Created; 12/08/2009, Changed; 19/02/2024, 19/01/2024

Robust Electronics design methods

You don't need minimal and elegant design in order to get good functionality, necessarily, but complexity may be the easiest place to start.  That is, by using lots of components to create many simple to understand circuit function blocks that in turn create a simple-to-follow system, is fine.  The block diagram would then simply coincide with each circuit function blocks, and each circuit block would do one function.  This is not always possible or desirable, but the point is to design and plan as far as you can see.  The design can be refined and functions combined or split up later when you can see further.

The circuit below is an electronic fuse and is a development of the current limit circuit at the bottom of this page.  

The first diagram is a novel circuit that produces negative resistance - the current first increases but over a small voltage range, then drops as the voltage increases further.  I developed this in 1976/1977 when I was a teenager, learning about JFET transistors.  This is an application of manufacturers' components rather than a patentable novelty. 

The function block can be used to discharge remnant power in a circuit to ensure a clean power off/on reset.  I have come across this circuit used as an over current input protector in recent years.

The second circuit is a variation of the first that makes the over current circuit breaker less likely to falsely trigger.  A delay has been added.

The addition of two Zener diodes and changing the N-ch-JFET to a high voltage depletion mode MOSFET or JFET make this circuit operate at a higher voltage than the first circuit.

These circuits were drawn using OrCAD 16.6 or 17.2 Lite. (AL-0014-01a & AL-0014-03b)


I give examples like this of circuits and block diagrams to illustrate points on robust design, techniques for noise minimisation and good electromagnetic immunity.  It is not always desirable or possible to split the circuit or any design into separate components for each function. 

The key to the very good feel and performance of the camera below, for its time, is that many of the functions are integrated together with many components that only work very well because they are combined. 

The current regulator further below was combined with a switch, two functions combined so that a low voltage switch could be used.  Ultimately, the design uses a separate switch, so the two functions are separated.

I have taken lots of pictures with this Agfa Silette I

This Agfa Silette I camera, which is not electronic, but the construction looks simple, but it is not, the lens is particularly good sharp and very tolerant of incident sunlight.  There are baffles between each of the three glass elements within the lens to absorb scattered light.  These mat black baffles make the camera cope well with most incident light on the lens.  The slightly wide angle lens is sharp over the whole picture frame and the approximate focus method works very well.  The iris and shutter are within the lens near the focus, but components at this location are not focused, so the shutter can not shade part of the film.  By comparison, a Single Lens Reflex camera's focal plane shutter can stretch or shrink objects fast moving in the same plane as the shutter.  Also by comparison, if the flash is longer duration than the shutter synchronisation speed, this does not result in a partial exposure of the film that would happen with an SLR. 

Once you become a proper camera nerd (put-down way of saying expert) and can estimate light, distance and use a meter, this is the most predictable camera I have.  That is, I look down at the camera to see all the settings are correct (which I have been adjusting as I carry the camera around).  Also having a light meter is useful at around dusk but can be a distraction and at other times estimation is usually the best all round compromise and using the guide on the film carton is fine.

The Silette 1 was purchased second hand in 1973 for £5.00 (a bit more than a junior day's pay) from a camera shop.  The camera is capable of capturing unshaken sharp pictures.  It took me a long time before I started to get good pictures, then in about 1982 I went to Norway and took 5 roles of Fuji slide film and got 99% success, then my interest in photography was captured.  The silent operation and the user is not distracted by anything else than picture composition when looking through the view finder is a particularly good feature of this camera I particularly missed when I started using an SLR that is also true of the digital camera.

Trivial example of a circuit design cycle - plain and simple verses clever and elegant design - Switched current source

Comparison with the design of electronics;

The Silette I camera above is designed with a combination of single function blocks, such as the film winder and also multiple function blocks such as the lens that has settable distance, three glass elements to focus the image over the entire area of the film in a flat plane and baffles to minimise flair due to incident that causes fogging of the picture as well as aperture and the shutter mechanism are placed were the image is not focussed.  Other functions (parts) are styled as one multiple function block, a camera, but are separate functions put together.

Constant current Source with a switch (AL-00025-01D CADSTAR 18)

These current sources' tolerance is wide, but a more accurate current regulator could be made using a 3 terminal regulator such as LM317.  

Note; Circuit 2, protection diode D1 is almost certainly not required because the MOSFET probably has protection diodes within in it and if an FET where uses Vg to Vd may withstand the higher voltage the datasheet should be checked, it is possible that the drain leakage current would be higher than the gate reverse current allowed.

Like the camera, electronics tends not have single function blocks either, at the least there is usually a circuit board, screening and filtering to consider together with the function blocks required. 

Start by drawn something roughly with pencil and paper rather than use electronic drawing tool - drawing with paper and pencil so that you are not distracted by technicalities of learning a CAD tool.  Expect to redraw your circuit, may times.  You can redraw the circuit using a CAD tool later as a learning exercise. 

In conclusion the current source and switch function are separated for clarity but the comparison in the case of the camera above is more complicated.  The benefit that the Single Lens Reflex Camera may have over cameras like Silette I or a Twin Lens Reflex (below) is that the lens is a detachable component.   Also, the image viewed, when taking close up pictures, is as the imaged to be captured on film.  But other disbenefits of the SLR design is that the lens requires mechanical or electrical coupling to the camera body in order to operate the aperture diaphragm, shutter release and to inform the camera's metering system of the aperture setting.

The Yashicamat below is a 2 1/4" square format, Twin Lens Reflex camera is not elegant, and it is hard to use.  It produces excellent professional results.  A similar point to the one I was making about the current source with a switch.  Like the Agfa above the TLR's shutter exposes the whole of the film simultaneously at all shutter speeds, this is not the case with an SLR though.


Play and exploring ideas is important in developing high quality design, whether the requirement is simple or elegant

The Yashicamat is equal to a professional Rolleiflex or Rolleicord.  Not that you need a fruit basket and a 1962 vintage radio (Vintage? I went with dad back to Strange Electrical in Sevenoaks when he took it back many times to be fixed under guarantee in the end only the VHF band worked which is what my father wanted) as well, but it is a lot more work, and you need to use a sturdy tripod to do achieve that quality and a tape measure is useful for setting the focus because the camera only has a magnifying glass as a focusing aid.

I should also say once I got used to them the Nikon SLR was good but the Cannon AE-1 SLR is an exceptionally nicely designed camera to take excellent pictures with all setting to hand.  My modern digital IXUS is excellent easy to use cameras gives better results than the AE-1 but does not have that plain simplicity of feel (use) and look of the Agfa.

The reflex mechanism (SLR & TLR cameras) is a spring-powered mechanism that is wound up when the film is wound-on and providing a wider range of shutter speed settings from; Bulb, 1 to 1/500th second.  The view find front is open (right below) so that you can view the composition by looking through rather than looking down at the screen (left).  Both types of cameras but all types are suitable for portrait photography, but the drawback is that to get the picture you need to get the attention or the subject to see the moment and take the picture otherwise the subject will become distracted, but no amount of pictures too late will capture what you want.  Both pictures are taken with camera phones using available light are technically poor, but I think the composition is good.  The first tong-in-cheek exaggeration to illustrating the amount of things you have to do and need before you can take a picture with a good film portrait camera, but I've not achieved anything worthwhile with the Yashicamat.

Very modular kit necessary to take photos include, Camera, Lens hood, Flash mount, Flash cable, Flash, Shutter release cable, Removed knurled nut to fit the shutter release cable, Tripod.  Photos of the Yashicamat were taken using Ericsson and Nokia phones. Also, useful are a light meter and a tape measure to set the distance close up and estimation for distant focus is good instead of using the magnifier above the screen.

Left.  Olympus Trip 35, solar-powered semi-automatic camera.  Single speed, electro-mechanical. The voice-coil iris mechanism is activated when the shutter release is pressed, then the shutter briefly opens.


Personal profile - summary of my approach to design;

I have been interested in electronics since my childhood, deciding that I wanted to do electricity when I was five.  I have always worked in Electronics, As a Technician then became an Electronics design engineering since 1975.

Furthermore, I am retired now.  I used to do non-military Electronics Design before I retired, sometimes from home, popping in as required.  There are a number of good quality makers and assemblers of PCB designs, so that CAD and BOM files can be sent away, questions answered, then completed boards sent and often loaded and running software successfully before I had seen them.

To discuss these electronics pages, see; Blog page Electronics 

First page; Beginners Guide