The Electronic Prototype System (EPS)
See also ...
[↑ TSU Advisor index]
What is the Electronic Prototype System?
EPS is a method for the construction of small to medium sized prototype
electronic assemblies. You use it to 'package' circuit boards together
with those components which are normally accessed externally on a front
[↑Top of page]
What are the advantages of using the EPS?
Most importantly, during prototype development, testing, debugging
and adjustment, access to both the 'component' and 'solder' sides of
your circuit board is almost unhindered. This is not so for a board
sitting at the bottom of a plastic or metal box.
- It is smaller, simpler and less expensive than a 'full-blown'
racking system based on plug-in modules.
The horizontal board mounting means that you do not need extender
cards to make live measurements as you do with a card rack.
Like a module based system, it eases future alterations to any part
of your project. You add mini-panels or change them as your project
design proceeds. You can start with one or two mini-panels that you
know you will need at the beginning and later add more as time
permits, operational experience or design change requires. Make a
start with your project now, in confidence that you aren't
doing anything that cannot later be undone.
Because the panel components are mechanically fixed, the connections
to them are not at risk of flexure and breakage as they are with
open construction. Those problems arise on the morning of your
project assesment and you diagnose them only after it has been
The aluminium mini-panels and the connecting rails provide a high
conductivity signal path to earth. Inadequate earthing is a common
cause of instability, signal cross-talk and other
If your project involves mains power, or other hazardous voltages,
then open construction isn't an option. You'll need an enclosure of
The panels shield your circuit from external noise pickup better
than will a plastic box or the open construction
technique. They may also protect against damage through ESD.
It permits shorter lead lengths to be used compared with the
open construction technique and, being fixed properly, minimizes
changes to circuit performance caused by flapping leads.
Components fixed to a panel are easier to solder to than ones that
skate about the bench when you go near them with a soldering iron.
Because you are spared having to put everything on one front panel
you never have to drill extra holes in a panel that already has
components mounted on it. Marking out such holes is tricky and
metal swarf just gets in the components: aaargh!
The transportability of an EPS based project is better than the
open construction technique. Everything is tied together neatly
so components aren't damaged and wires are less likely to break off.
A small library now exists of panel designs to hold the most frequently
used components: switches, LEDs and BNC sockets etc.. The range of
'supported' components is increasing all the time. You don't have
to worry about the fine details of the hole positions or dimensions.
The library drawings are to a standard acceptable to the FEPS
Mechanical Services Unit (MSU). With your project supervisor's
permission you can quote the drawing reference number to the MSU
who will produce the panel for you.
If you wish to machine the panel yourself then you can ask for
a 'blank' already cut to the correct dimensions.
A jig has been produced which enables the panel rail mounting holes
to be drilled precisely.
If you make a printout of the drawing then you can tape it over the
panel blank and then centre punch the hole positions through the paper
- no marking out mistakes then!
The mini-panels are easier to clamp safely in a drill vice or bench
vice than a larger folded aluminium or diecast box - particularly
one which already has components on it.
You can cut, file, drill or tap the specified high strength
aluminium alloy with fewer burrs and less clogging than the softer
aluminium found in folded boxes. Its machining properties are much
more like diecast than pure aluminium.
If you make a mistake when drilling a mini panel then you only need
do the mini-panel again - not an entire front panel and all its
holes. This is quicker and far less expensive than replacing an
entire diecast box, for example.
Some components you must fix with nuts behind the panel. If you
mount those components on the side of a small box then you have no
room to access the nuts with a nut spinner. With the EPS it's no
problem to mount the components before fixing the mini panel onto
In future years, it is expected that a stock can be built up of
'recycled' panels from previous projects - you won't then have to
do any machining at all!
Panels with a standard set of connections to the board are being
given library symbols in the Eagle PCB editor. You then can treat a
panel as though it were just another 'component' in your layout.
Once done, this saves much time, trouble and wiring error.
The most expensive components in a project tend to be those mounted
on the front panel: switches, connectors and displays. If your EPS
panel is available 'off the shelf' then this could mean big savings
in cost and labour.
Recycling the panels generates less eco-unfriendly 'Waste
Electrical and Electronic Equipment'.
[↑Top of page]
What are the disadvantages?
It's more complicated and (at present) expensive than the open
The mounting rails do inhibit access to board solder sides. This
can be particularly so when using a wiring pen. You can,
however, temporarily unscrew a rail should it prove a problem.
There is still no need to remove the board itself.
You are effectively limited to a total panel width of 24 cm, and
a panel height of 76 mm. This is inadequate for just a few
It may be be less space efficient than a rack system with
In the early stages it's slower than open
At present, most components you need are not available 'off the
shelf'. You may then have to wait for a mini-panel to be
designed and made (or do it yourself).
Panels can only be machined for you following a significant lead
Components become grouped by type, rather than function. For
example, all your coaxial sockets are together on one
mini-panel, rather than input sockets on the left and output
ones on the right. This leads to poor ergonomics and, possibly,
[↑Top of page]
Can an EPS project be enclosed in a box?
The height of the mini-panels, 76.2mm, is designed to fit in the ABS plastic
box from Maplin Electronics order code BZ77J
at £10.49 each. Maplin is the only known supplier of this box; and
it may not be available indefinitely.
[↑Top of page]
Last modified: 2014 March 14th.