S6 Use prototyping techniques for testing circuits

Posted: October 10, 2010 in Systems and Control

Initial knowledge – 0

Current working knowledge  – 2

Initially I had no knowledge of using prototyping techniques for testing circuits.  In reality having done the ambiance light project I had not used any prototyping techniques to test my original circuit.  In fact rather naively I simply produced the PCB and then added the discrete components to it in relation to my PICAXE programming.  Fortunately at the time I had the circuit working but I then chose to reproduce it using new leds and the wiring lengths I needed for the actual finished product.  Of course this time I had problems downloading the circuit and having re-created it 3 times using re-manufactured PCB boards I still had issues getting the final led to light.

A technique that I had not yet discovered was the use of prototyping boards or breadboards.  In fact when asked if I had used a breadboard for the light project I thought that it was slang for an additional pcb board to which I answered no, both correct answers but completely in the wrong context!

However during my competency project, to indeed show competence I have been recreating circuits on circuit wizard and then actually making them on said breadboards to show the circuits working in a physical sense.  It is since using the breadboards I realise how beneficial they could have been in my light project.  Had I introduced the prototyping boards at the earliest opportunity then I could have got a better understanding of the way my circuit was operating.  By prototyping the circuit there is no need for the constant soldering and in my case re-soldering of components that are not working.  Instead they can be simply re-wired with the use of single core wire and placed in a different position on the breadboard without damaging the components.

I have found using this technique really useful and rewarding as not only can I make the circuits up and see them working, I can also re-make them when they are not without causing damage and get a better understanding of where I went wrong.  I find the layout of the breadboard easier to understand than a pcb board so it is certainly beneficial in a visual sense.  Buy using appropriately coloured wires  I am able to see the electricity travelling from the positive  output of the power pack to a component and then its journey onward to reach ground in a clearer way than if there is a lot of wires travelling to different components in an incoherent manner.

Another benefit of using the breadboards is that I find it easier to engage with the different components themselves.  By having the circuit laid out in a methodical manner you can see where the electricity reaches a component for instance a capacitor and using the multimeter it is possible to see the electrical charge build up within the capacitor before it is released to a component such as an led.  Of course this is useful if a circuit is not working as individual components can be analysed and tested and again I think because of the layout of the board it is easier to do it in an methodical manner , for example by starting on the top left and working across the board until each part of the circuit has been tested and the fault found.

Connections on Breadboard

Breadboards have many tiny sockets (called ‘holes’) arranged on a 0.1″ grid. The leads of most components can be pushed straight into the holes. ICs are inserted across the central gap with their notch or dot to the left.

Wire links can be made with single-core plastic-coated wire of 0.6mm diameter (the standard size). Stranded wire is not suitable because it will crumple when pushed into a hole and it may damage the board if strands break off.

The diagram shows how the breadboard holes are connected: Connections on breadboard

The top and bottom rows are linked horizontally all the way across as shown by the red and black lines on the diagram. The power supply is connected to these rows, + at the top and 0V (zero volts) at the bottom.

The other holes are linked vertically in blocks of 5 with no link across the centre as shown by the blue lines on the diagram. Notice how there are separate blocks of connections to each pin of ICs.

On larger breadboards there may be a break halfway along the top and bottom power supply rows.  It is a good idea to link across the gap before you start to build a circuit, otherwise it might be easy to forget and part of the circuit will have no power.

http://www.kpsec.freeuk.com/breadb.htm

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