555 IC Project - 'Red Alert' Siren query.

[Mark Hennessy]

Good news! I wonder why the original designer mentioned in the original post didn't get it working?

Of course, those sounders contain drive circuitry, so it'll be interesting to hear what they make of being driven by your two 555s

As they only take 15mA, the 555 can drive them directly. As the existing circuit appears to be dumping the best part of 100mA into the base of the 2N3055, that'll be a useful saving.

(Of course, as you've built the board - and I imagine the giant 2N3055 looks pretty sexy on there - you might not want to start modifying it. In which case, you could simply increase the value of R6. Something in the 1 to 10k region would probably provide enough current to saturate it when driving that sounder)

Pictures please

[Yorkie]

Thanks for that useful additional info Mark.

Can't answer the other points - I didn't build it myself - I just designed and etched the PCB for a chum who then built it, having originally built it (unsuccessfully) on strip-board.

I'll pass on the info about the piezo sounder having its own driver.

Amazing the breadth of uses to which 555s can be put which go far beyond timers and sound generators - a mountain of stuff on the net about them, including on youtube (stepper motor/servo/DC motor controllers etc). Despite their oft mentioned vices and limitations, it's easy to see why it's still in use several decades after it made its first appearance.

I guess that these days, to many experimenters 555s yesterdays news, with PICs, Arduino etc coming more to the fore, but for simple souls like me...

[Yorkie]

Pictures please

I'm informed that the PCB is finished and working fine, along with the timer 555 based unit mentioned in an ealier thread.

Pic of the 'siren' PCB attached below as requested.

Thanks once more for the help and encouragement!

[Mark Hennessy]

Very nice! Can't beat a PCB, even for one-offs. I used to make them all the time in the past - I'd have designs on the go to slip in along with the prototypes that were required at work. At the moment, what with the kids and various pets, I've decided to not attempt to do them at home - especially now that the prices for professionally produced PCBs have fallen so dramatically. Maybe later - I do miss the process...

[Aerodyne]

Entirely endorse your view on PCBs, Mark. I make my own and have done for many years. Easy at work, where the facilities were handy but in my retirement years I use the sun, clear inkjet film and the utility room sink! No problem at all. Why people have bother with inkjet prints when making PCB track patterns puzzles me. I have a standard - basic, really - Canon MP560 scanner/printer and make two high quality copies on clear film, transposing one on top of the other to gain sufficient density.
Agree too about the dangers relevant to kids and pets...
Tony

[Mark Hennessy]

Thanks, Tony

I had good results with an old laser printer (found in a skip, repaired and used for several years until the toner ran out!). Like you, I did two prints; it worked really very well. Having said that, modern laser printers are generally much less "dense" than this old beast, so it's likely that inkjets would do an equal or better job. My old Canon MP800 printer/scanner has two black ink tanks - one is dye and the other is pigment - and I wonder if the pigment-based ink would offer better opacity to the UV? An experiment for the future...

I've seen some interesting designs for UV light boxes that use UV LEDs rather than tubes. But using the sun is a great idea!

When I worked for a company that had the in-house facilities, we used a photographic method to transfer the artwork from a laser-printed master (just on plain paper) to a transparency. I remember their "darkroom" was a tiny cupboard under the stairs - happy days! It produced very dense artwork indeed - arguably more dense that was needed, but at least it meant that the timing of the UV exposure wasn't as critical. It was also good for backlit front panels and similar projects. From there, the next cupboard housed the standard RS tanks, along with an old Belfast sink. It was a satisfying process, and made a nice change from being stuck on the bench...

There is another possibility - PCB milling machines. For many years now, I've been patiently waiting for the price to become affordable, but no sign yet. Perhaps the coming of 3D printing will help, as most of the parts are shared? These really appeal to me because they also do the drilling - which is the part I always enjoyed least! The number of times I missed a hole, or didn't drill it out to the right size, and didn't spot this until I'd partially populated the PCB... But of course, it does produce PCBs that look different to normal - you do tend to leave a lot more copper on the PCB (not necessarily a bad thing).

Overall, making PCBs is good fun. Even if you're just doing the artwork to send out, there is a lot of "art" involved - especially if you're sticking to single-side and are trying to minimise board area while keeping the number of jumper links to a minimum. But, with care and planning, Veroboard can be pretty reasonable - certainly for audio frequencies. There are compromises, of course, but that's life

[Nick]

Some PCBs can be works of art - see the enclosed from one of our nixie clock designers

I no longer make my own PCBs - its messy & uses nasty chemicals that can't be got rid of easily.

[Yorkie]

I bimble along as I have for decades now, making my own PCBs in my own way. I guess if I were starting out today, I'd give the 'iron on' laser print process a go as it cuts out a lot of the stages as compared to UV, but I'm in a rut as deep as a grave

I know that those further up the food chain than me (a lot further!), simply send a Gerber file to a PCB pool, and get a highly professional board for not much more than all the DIY faffing about, but I don't have  the abiltiy or inclination to get into 'proper' PCB design. I don't use any PCB  drafting programs - never got into them and I'm not keen on some aspects of the output I see - leastways, not for DIY etching and drilling. The tracks seem too thin and the pads needlessly small, so if I see a design I want to use, I tend to 'beef up' the tracks and pads in Phtoshop or Paint. I try to have the tracks and pads reasonably wide, to allow for any undercutting which can occur when exposing and etching a board.

Until late 2010 I had an aging HP printer which had a transparency setting and produced splendid solid print on acetates, but the printer died on me. I bought a well recommended Epson at the time, assuming it would produce as good if not better results on acetate, but I later found that no Epson printers support acetate printing. Maybe it's because OHPs have largely been superseded by Powerpoint presentations and digital projectors?  Mostly, so long as it's not a complex PCB, I can get by if I tape two or three copies over each other. I don't use pre-sensitised boards - I spray my own, then if the process fails, I can just wipe the board clean with Meths and re-spray with UV lacquer.

Joe Freeman (formerly of this Parish),  pointed me to a youtube  video by a chap called 'Big Clive' who suggests how to alter the settings on Epson printers to get more solid print  for PCB masks by changing the settings for saturation, density, contrast, colour and brightness to maximum, and to use the 'Epson Matte' paper  setting. which I was hopeful about. I've tried that and it has produced a marginal improvement, but  I've also tried a new type of film from Crafty Computer Papers for printing the artwork onto called 'micro porous film':

http://www.craftycomputerpaper.co.uk/.-M..._S048A.htm

Definitely better than  normal OHP film on my Epson. The normal OHP film I've been using is much cheaper - presently £15.00 for 50 sheets:

http://www.amazon.co.uk/INKJET-CLEAR-PRI...B000KJO7BO

Big Clive's video about making photo resist PCBs with an Epson ink-jet is at the link below. He rambles on at length, but explians how to set the printer up at about the fourteen - 20 minute mark:

See: https://www.youtube.com/watch?v=W_oDBp_wgJQ.

I'm presently trying to produce a couple of PCBs for the 'mini mod' using the artwork kindly supplied by Ian Liston Smith, the mini-mod designer.  Ian used a ground plane, which I don't think is really needed for something working at MW frequencies, but I've stuck to the design and have retained the ground -lane though I've tweaked the artwork, increasing the clearance from the tracks to the ground-plane, and have increased the size of the pads where it's possible to do so. I've had one attempt at etching the PCB, but it's not really to my liking, so I'll have another go. I've attached a pic of the exposed board, when etched. Not up to scratch and certainly way below  professional standards. I try to aim for high skill, low tech and this effort doesn't meet the first criteria!

No sense to it of course, in terms of time and effort, when a commercially produced board - certainly a batch of boards, would probably cost less than the materials, but it's a hobby, isn't it?

As to UV exposure units, I made mine many years ago, but I'm very impressed with the one designed by Joe Farr at this link:

http://www.hobbyelectronics.net/con_uv-e...-unit.html

It uses 100 high brightness UV LEDs, which can be had for £3.00 post free at the link below. Yes, that's not a typo - 3 pence each!

http://www.ebay.co.uk/itm/100-pcs-3mm-2-...0011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D29271%26meid%3Dffa5459f77764cc487f81a75dc1086fb%26pid%3D100011%26rk%3D6%26rkt%3D10%26sd%3D270984675905&autorefresh=true

100 resistors for £1.00 and a piece of stripboard - total cost not much more than a tenner!

I’ve long since abandoned using ghastly ferric chloride as an etchant, both on cost grounds, and as it’s so messy. It’s only merit is that it lasts quite a long time in solution.

Instead, I use Sodium Persulphate clear PCB etchant. This is a much cleaner effective alternative to ferric chloride and has a 6 – 8 minute etch time at 45C – 50C. (above 50C it loses its strength).  The bath life is a maximum of 4 – 6 weeks depending on use and operating temperature. Unlike ferric chloride, it leaves no residue – the solution turns pale blue in use. I warm it up with an aquarium heater and check with an infra-red thermometer, but you can stand the plastic etchant container in a washing up bowl of boiling water to warm up the etchant. You can use it cold – it just takes longer to work.

As the PCB etches, the liquid turns light blue and you can see through it to check etching progress, unlike Ferric Chloride. You can use it several times over. I use an aquarium heater to warm it up, and an aquarium air stone about 4” long, with a small aquarium air pump, placed in the bottom of a plastic cereal container to ‘bubble’ the solution to speed up the etching process, but you don’t have to.

I get Sodium Persulphate 1KG plastic bottles from a reputable hobby chemicals source, currently £13.99 a kG, which will make up to 5 Litres of etchant:

http://www.ebay.co.uk/itm/221237579788?_...2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

First pic below is of the mini mod PCB after exposure and developing. I've tweaked the original artwork of the ground-plane to give a bit more clearance around the tracks, and slightly increased the pad sizes. Second pic is the PCB etched, before it went in the bin - just not up to par. It evokes memories of schooldays - "tries hard, could do better". Quite so.

More another time.

[Nick]

I've met "Big Clive" (aka Clive Mitchell).

He's quite scary (not really true). Made some other videos too which probably aren't appropriate for this forum... (as a moderator, if I posted one I'd probably have to ban myself   )

He's very active in the HV world that I used to inhabit, and is also, famously, the genuine certified inventor of the circuit we all know as the "Joule Thief", to the extent that he coined the name as well...

The Joule Thief was based on a circuit published in the Ingenuity Unlimited section of EPE in November 1999 by a chap from Swindon called "Z. Kaparnik" - Clive developed it, gave it the name we all know, and published it.

The only reason I know this drivel is that many years ago I re-wrote major chunks of the Wikipedia entry on the Joule Thief   (because the previous entry was rubbish and plain incorrect)

[Aerodyne]

This thread has deviated rather but is following an interesting path. As far as LED PCB exposure units go, I designed and made one four or five years back and sent it for publication in EPE. It was accepted but never saw print. I still use it from time to time but sunlight is less trouble! I too used my laser printer (until it finally gave up the ghost) and I used the same method as I practiced with the students at school, printing at high density on plain paper then 'translucentising' the paper with a quick spray of WD40 (on the back, not the print side or runs occur). This made a very satisfactory and essentially cheap mask for PCBs.
I still use ferric Chloride. It is cheap and messy, so care is needed.
I have two Canon inkjet printers, both support transparencies. However they are getting old, like their owner!

Regards
Tony