Diary of a Trainee Electronics Engineer: October 2016

Transmission mechanisms, BCS OSSG Student Competition and further debugging RC2014.

This month things have been pretty hectic: work from my HND has being coming in fast and furious and it feels like I have assignments coming at me left, right and centre. One of the big assignments I’ve been working on is to do with two port networks and determining their Norton and Thévenin equivalent circuits, which is the kind of thing I love doing, as it involves quite a lot of equations and calculations.

In the unit, Further Analytical Methods, I’ve managed to rattle through a couple of assignments this month, the latest of which was converting between binary, decimal, hexadecimal and octal. I’ve really enjoyed this unit to date, not only because it’s very mathematics orientated but because I can see how this will be applied to the sort of work that I’m currently doing.

In another module we have been learning about amplifier circuits, including their construction, operation and gain. Shortly we will be moving onto tuned circuits, which links nicely with the post ‘Learning about Tuned Circuits’ which was published back in April last year.

PLC Transmission Mechanisms

In the PLCs unit we have been learning about the various types – unitary, modular and rack mounted – as well as different I/O devices for these and the transmission mechanisms. I found this part of the unit particularly interesting, looking at how much transmission mechanisms have changed and improved over the years, while looking at the advantages and disadvantages of twisted pairs, coaxial and fibre optic cables.

Twisted Pair

A twisted pair is the oldest out of the three transmission mechanisms and consists of pairs of copper wires twisted around each other. Twisting the wires causes EMI and crosstalk signal to cancel itself out, which is a type of destructive interference. As the wires are twisted EMI should affect both wires equally and is therefore canceled out. There are several types of twisted pairs, the main of which are UTP and STP. UTP stands for Unshielded Twisted Pair, this is the cheapest mechanism of transmission, although it is susceptible to radio and electrical frequency interference as there is no shielding. To overcome this issue we also have STP – Shielded Twisted Pair – these come in three forms to help minimise interference and extend the maximum distance of the cables, where either:

• Each pair is individually shielded with foil.
• A foil or braid shield inside the jacket covering all wires (grouped).
• A shield around each individual pair as well as around the entire group of wires (double shield twisted pair).

Twisted pairs are divided into categories according to the application requirements and are backwards compatible.

Image source: darren-criss.org

Coaxial cable

Coaxial cable is a transmission mechanism which conducts an electrical signal using an inner conductor (usually copper wire) surrounded by an insulating dielectric layer which is enclosed by a shield layer (usually a woven metallic braid). This is then protected by an outer insulating jacket. Normally the woven metallic shield layer is GND and a voltage is applied to the inner conductor to carry electrical signals.

Design choices of coaxial cable affect physical size, frequency, performance, attenuation, power handling capabilities, flexibility, strength, and cost. This type of cable is more expensive than a twisted pair by a factor of two to three, however, it is less prone to interference as it has much better shielding. Most commonly coaxial cable is used in TV applications and sometimes used for digital network transmission.

Image source: wikipedia.org

Fibre Optic cable

Fibre optic cable is a transmission mechanism containing at least one optical fibre which is used to carry light. The cable itself consists of a bundle of glass threads, each of which is capable of transmitting messages modulated onto light waves. The optical fibre consists of a core and a cladding layer which is selected for total internal reflection due to the difference in the refractive index between the two. The ends of the cable can be terminated with a specialized connector so that it may be easily connected/disconnected from transmitting and receiving equipment.

Fibre optics are not affected by power surges or electromagnetic interference. Corrosive chemicals in the air also have no effect on fibre optics, making them ideal for factory environments where electrical interference is very high. Dependant on the application, fibre optic cables can be armoured to protect them from external conditions, such as agricultural machinery and animals. The higher the risk of damage to the cable the heavier they are armoured. This type of transmission does however come at a cost, as it requires specialist skills which may not be readily available.

Image source: errantscience.com

BCS OSSG Student Competition

Following entering the BCS OSSG Open Source Project Student Competition a couple of months ago, last month I found out that I had won in the category for Best Apprenticeship Project, with The Light Theremin Project. In the middle of last month I went down to the BCS offices in London to give a presentation on my project. I was quite nervous to say the least, considering I hadn’t given a talk on anything since Wuthering bytes 2014 where I gave a lightening talk. Needless to say it was a fantastic experience and it was great to hear about what projects other people around my age were working on.

Dan Gorringe won the for the category, Best School Project, with The Next Generation of Open Source Engineers. In his presentation Dan spoke of making the ‘worlds cheapest supercomputer?’ using Pine64 boards. The full article on Dan’s project can be found at www.embecosm.com.

Luke Robert won for the category, Best First Year Project, with The use of Open Source projects to scaffold the development of new programmers. In his presentation Luke spoke of the benefits of being a student and able to learn from looking at the source code.

Further Debugging RC2014

Since Assembling RC2014 I’ve been looking at a new ways which I can go about debugging the modules. One method which I am going to attempt is connecting LEDs to each of the address and data buses. By doing this in theory the LEDs should flash when the bus lines are toggled between high and low. To do this I will use a Darlington transistor array. Hopefully this will work and it will be a good way to see what lines are being toggled high and low and also at what point. Unfortunately debugging is currently ongoing but I hope to have a fully working module soon!

This month I have also registered to attend The IET Young Women Engineer of the Year Awards 2016 at the beginning of December. I attended last year and really enjoyed it. I think its great to hear how about the career path candidates have taken and what they have acheived so far in their careers.

I had a week off from my HND for October reading week, which coincided with a week which I had off work too. I took the chance to do some things I’ve been meaning to for a while. As well as trying to get on top of assignments, I took a trip down south and met up with a friend to visit some of the sites like Salisbury Cathedral to see the Magna Carter, and Stonehenge!