One off cct board creation

[Rick Hughes]

It's been about 20 years since I did anything significant in the way of a cct board manufacture, other than one or two components on off cuts of veroboard.

I have a small project where I will be interfacing 18 mains AC signals to a capacitor voltage drop cct to have an LED indicator for state of the mains (multi zone heating system)

Decided on the cct components, have tested via Breadboard and all works fine ... I have the component and some 'solder in place' connector terminals for the mains signals. (not very complex ... it's this x 18 using common N rail )

Now in the past I have used Vero board and just drawn it out on graph paper, and then after a few attempts at layout on paper have created a board.

In this case I would need to start with reasonably neat even spacing of the LED's as they will have to 'poke' thru a plastic box lid, and then work components & connectors to suit.

Obviously since my last creation PC's and software abound, is there any good free PC layout software for veroboard ? ... or is there a neater/better/simpler way to do this one off board. It would seem uneconomic to create a pcb due to cost of etching materials.

[Andy Burns]

Dunno how small you'd want to squeeze it, the smallest (100x100mm) board that PCBpool do is about 25 euro for a one-off, maybe more realistic to say 200x100mm and have two rows of nine LEDs?

[Scott M]

I've not found a good veroboard tool. I've taken to using ExpressPCB[1] and drawing one side of the board with a load of tracks at 0.1" and put the components on the other thus separating them for easier editing.

Also, he said poking his nose in, you could simplify your circuit by losing the full wave rectifier; it's overkill, just needs a single diode to prevent the LED seeing a huge reverse voltage. Not sure the cap's really needed with the right sized resistor (I make it 18k based on a Vpk of 325v.)

[1] Half of a suite of PCB creation tools offered by some (probably US) company who'll make the boards for you. The other half lefts you draw out the schematic and then transfers the node connections to the PCB tool so you can check they fall in the right place. Free and pretty neat.

[Capitol]

Use 2 x 9K as many resistors only rated for 200V. I've seen 4 x 4k7 used to guarantee protection from mains transients.

[dennis]

It is only a guarantee if you know they always fail open circuit.

[Rick Hughes]

You said use ExpressPCB ... but how are you pysically creating the board ? ... I don't have any etch chemicals ... long time since I had Ferric Chloride in my garage.

I did try simpler 1/2 wave rectification there was distinct flicker at 50Hz. The cost of Bridge rectifiers were only 14p each, so no big issue.

I did consider using just a resistor but if you are reliant on an the Voltage drop across with an in-line resistor the heat dissipated is too high ... esp as 18 could bee doing this at same time.

[Rick Hughes]

Is PCBpool a company that does one-off boards ?

I don't need it to be particularly small... 200 x 100 certainly no issue for me.

[Rick Hughes]

No thanks, as explained don't want a bank of mini electric fires.

[Rick Hughes]

where is this free tool ? any clues

[meow2222]

220 ohms is going to permit around 1.5A at switchon time - way too high. Also you need 2x 0.3w resistors to get 400v rating, unless you're using power Rs.

Print onto acetate, tape acetate to photo-etch board, expose to sun for 20-30 mins. For etching, value vinegar is very cheap, I've not tried it with photoetch boards though, perhaps try a scrap in it. Some other acids are also cheap, like citric ~40p.

NT

[Roger Mills]

Wouldn't it be easier to use mains voltage neons? Here's one example - but they come in various colours.

[Andy Burns]

Yes, their prototype service, they've muck it in with several other jobs, ty Eagle or RS's DesignSpark to layout the PCB

[Rick Hughes]

I may even leave resistor out all together ... doesn't need to be there to work.

[meow2222]

bye bye LED

[fred]

In article , Rick Hughes writes

Take a close look at the Ifsm (surge current) ratings of the LEDs, you're already looking at 1.5A pk worst case on switch on (just sayin ;-).

First thought is that 220R is a bit light.

Technically you can find the cap charged one way and a contact bounce resulting in the next connection being a polarity reversal so twice the expected current and voltage on components (laser trimmed metal film res particularly vulnerable to surge).

Some repetitive switching testing sounds like it wouldn't go amiss.

No egg sucking instruction intended or to be inferred . . . .

[Scott M]

I mean I use ExpressPCB to design a veroboard layout. It does double sided boards so I draw a grid of tracks on one side to give me a guide and lay the components onto the other side. It's not ideal, track breaks are a bit of a pain, but the veroboard tools I've tried are worse!

[Scott M]

[The Natural Philosopher]

shove an inductor in?

[Rick Hughes]

Works fine without it ... just did current measurement exactly the same DC current thru LED 31.8mA

[Rick Hughes]

used those before ... but panel would get ugly with 18 of them

I have ordered the caps & LED's now anyway