My Homebrew ESR Meter

[Difficilus]

Hi Dana,

Sorry to hear of your hassles.

Like Joe, I've just printed off the article at the link he set up, and the PCB artwork comes out the correct size.

The image as it appears, including the white border, which allows for holes at each corner to mount the PCB, should be 5.46cms high and 8.92cms wide. (In inches, that's 2.15" high and 3.515" wide). The height and width of the actual PCB tracks on the artwork (not allowing for any border) is 5cm high and 7.5cm wide. If you are using something like Photoshop, if you do need to re-size, just set one dimension it should automatically set the other. The easiest way to check if you have the artwork the right size is to sit a 14-pin IC socket on the artwork and see if the pin spacing on the PCB is the correct size to marry up with the IC socket.

If you intend to use the 'iron on' method to apply the artwork to the PCB rather than UV exposure, (either the laser printer onto glossy magazine paper or glossy photo paper, or the 'press 'n peel method), do remember that you must 'flip' the artwork or your design will iron onto the PCB the wrong way round. The tracks on the finished PCB must look like the artwork.

As to etchants for making PCBs, I've long since abandoned messy ferric chloride in favour of Sodium Persulphate copper etchant. This is an effective alternative to ferric chloride which has a 6 – 8 minute etch time at 45C – 50C. The bath life is about 4 – 6 weeks depending on use and operating temperature. The product is supplied as a fine crystalline white powder and the instructions for use are printed on the bottle label. You mix it with warm water and it's a colourless liquid which in use, turns pale blue as it etches away the copper. You can store it for re-use till it loses its effectiveness.

I don't know how you are fixed Stateside for obtaining such chemicals - maybe you'll have the Dept of Homeland Security knocking on your door searchng for WMD!

In the UK it's easy and cheap to buy on internet:

EG: a 500 gram HDPE bottle, which will make up to 2.5 litres of etching solution costs just £3.50GBP +£2.24GBP P&P

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=270746775207&ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Best of luck with the project Dana - many have been built over the last three years or so and help is on hand if you need assistence in trouble-shooting.

Great info. The dimensions are exactly what I needed. Well, that and you and Joe's reference to the image in 40 printing correctly with no scale issues. I had no problem printing from that image either. I'd been using a cut and paste from the pdf that Joe put up on 50. I may still make some adjustments to the image with this sizing info.

Could not use the IC to check the print size as it had not arrived yet. Could have use a 5mm radial Electrolytic cap or even calipers and a rule I suppose. I'll probably do this on all my images before to make sure the image is correctly scaled before dropping the board into the etch. Nice to avoid making a rather unattractive coasters out of them.

Nearly all of the remaining components and a pair of 50uA meters from Hong Kong (whew) arrived today. I only need to decide on a suitable project box and decide which pair of test probes to grab in order to move along.

I have been researching the different etch solutions and various methods of resist and I am going to try the Laser print/iron on/wash/etch/and rinse method. I'll use the photo or glossy paper you suggest but I'm not comfortable running magazine slicks through my printer.

Like you, I've decided against ferric chloride as it appears to be bit nasty. I decided on cupric chloride for the etching solution. I have purchased 30% hydrochloric acid (muratic acid used to clean concrete and cement) from the neighborhood Ace Hardware store at about $4.79 US for a quart container, and a pint bottle of 3% hydrogen peroxide from the pharmacy/hair care department at Walmart for $.52 US. I understand that a proper mix of these two will give good results, stores well, and is reusable indefinitely with a bit of refreshing now and then.

I don't know much about Sodium Persulphate. I must say it sounds right. Easy to use, cheap price, stores well. If the cupric chloride should prove to be a disappointment I'll certainly give it a try.

I'm looking forward to putting this little beasty together and getting intimate with some bad, component killing, high ESR caps!

Thanks for all the great info and help. It's much appreciated.

Dana Locke
Missouri, USA