Ronan,

This post was perfect timing for me! I am putting a PLC system together that runs a couple of inverter drives and other stuff including HMI screen controls with modbus serial network linking it all up!

I also need to do some FFT on the input sensors to get a particular set of frequency magnitudes out for control loop return and the PLC ladder logic just can't cut it….. so I am using an Arduino to do signal processing in real time and dump the conditioned response on the stupid PLC – and you think an Arduino is a cut down PLC, that makes me chuckle! The Arduino is much more capable and is close to the PIC microcontrollers that I am used to as far as I can see but with less development work needed as the hardware probably already exists

Mark

Michael,

You might have been better off with the genuine article, I got the Arduino mega 256 development board and a couple of motor drive boards – £30 ish for the Arduine and £15 ish for the motor boards and they have two drivers on each I think. Also, as they are all Arduino make (if such a thing exists) they all plug together in a stack – they appear to be called "shields" probably due to them shielding the main board?

Mark

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Mark,

You may be right [I don't know enough to know] … but I want to drive the five-phase motor in its vintage mode, which involves five bi-polar connections instead of the new-fangled Pentagon wiring.

£8 has bought me five Boards, each with two Full H-Bridges, [so I have 100% spare, in case the magic smoke appears]; which I shall probably arrange in a nice Pentagonal pattern, with some LED indicators; so that I can easily monitor what's going on.

So far as I am aware, none of the standard sheilds would offer any real improvement in convenience, and I would need a minimum of three [=£45 at your pricing] to drive five phases.

MichaelG.

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Note: If driving in Pentagon-wired Mode, you need half-H, not Full-H … which narrows the choice of chip, I believe.

Edit: Here is the "official" Motor Shield

Edited By Michael Gilligan on 24/10/2014 23:28:53

Edited By Michael Gilligan on 24/10/2014 23:29:42

Ronan – Yes. I've been programming Arduinos for a while – one bit was designed for a conference in Italy in early 2007, and some other designs have been used by others in the intervening years.

Purchase one – they are cheap – it's the best way of figuring them out.

Most of the "RepRap" and equivalent printers use the Amtel processors, but without the Arduino overhead, so, yes, you can drive steppers.

One of my favourite uses is in creating model railway controllers (Lenz DCC compatible) for small, easy to use controllers.

It's all fun stuff – and learning is always a good thing.

Ronan,

You mean me?

Sorry, it's been a long day and I have spent most of it talking acronym. Anyway:

HMI = Human Machine Interface (used to be MMI or Man Machine Interface before political stupidity took over) or the little touch screen you might find working machines.

PLC = programmable Logic Controller or industrial computer running the machine.

FFT = Fast Fourier Transform which is a way of getting the magnitude of individual (or small groups) frequency in a complex analogue signal (more or less but you need to dig a little if you have never come across them).

PIC is part of the name given to Microchips RISC integrated circuits, try searching for PIC 16F84 and you should find one of their offerings.

Mark

PS, I would have edited the original post but don't seem to have that ability anymore?

Edited By Mark C on 25/10/2014 01:15:54

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Ronan,

That was my initial experience, too … which is why I was so pleased to find, and share, the document from RS Components … Have you read it? and have you followed the hyperlinks?

• One of the most convenient reference documents I have found so far, is this from RS Components. … It contains many useful hyperlinks to material on the main Arduino site.

​Now: On a practical level; I suspect that [for your shooting target] you might need a bigger motor than the typical small two-phase bi-polar that the L298 chip can drive … but you should be able to build a scaled-down "proof of concept" using readily available components. Let's call that one "Model Engineering", and thus avoid the wrath of those who might not approve of this topic

MichaelG.

Hi Ronan,
If you are familiar with programming PLCs I think I remember seeing a design that created a PLC using a PIC or Atmel micro. You may be able to find the design using Google. A wireless link should be possible using various wireless modules that are on the market. Some types would just in effect provide extended wires to the push buttons. There are other types that would provide a serial link. (As used to connect VDUs to computers years ago.) Although Bluetooth can provide this type of serial link it would not have the range. I would rule out using WiFi communications because of the complexity. To rotate a target by 90 Deg. each time could be done using just a geared motor with a disk mounted on its shaft. the disk would have four notches cut in its edge. A micro switch would be positioned so it rubbed on the edge of the disk. When the notch came round to the micro switch the switch would open. This switch would be in series with the motor so the motor would stop when the switch opened. To cause the motor to rotate by 90 Deg. all you need to do is to short out the micro switch for a short time (Just enough for the notch to pas by the micro switch.)

Les.

I don't want to put anyone off learning about modern electronics, but I have found I have had to learn a a new language. And I am finding it hard going, hopefully it will be easier for the younger people! Probably most of it is already known.

Just to get one apparently daft piece of nomenclture out of the way:

"Shield" appears to be the jargon generic term for any add-on circuit that is configured to be electrically and mechanically compatible with [at least some of] the Arduino boards.

MichaelG.

I am afraid that the definition of the Fast Fourier Transform (FFT) given above is not strictly correct. The FFT is simply an algorithm for calculating the Discrete Fourier Transform with far fewer multiply-accumulates (MACs) than the direct approach.

To start at the beginning, the Fourier Transform is an integral transform that transforms from the time domain to the frequency domain, and vice versa. The transform is inherently complex (in that it uses complex numbers) even if the time domain signal consists only of real numbers. To describe a given sinusoid in the frequency domain one needs to specify amplitude and phase; which inherently leads to a complex number. Many modern systems, like your mobile 'phone, use complex time signals as well.

The Discrete Fourier Transform is simply a sampled version of the Fourier integral, where the integral is replaced by a summation sign. The output is a series of discrete frequencies, but complex as before. The DFT can also be represented as a matrix multiplication. For a input sequence of N points the DFT requires on the order of N² operations. Each operation is complex, so it requires four real multiplications and two real additions. This can get out of hand pretty quickly! Let's say we want to do a FFT of 1024 samples every 1ms for real time control. That's not particularly fast, but it will involve 1024*1024 = 1048576 operations in 1ms. That's one operation roughly every 1ns, and remember each operation is four multiplies and two additions. You ain't going to be doing that on a PIC, not even one of their mini-DSPs!

The original Fast Fourier Transform was described by Cooley and Tukey in 1965. In essence it takes the matrix form of the DFT and splits the matrix into a series of matrices, each one of which is calculated in turn. At first sight this doesn't seem to be a sensible thing to do. But it turns out that the coefficients in each of the matrices are far simpler than those in the original DFT matrix. In fact the first matrix in the FFT only involves 0, 1 and -1. The upshot is that the FFT can be used to calculate the DFT using on the order of N*log2(N) operations. So for our 1024 point DFT that is 1024 times the log base 2 of 1024, which is 2 to the power 10, so 1024 x 10 = 10240. Quite a reduction in MACs! One issue with the basic FFT is that the results come out in bit reversed order. Some DSP chips have special instructions for re-ordering bit reversed data.

There endth the lesson, as I need to get my rear in gear and tackle the jungle that is masquerading as my garden.

If anybody is interested in the mathematics I can write some of it down and post it in an album. It is not really amenable to trying to write it within a post.

Regards,

Andrew

Note: DSP = Digital Signal Processor – a processor optimised to calculation MACs and used for high end real time signal processing

There are not many of us left

JES