.01uF from pin 5 to ground for improved stability - particularly in electrically noisy environments. The internal node that connects to pin 5 is at high impedance and is susceptible to switching noise, so a small capacitor helps stabilize the voltage here (which determines the upper threshold for the timer). Instabilities at this node cause instability in frequency.
Thank you for looking at that and providing the explanation! I am not sure how much the frequency stability matters for this project, but it is great to have the information for when it really does matter.
I figured out that I have a bunch of 2450’s sitting around the house that I use in my alarm sensors that would be nice to use instead of the 2032 the video calls for. I am a bit scared I am making too many changes from the video, but then the point of all of this is to learn what I will need to know practically so I can make my own projects.
I was hoping someone could confirm the through hole dimensions for me on this. I read this drawing as 1.3 mm diameter on the pins. What is the 2- for?
Does that mean I should make the hole 2mm? Reading a bit on the net tells me the hole needs to be .15 to .25 larger than the diameter. Then that means my hole should be around 1.5mm ? How large should the copper ring be? 2.5mm ? or is that what the 2 is for?
It is a BH-32H-1
I haven’t ordered it yet. I wanted to make sure I knew how to make the footprint before I ordered it. I have the Digikey library downloaded. If it is there perhaps I can use that to double check the footprint I make. I just wanted to go through the exercise.
If you have done this already, my apologies: when designing your own footprint or appropriating a footprint that isn’t conventionally associated with the symbol you are using, it’s worth making sure pin numbers match up. Doubly so when it’s a power component. If the pin numbers on the cell symbol do not show in the schematic editor / eeschema, opening it in the symbol editor should let you identify them.
I fixed the battery cel to read CR2450 and fixed the active low pins thanks to the help from the KiCad 6.0 thread. I just did it right after the last picture was put up.
I am still waiting on my Getting to Blinky board to come in, but my components arrived today. Along with the SMD version of the 7555, I had ordered a through-hole version. I tested out the circuit on a breadboard successfully. I didn’t have the exact resistors or capacitors to get the frequency or duty cycle correct, but it does work:
One thing I find useful is to have SMD to breadboard breakout PCBs. You can buy them, but it is a lot cheaper to just get your own made, and they only take a few minutes to design. It’s useful when you are dealing with SMD only parts, and avoids having to buy DIP packages just for testing. Once you are finished you can easily remove the part with a hot air gun and then use it on your final project.
For desoldering ICs yes. For soldering ICs I prefer my soldering iron and drag soldering. However, you have to watch that you don’t end up with solder balls causing shorts if using a hot air gun.
If using stencils and paste, yes - although an oven would probably be preferable (something I’ve still not invested in - although I mostly get full/part assembled boards now so this rules out stencils).
For small parts - resistors and capacitors (0402/0603/0805+) - maybe. You have to play with the pressure to make sure things don’t blow away. With the right technique, and a pair of good tweezers, it is just as easy to solder them, although the hot air gun probably gives slightly better results. It’s also easier to get the parts straight with a hot air gun since the components move themselves into position, which is really cool to watch and never gets old.
Overall, it’s useful to have, but I wouldn’t say it is essential - at least early on. And, I wouldn’t be inclined to spend too much on one. Mine is really irritatingly noisy (Aoyue 968A+). One of my colleagues has one that is quieter but not as controllable. I can’t emphasise enough how much the noise annoys me. The rubber feet also leave black marks on anything it sits on - which is normally my nice HP power supply.
They are handy for removing stringing on 3D printed parts too. Oh and are fantastic for applying heat-shrink tubing.
My blinky boards finally came in. I am going to wait for the magnifying headset I ordered to come in before I solder these together, but I was very happy that my custom footprint for the battery holder seems to fit:
My family has had a bit of the flu lately (thankfully not COVID), so I haven’t felt much like doing anything; but I decided to take a shot at putting together my blinky board today and I absolutely ruined the first one. I tried to put the 7555 on by putting solder on each of the right side pads and then move the chip into place, but the solder hardened before I got it far enough over. I quickly figured out I didn’t know how to do a chip like this and then I further found out I had no idea how to de-solder something. I ended up ripping the pads off the board trying to de-solder it.
So, one thing at a time. The blinky video course on the site doesn’t seem to have the instruction to solder the board together. I thought I saw such a video on youtube and I am about to go try to look it up. I also checked the skills section, but I don’t have access to many of the courses or skills despite my account level. It shows me logged in and then when I get to the page, it tells me to purchase the correct type of account or log in. So @ChrisGammell, I was wondering if you could help me with my problem accessing content. I am currently using the latest version of Firefox. I will give Chrome a shot, but I generally try to stay off of it these days due to privacy concerns.
I have two more boards and two more 7555’s. If I mess up the next one I will look for instruction on de-soldering before I try that again. BTW, @Graeme, I used much less heat this time and it worked fine.
So now I watched the Blinky 4.0 final video and see I should have just done 1 pad to start with. So I did that and the 7555 solder was pretty straight forward otherwise. Unfortunately when I went to get the rest of my parts I realized that I never ordered the 1uF capacitor and the pack of 10000 pF capacitors I did order is nowhere to be found. It appears I will be waiting for Digikey to finish this one up.
Oh and are fantastic for applying heat-shrink tubing.
BTW,