Quickie PCB Production (with Bonus NiCd Battery Charger)

There's a lot of very good resources on Instructables for doing laser printer toner transfer, and for complicated circuits or fine-pitch work it's probably the way to go.

But what if you're stranded on a desert island with no laser printer and you still want to work out a super-quick printed circuit? What then?

(OK, honestly, I just find it a bit of a hassle to fire up Eagle, etc just to make a quick and dirty battery-charger circuit.)

Here's a start-to-finish home-etching-with-Sharpies mini-tutorial. It's basically "draw the circuit with sharpies, then etch" but the gold is in the details.

Step 1: Stuff You'll Need

From blank copper-clad board to working prototype:

Copper clad board
Ruler and matte knife to cut it
Scrubby pad to shine it

Three (3!) Kinds of Sharpie: Ultra-Fine, Fine (Regular), Chisel-Tip (Wide)
An empty piece of protoboard (the secret ingredient)
Etchant

Drill and bit
Components
Soldering Iron

Pen and paper for working out the circuit layout

Comments

[simplebotics]

What reusable etching solution were you using. Currently I used ferric chloride.

[The Real Elliot]

Ferric's great, and simple.

I actually use a homemade etchant that I'd recommend for the long run: http://www.instructables.com/id/Stop-using-Ferric-Chloride-etchant!--A-better-etc/

Oh, and tthe shirt-folder bot is awesome!  I'm going to have to make one for my girlfriend.

[simplebotics]

Nice robot walker!

[hosam_eldin]

nice work, but you should monitor the battery temperature to avoid over charge wait for my Instructable for a PC based smart charger

[tytower]

I'm surprised at this The more usual charge for 850mAh rechargeables would be about 85mA for 10 hours . At 600 mA odd the life of the battery would surely be reduced markedly wouldn't it ? Guy above says nice work and he is going to do one too . Will I wait for that ? Don't think so.

[The Real Elliot]

It's true that there are tons of chargers that charge at 1/10 C (85mA for an 850mAh battery) over 10 hours, and these are mostly the cheapest, simplest chargers. The reason for using such a low current is safety -- even if you leave it on the charger forever, it probably won't vent or blow up. Overcharging is _not_ good for the battery, but at least it's not a safety hazard.

According to
http://batteryuniversity.com/learn/article/ultra_fast_chargers, 1C (for a roughly one-hour charge from empty) is a "gentle" rate. According to the wikipedia article on NiCd's, 1C is the standard fast-charge rate. I've charged and discharged old NiMH phone batteries hundreds of times at 1C with no noticeable ill effects. My drill's battery charger gives 5C to the cells (15-min charge), and they worked for five or six years before I had to replace them.

What you _don't_ want to do is overcharge. And charging faster makes that easier to do. So if you use this charger at 1C, set yourself a timer and check on it again at 1/2 hour if you're not sure that the battery was fully discharged to begin with. Be conservative -- a NiCd or NiMH battery lasts longest when neither fully charged (avoid overcharge) nor fully discharged (which is bad for NiMH).

And of course, the best thing to do is get a smart charger that ends the charge by time, temperature, and/or voltage. But in that case, there's even less reason to avoid charging at full speed.

And _do_ note that none of this goes for lithium batteries, which want a totally different charging schedule.

[The Real Elliot]

Agreed. One absolutely should monitor temperature increase (or the slight voltage drop that NiCds get) when they're at 100%. This was just a quickie to get a bunch of batteries up to working levels pretty fast. And as I was doing it, I thought to myself that the only other tutorial on hand-drawn sharpie PCBs was one with non-standard pin-spacings. So... Someday, I may get motivated to make a proper voltage-drop-based charger. (I got some ideas.) Probably not until I leave this one one and fry a few batteries, though. Love to see your charger design. Feel free to post up in the comments here when you get yours running.

[tytower]

I'm surprised at this The more usual charge for 850mAh rechargeables would be about 85mA for 10 hours . At 600 mA odd the life of the battery would surely be reduced markedly wouldn't it ? Guy above says nice work and he is going to do one too . Will I wait for that ? Don't think so.

[Jugfet]

With the 317, as with most V regs, it's best to keep the input voltage as low as possible and then the chip will not generate as much heat.
If for instance you want 6V out - that would be 6Volts + 2.5V offset so 9 volts would be good 12 volts would probably be more practical 18Volts and your heat will be much higher making an overall less efficient circuit.

[Unit042]

I have been using the battery charger circuit here for a while. A variable constant current supply is quite handy.
Anyway, the PCB techniques you present here are excellent ideas, thank you for taking the time to post them online so the rest of us can learn from it.
I am impressed by your creative use of perfboard, both in marking and especially drilling. I was half expecting you to say "okay, now guess at where you thought the pins were," but no, you give us a very good tactic instead.

I may not do PCBs by hand anytime soon, but now I am armed with a proven plan of attack when the need arises. Hooray for The Real Elliot! :)

[amando96]

you sir are awsome, i'm making a barebone arduino board with this, will i regret it?

also dude down there `´ `´ dont drill it, cut the pins off and solder like they are smd's, takes some practice, but driling is a pain without the proper tools

[raykholo]

you use a hand drill for the holes? what size bit? i ve heard that the tugsten carbide bits will break unless used with a drill press. So if ur using like standard 1/16 in. bits (not made specially for pcb use) then is it still possible for those big holes to accommodate the component leads? ... yeah, its a lot of questions but i like your method and am trying to be able to do this on the cheap ( i dont want to buy a drill press...) :) thanks

[The Real Elliot]

I use PCB bits, the small ones. I've never broken one, but they do seem a bit fragile. I bought 3 on sale from All Electronics or Electronics Goldmine ages ago. Sometimes, if I'm freehanding it, I'll steady the drill on my leg to make it kinda like a press. (You'd have to see it.) Using the protoboard as a drilling jig probably also helps a lot.

[raykholo]

so those 2 sites are ones that i use so that helps and i can just add the bits in my next order... the perfboard jig idea is pretty clever the pcb bits u use seem to be tugsten carbide and i was just wondering about using them freehand... other methods i have read advise using them with a drill press at 2000+ rpm otherwise they risk breaking so nice to know thats not exactly true and thanks 4 answering that thanks again and any other advice u got 4 someone just getting started with this stuff would be great... im good at electronics... just havent worked with pcbs yet...

[The Real Elliot]

Update:  I bought some super-tiny carbide drill bits and discovered that they are brittle after all.  Be careful not to apply much side-force to them when drilling.  At least they're only $1 each from the surplus guys.  But, buy a few more than you need. 

The non-fragile bits I have been using look like regular 1/16" bits, but read 0.039" in the calipers (5/128"?!?).  They seem to be stronger than the carbide ones, and are a good size for DIY holes. 

Or skip the drilling and the mirror-imaging entirely, and do everything top-mount.  (I smell another instructable coming...)

[crazyromanian]

The Real Elliot, where did you buy the etchant? thx.

[twenglish1]

this is awesome i just made something today using this method and it works great and i also used your etchant (5 stars)

[osgeld]

the 317 wont burn out, it should be limiting current to prevent it also that might be enough of a heat sink, ive used alligator clips and pulled an amp but they are solid metal and not just a foil coating

[The Real Elliot]

Yeah. I've been using this very charger since I posted it up, and it's going strong. The "heatsink" gets pretty hot, which I take to be a good sign. I've started putting it in the outflow from my power supply's fan for extra cooling power. It also does double-duty as a LED tester/meter. Put a 100 ohm resistor in it and sources ~12.3mA which is good for most low-power LEDs. You can then measure the voltage that the LED needs to light up. Handy. Everyone needs an adjustable constant-current source! :)

[osgeld]

warm = good
hot = might as well not really be there because its saturated with heat

for a heat sink to really work it has to dissipate more heat than its absorbing, that way its wicking the heat away into air

try replacing that copper pcb with a flattened down "slot cover" from the back of a pc and see if you notice any difference, i bet you will :)

[osgeld]

btw ... if you use one that has some sort of "paint" on it sand it down to bare metal first, where it contacts the regulator (use a faint amount of compound of your choice too, the silver stuff is mine ) this goes for anodized parts and plated parts!

[andy60]

excellent idea, bravo! lol

[Myself]

In the schematic presented, I don't see the big bank of resistors. What am I missing?

[The Real Elliot]

It's not overly clear in the schematic, but the parallel resistors (or at least the headers for plugging them into) take the place of "R1" and "Rv" in the original circuit diagram, or the one just labelled "R" in my quick sketch with components. That is, there's only one ( thevenin equivalent ) resistor in the whole dang design. In the one from the web, it's a resistor + variable resistor combo. In my design, it's a bunch of resistors all parallelled for a) lower resistance (higher current) and b) greater wattage handling.