555 LED Flasher to a PCB - First time - Keeping it simple. - Page 1
Forum section: electronics / projects

author: Philbywhizz
author_rank: Contributor
timestamp: December 19, 2014, 11:50:25 pm
content: Hello,I'm recently rediscovering my old passion of electronics (and thanks to sites like EEVBlog)In the past (1990s) I had just played with electronics with breadboards and non-soldering (Dick Smith Funway 1 & 2 - I still have the books) I really wanted to move from breadboarding to something more permanent and while I could just use prototype board (one with just pads) I found it can get a little messy.So for the first time I went down the 'design a pcb' path. You can read about it in more detailhereon my blog if you want. Rather than going all complex, I just kept it simple with a known circuit - I think of it as my 'Hello world' to creating pcbs.After about 3 weeks I received my first ever self-designed PCB board from OSHPark. And I'm excited!!! (I feel like Dave with one his mailbag blogs).The final product:I'm actually quite pleased from the result - I haven't soldered the components in yet (that will be the final test that I've done everything all ok) and I'm sure many experts on here will point out mistakes on my layout. Please go easy - It's my first one.I highly encourage new beginners to give it a go and design your own pcb board - move from a prototype board to a pcb board - it is actually quite fun, the learning slope is a little high, but the rewards are awesome - (and I'm getting such an awesome buzz right now - if it wasn't for Christmas shopping that I have to do right now I'll be soldering this thing!!).Cheers,Phil.(Philbywhizz)

author: tinytim
author_rank: Contributor
timestamp: December 20, 2014, 01:27:08 am
content: Hi PhilLooks good. Always great to see some enthusiasm coming back into the hobby.Whats your next board revision, 1206 smd ?? Gotta be worth a go

author: Philbywhizz
author_rank: Contributor
timestamp: December 20, 2014, 01:55:39 am
content: Quote from: tinytim on December 20, 2014, 01:27:08 amI'm not sure about using smd components though, it "seems a bit too hard" - but then again if you asked me 2 months ago if I would design my own pcb and I would have said "seems a bit too hard". I also find through-hole components are far easier to collect and salvage with the basic tools and equipment I have.But having a pcb board manufactured like this certainly opens up many possibilities that I didn't think was possible for a hobby.

author: Zero999
author_rank: Super Contributor
timestamp: December 20, 2014, 11:38:12 am
content: The circuit on your blog contains a few errors.http://i2.wp.com/www.philbywhizz.com/wp-content/uploads/2014/11/schematic.pngCompare it to the correct schematic on the datasheet and you'll see what I mean.http://www.ti.com/lit/ds/symlink/ne555.pdf(page 11)

author: Philbywhizz
author_rank: Contributor
timestamp: December 20, 2014, 11:25:45 pm
content: Quote from: Hero999 on December 20, 2014, 11:38:12 amFirstly, thankyou for taking to time to look at my little project. When I saw your message telling me there was some errors I have to admit I was a little sad. But rather than get upset about it what it did was made me did a little deeper - WHY? (I even got out my oscilloscope - which i'm still learning how to use). Did I miscount the pins on the 5 timer the wrong way? Did I just show the whole internet what a goose I am?What made it more confusing is that I currently have this circuit up and running on a breadboard and it is flashing. This is what I based mycircuit on. I had modified this circuit slightly by putting a resistor between pins 2 and 6. It is different to the circuit in the pdf datasheet. Perhaps this it isn't the proper way to make flashing LED's with a 555 timer but it seems to be working in this case.But I want to know why does it still work? I'm taking a self-educated stab here and guessing that the output pin (3) on the 555 is making pin (6) go high and low (like a crude feedback loop) as it oscillates. Now that I'm looking at it in more detail I do notice that the first light is on for a little but longer, then it flashes (initial charge up of C1?) Did I just get lucky with why this still works?So perhaps my pcb will still work - just not the ideal way. At the end of the day, my goal of this little project was take something on paper (a schematic) and go through the actual workflow on how to get to the pcb stage and solder it up as a 'finished product'. I'm still quite happy with this that I achieved this goal, and on the side I've also learnt a lot more about 555 timers by doing so.So I went from being sad to back to happy again - with a new appreciation on the efforts people go through when they make/design their own pcbs.Now I think I understand when people say 'failure is good' (I don't feel like I've failed though).

author: Zero999
author_rank: Super Contributor
timestamp: December 21, 2014, 01:00:36 am
content: Quote from: Philbywhizz on December 20, 2014, 11:25:45 pmYes the circuit you linked to will work. It may not be as per the datasheet but it does work. I've built it before. The 555 timer is used as a Schmitt trigger and the capacitor is charged and discharge via the same resistor. It has the advantage of saving a resistor and if you use a CMOS 555, the output 50%The circuit you showed in your blog doesn't work. The capacitor is just connected to +V via R1 and R2. It'll charge up but there's nothing to discharge it.I doubt you used that circuit. Perhaps you've posted an earlier version on your blog?In the 555 circuit on the datasheet, pin 7 discharges the capacitor. It can also be discharged via pin 3 but you need to be aware of the fact that the bipolar 555's output stage isn't symmetrical and the stability will suffer somewhat. The CMOS 555 (7555/TS555) is better but you mustn't draw much current from the output.See links below for more information:http://www.williamson-labs.com/555-tutorial.htmhttp://www.electronics-tutorials.ws/waveforms/555_oscillator.html

author: Philbywhizz
author_rank: Contributor
timestamp: December 21, 2014, 02:21:05 am
content: Quote from: Hero999 on December 21, 2014, 01:00:36 amAgain, you are correct - after looking at it in more detail the layout on my breadboard circuit doesn't match my schematic (it matches the one from the 555-timer site though).I've since rebuilt my schematic on a different breadboard (so I could compare the two) and the 2nd one does exactly as you describe - LED1 lights up, 2nd one then lights up but then doesn't flick back to the first. I've also soldered the components onto the pcb and it does exactly the same as the 'failed' schematic (and 2nd breadboard).I must have adjusted the original breadboard circuit while experimenting and building the original circuit, and translated it to Eagle incorrectly. I was too focused on making sure that the pcb layout matched the schematic, but didn't make sure the schematic was correct to the breadboard layout.I guess that highlights that you have to get the 1st step correct, otherwise it cascades into errors down the workflow.What I am pleased with though is that while the schematic is a big fail - the circuit design on the pcb works 'as per the schematic' - which gives me a bit of confidence that 'I can do this' the next time i desgin a pcb (A good start might be to re-do this with a correct schematic)Thanks again for the detailed explanation - I'm really glad I found this forum - it just encourages me to keep going.

author: Zero999
author_rank: Super Contributor
timestamp: December 21, 2014, 11:18:49 am
content: All is not lost.You could try modifying the PCB with bodge wires: unsolder +V side of R2 and connect it to pin 3 (via R3 or R4 is good) and it should work.Making modifications to PCBs is a good skill to have.

author: Philbywhizz
author_rank: Contributor
timestamp: December 21, 2014, 12:25:17 pm
content: Quote from: Hero999 on December 21, 2014, 11:18:49 amGood point - I never thought of doing that - I have so much still to learn.

author: rob77
author_rank: Super Contributor
timestamp: December 21, 2014, 10:11:26 pm
content: Quote from: Philbywhizz on December 20, 2014, 01:55:39 am1206 SMDs are pretty comfortable to work with, i would encourage every hobbyist to use them. even toner transfer method for PCB making is good enough for 1206 SMDs and quad flats.