Prototyping

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So what is the best way for prototyping a circuit;

You have several options:

Solderless bread board.
Stripboard.
PCB using press & peel (laser printer or photocopier required).
PCB.

Jump to Prototyping wire recommendation.

Using a Solderless breadboard

A solderless breadboard (or solderless circuit board) has an array of holes on top and enclosed connections underneath. You can plug any standard sized component into the breadboard e.g. an IC or solid core wire.

Typically each row is split into sets of five connections that are joined together underneath and for each connection there is a spring grabber that grabs whatever wire is pushed into the top.

Usually around the outside edges rows are connected together and columns are connected together - these are intended for supplying power to each IC i.e. a convenient place to get 5V or 0V connections. In the diagram below the left column has been used to give access to the zero volt connection (green wires).

So you can use them to quickly make up a circuit by plugging in an IC, LED, transistor and then routing all the connections using solid core wire (with pvc sheath).

Note: If you have a small circuit to test or develop they are ideal as they let you quickly change and add components.

Warning :

They are only useful for up to the minute development. Never use them for a permanent circuit because once your back is turned or its been put to one side a wire will be knocked out and you'll spend ages trying to find out which one. This problem is made worse the bigger the solderless breadboard and the one shown below is one of the smallest).

Only use them for testing non critical circuits - they are ideal for digital circuitry but not so good for analogue as you have no control over the ground routing path, stray capacitance etc. and never use them for RF.

Here is a graphical example of using a solderless breadboard for prototyping.

Click here to see the schematic for this solderless breadboard.

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Prototyping using Stripboard

As its name suggests stripboard is a board made up of strips - strips of copper track with pre-drilled holes. To make up circuits you solder components into the stripboard and use a track cutter to cut tracks between components and make connections by soldering components e.g. resistors or wire links between tracks.

If you are careful you can often design a simple curcuit without using too many wire links but if you are designing a bus based system (e.g. 8 bit bus) you quickly need to add many wires.

If you are using a processor circuit you will need to make many track cuts and I would suggest using a strip board that has tracks broken into sets of three. This lets you place components and then wire up using prototype wire. Some boards also have power connections specially for placing ICs e.g. Euroboard - these don't have the best grounding path but they are useful and work well for prototypes.

Wire for prototyping

The first thought is to use the solid core wire that you used on the solderless breadboard but this is the most difficult wire to use as the PVC sheath has a low melting point. You quickly find out that if you hold the soldering iron on the wire too long the pvc sheath melts and exposes the wire underneath.

For prototyping I'd recommend using wire wrap wire or another wire with a high melting point sheath. The reason is that during prototyping you will often change the circuit - the wire wrap wire (Kynar wire is similar) will let you re-solder it lots of times and will not melt.

The only trouble with it is stripping the wire wrap wire - you can buy a tool at about $40 but I use ordinary wire cutters to only just cut the sheath and pull that bit off exposing the wire. OK so sometimes you cut a little too far and break or weaken the wire but with practice this technique works and once you have placed the wire you can move it by melting the solder and removing the wire.

This method gives you a permanent circuit that is reliable and suitable for one-off development.

However you will soon get tired of it especially if there are lots of wire connections so the next option is to make a PCB.

PCB Prototyping

Making a Press n Peel PCB for prototyping

Your best option for making your own pcb is to use a single sided board with Press n peel technology. This lets you make a PCB using a laserjet printer or photocopy that prints directly onto the Press n Peel paper.

First you print a reverse image onto the PnP paper.

Then all you do is iron (using your normal domestic clothes iron) the PnP paper onto a copper clad board.

Wait a while then peel off the Press n Peel. This leaves the printed pcb pattern on the copper board ready for etching in the normal way.

Note: You can use this method to easily and quickly make single sided boards but you still have to use the standard 'nasty' chemicals'.

Making a PCB for prototyping

The only difference between this method and the Press n Peel method is that you need a UV lightbox and UV sensitive copper clad board.

To make the etch resist you expose the board to UV light with a transparency of the pattern to etch in front of the board. Exposing the board to UV light chemically changes the exposed areas of the board and you can etch these area away using chemicals leaving the copper tracks making up the PCB.

Problems with making your own PCBs.

For prototyping a single sided board these methods are fine.

If you create a double sided board,which you will need to do as you create more complex circuits, then there are no through hole connections. And aligning the top and bottom etch resist masks is a difficult task.

In a manufactured PCB through holes connect on side of the board to the other using a plated through hole and these plated through holes appear anywhere you use a leaded component e.g. an IC. This means you don't have to think how to reach the other side of the board as you do if you make your own PCB.

Another problem is that you won't have a silk screen (usually white text) to identify where you place components - this becomes essential for more complex boards. And if you need to come back to the project at a later stage you won't remember where all the components are unless you have kept very good documentation.

Making your own prototyping boards is useful but only for one-off designs and the best way of doing it is to use Press n Peel for single sided boards.

Note: You should be certain of your design as it generally takes several iterations to get it right.

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