Flicking through the pages of a hobbyist electronics mag, there are stepper motor drivers for £18 and LCD drivers including display, also for 18 pounds. Both kits are based on PIC microcomputers.**
For those of us who like to "Roll our own", (isn't that all of us?) it would seem that the cost of manufacturing our own Quotient Mistress, using off-the-shelf professionally produced circuit boards, is about £36.
You can indeed buy those kits from Magenta (and I bought and assembled them myself in the early days of my experiments with stepper motors - they have long since been discarded, having served their useful but very limited purpose), and separately, each kit will allow you to drive a stepper or an LCD display (but not both together). They are great for learning how PICs work & experimenting with LCD and stepper motor driving, but that's about it, and for anyone that has the interest I would recommend them as a cheap way of finding out more about these fascinating devices.
As I am sure you are perfectly well aware, but conveniently choose to gloss over, there are some significant differences between what you would be able to do with these 2 kits and what DivisionMaster can do:
- Once you have interfaced the LCD to a PIC 16F84 (needs minimum of 5 I/O lines) and the stepper drive (the way they do it, using full phase drive, they use 4 I/O lines), you have unfortunately run out of pins on the 16F84 to drive a 16-key keyboard (needs another 8 I/O lines which you haven't got unless you move up to the bigger PICs, like the
40-pin devices in the 16F8XX series and the 18FXXX series). Of course, you could go for a twin-processor approach, which would give you a total of 26 I/O lines between the two PICs, in which case, good luck to you as you try to partition the functionality you need across the 2 PICs and devise a suitable communications protocol to connect them together (which would cost you at least 2 more I/O lines of course).
- DivisionMaster has a bipolar (not unipolar) output stage capable of driving motors at up to 2A/phase, as opposed to the 1A unipolar drive on the Magenta kit. So you would have to factor in the 2A/phase H-bridge circuitry & decoding logic, and while you're at it, the means of controlling the motor current from the PIC, which DivisionMaster can do; with the simple unipolar drive circuit used on the Magenta kit, the only way to adjust the motor current is via fixed resistors in series with the motor coils.
- The PIC 16F84 they use in the kits is a 4 MHz part (there is a 10 megs part available these days, but they don't use it in the kits to keep the cost down). Consequently, the step rates it is capable of generating will be between 1/4 and 1/8th of the step rates that can be had with the bigger PICs that can be clocked at 20 or 40 MHz. DivisionMaster can generate a pulse rate of up to 10,000 pulses/second (actually, it can do significantly better than that, but that is the maximum that can be programmed in from the keyboard).
- The 16F84 has a very small amount of program memory (only 1K), so you would run out of memory space long before you had created anything remotely like the range of functions and features that DivisionMaster supports. At the last count, my firmware takes 2K to store the character strings for driving the LCD display, and the maths libraries for LCD display, keyboard access, and 8, 16, and 32-bit fixed point arithmetic, and that is before you have written a line of application code.
- The PIC 16F84 has no non-volatile RAM, so (unlike DivisionMaster), there is no way for it to remember any operating parameters from one day to the next. So you will have to factor in a bit of external flash RAM in your design to cope with that, unless you want to enter the operating parameters every time you use the machine, on that keyboard you can't drive because you haven't enough I/O lines. And of course, there's no space on the Magenta boards for adding NV RAM chips or their supporting components.
- The kits from Magenta don't include a power supply, let alone one capable of generating the necessary 1A/phase to drive the motor - you have to source that yourself. Or you could of course use Magenta's bench PSU kit - variable output up to 25V at 2.5A, which is just the job - as the Magenta stepper kit is a simple unipolar drive, the PSU will need to be able to source 2A continuous at whatever voltage you choose to use, as the step sequence involves 2 motor coils being energized at the same time. I have bought & built one of their bench PSUs, and it works extremely well. Kit price for the bench PSU is a very reasonable £65 by the way.
- You have also conveniently neglected to mention the cost of the keyboard hardware, a suitable case, mounting hardware, plugs & sockets, interconnecting cables, keyboard membrane...etc., none of which are provided in the Magenta kits.
- To make any sense out of these kits over and above the trivial sample programs they contain, you would need to provide yourself with the software and hardware tools to program them to do anything other than the rather trivial pre-programmed functions that they perform "out of the box". Magenta sell a variety of programmer kits - you're looking at a minimum of £26 (again, don't forget the cost of the power supply, which is an extra £4 with these kits) for a parallel port connected programmer. However, make sure you don't make the mistake of trying to use any of these tools that are designed for connection to a parallel port of a PC if you are using NT or any of its derivatives (WIN 2K, XP etc), because you will find that they don't work, as NT doesn't allow applications direct access to the I/O ports. Magenta's "Icebreaker" system (which uses a PC serial port & works on NT) is great for breadboarding PIC projects by the way - £39 with power supply, but it only works with their own specially programmed 16F877's and the upper 4K of memory can't be accessed, so it wouldn't help you with the '84's. FED
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will sell you a nice serial port connected PIC programmer for about £45 plus the cost of a PSU, or one fully built for USB connection (no extra PSU needed) for £95. They also do very nice software development tools, but you're talking another £50+ on top of their programmer prices.
- And when you're done cobbling these 2 kits together, don't forget the EMC testing you need to do for CE compliance. And no, the fact that you build it yourself & it is not for resale doesn't exempt you from the legal obligation to comply with the CE regs, as I am sure you understand from your ham radio experience. So if your home-built stepper driving device causes interference that screws up your neighbour's sensitive electrical equipment, you are liable. The most reasonable testing house I have found to date charges around £800/day to use their labs and services; figure on a minimum of 2 days, if you are lucky enough that it passes first time without the need for re-work.
So, all in all, I'm not remotely worried that you are likely to give me any competition with your kit-based "solution" anytime soon. Or anytime before Hell freezes over, for that matter. QE definitely not D, Old Man.
However, yet again, I must thank you for the additional publicity you are giving my company's products, and on behalf of Magenta's owner (who is a friend of mine, by the way), thank you very much for advertising their products too.
So you choose another in the range, or conceive of functional partition between two of them? All fairly trivial stuff. If you think otherwise, perhaps that is indicative of inexperience on your part which may contribute to your excessive costs?
A red herring. 1000 pulses per second is more than sufficient for a hobbyist's workshop. The "Measure twice, cut once" mantra will mean that extra speed (and the excessive costs associated with it) will go to waste.
With a 200 steps/rev motor and a 60:1 worm, that's 12000 steps per rev for the workpiece and a matter of only 12 seconds to go right around. Neither here not there.
If you're buying in maths libraries then perhaps that shows up an excessive costing and also your inexperience? 32 bit integer arithmetic is all that is needed, no trig or exponentials. Set your minimum "integer" value to be 0.001 (or even a tenth of that) and Bob's your uncle! 8 and 16 bit arithmetic is well handled by 32 bit routines.
I looked at your glossies - the "functions and features" that you supply are trivial extensions of each other and ably handled by a well-factored set of routines..
Sure, there are memory limitations in some microcomputers, choose whichever in the range is appropriate once you've produced your design. All very trivial, again.
Sales blurb. Irrelevant. Rarely is the hobbyist doing mass production using rotary tables. Even if so, the number of parameters to be set up is so small as to be a non-problem.
You're not right there. the holding current is less than the stepping current for any stepper. Power supplies? Old car battery plus float charger - to hand for most of us.
£26? Wow! So you have to buy some support tools for everything that you make -sounds par for the course for any hobbyist activity; but like other hobbyist activities, you've then got the tool on board for further projects.
In a commercial environment, £26 amortised over several sales (especially the "dozens" that you claimed at Donnington) is only s few pence per unit; nothing to justify an end price of £280.
These days you self-certify to CE using your own test logs. If you're paying £800 per day, then more fool you; but there's no reason your clients need pay for your folly.
I have never suggested that I'm giving you any competition.
I am encouraging others to have a go themselves, for that is the spirit of the hobbyist and his workshop. However, in response to a suggestion that your goods were overpriced, you yourself suggested that you were a cynical trader.
I see your point, but in the case of overpriced goods it is not the case that "any publicity is good publicity"; witness the BBC's Watchdog program.
As to Magenta's I have no regret in publicising what appear to be extremely good value-for-money goods, in sharp contrast to the overpriced (and over-engineered as you now reveal) product that you have admitted to be cynically trading.
1 Amp will not move a 6" rotary table with plain bearings against frictional forces. Tables with thrust races in them are well beyond simple hobby import prices.
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