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Old 15th Jan 2019, 5:47 am   #1
ajgriff
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Default The Marmite VR - AD584 Voltage Reference

This bit of fun began when I ordered one of those really cheap AD584 modules from China a few weeks before Christmas. The slow boat finally arrived in port and the module dropped on the mat on Dec 28th which gave me the opportunity to excuse myself from the ongoing festivities in order to visit the workshop for an hour or two.

Iíve always rather liked the shape of Marmite jars, the design of which hasnít changed much since the start of production in 1902, and had consigned one to the recycling box the previous evening. Why not house the module in the jar I thought? With the jar retrieved I set about creating the item you see in the attached images, all very basic but entirely functional. It is interesting that, like the jar, the AD584 is a vintage design although it only dates back to the 1980s.

For many years Iíve enjoyed messing around with photo-editing & graphic design software so that evening, whilst the rest of the family apparently enjoyed a really dull film (Darkest Hour?), I was able to sit unobtrusively with my tablet and create the labels for The Marmite VR. Again, fairly basic but films are of limited duration.

The accuracy claimed on the label is simply an assertion based on the readings of a Fluke 25 calibrated by the MoD in 2014 and Mark Hennessyís informative review of these modules published on his website. In any event The Marmite VR provides a quick way of partially verifying the accuracy of my small selection of Flukes, AVOs and oscilloscopes to a degree that is more than adequate for my purposes.

Most home brew projects, whatever their scale, throw up at least one unexpected challenge. In this instance it proved to be the empty jarís lack of weight as the assembly tended to slide around the work surface when in use. The solution was to half fill the jar with ballast in the form of Fullerís earth cat litter sealed with diluted PVA glue.

Love it or hate it I hope The Marmite VR brings a smile to one or two faces in the depths of Winter. After all a hobby should be fun shouldnít it? Inexpensive fun too, as the total cost was no more than the retail price of a fresh jar of Marmite. Incidentally, for the benefit of anyone associated with Unilever, Iím not intending to mass produce these units so there is no need for litigation over branding.

Alan
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Old 15th Jan 2019, 7:28 am   #2
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Default Re: The Marmite VR - AD584 Voltage Reference

Brilliant! Nice work and attention to detail.

Andy.
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Old 15th Jan 2019, 8:58 am   #3
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Default Re: The Marmite VR - AD584 Voltage Reference

Neat, pedantic mode, shouldn't it be "Maximum error 0.1%"?
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Old 15th Jan 2019, 12:19 pm   #4
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Default Re: The Marmite VR - AD584 Voltage Reference

Fab-u-tastic!
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Old 15th Jan 2019, 1:18 pm   #5
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Default Re: The Marmite VR - AD584 Voltage Reference

You've steampunked a Marmite jar! Is nothing sacred?
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Old 15th Jan 2019, 1:19 pm   #6
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Default Re: The Marmite VR - AD584 Voltage Reference

Quote:
Originally Posted by merlinmaxwell View Post
.... pedantic mode, shouldn't it be "Maximum error 0.1%"?
You are quite right of course as the statement currently says exactly the opposite! Can't believe I didn't realise but will correct the label accordingly.

Alan
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Old 15th Jan 2019, 1:24 pm   #7
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Default Re: The Marmite VR - AD584 Voltage Reference

Quote:
Originally Posted by Kentode View Post
You've steampunked a Marmite jar! Is nothing sacred?
At least it doesn't have a light fitting sticking out of the top!

Alan

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Old 15th Jan 2019, 1:44 pm   #8
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Default Re: The Marmite VR - AD584 Voltage Reference

Quote:
Originally Posted by ajgriff View Post
Quote:
Originally Posted by merlinmaxwell View Post
.... pedantic mode, shouldn't it be "Maximum error 0.1%"?
You are quite right of course as the statement currently says exactly the opposite! Can't believe I didn't realise but will correct the label accordingly.

Alan
Or, stick with original words but change the figure from 0.1% to 99.9%.
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Old 15th Jan 2019, 6:31 pm   #9
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Default Re: The Marmite VR - AD584 Voltage Reference

Corrected label before printing.

Alan
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Old 15th Jan 2019, 6:54 pm   #10
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Default Re: The Marmite VR - AD584 Voltage Reference

Ah, that's better, my mind is at rest (grin).

In a production environment it would be "Label (exterior) 7439 Rev 2 Issue 1 ECN* 4327" (even more of a grin).

*Engineering Change Note
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Old 15th Jan 2019, 7:00 pm   #11
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Default Re: The Marmite VR - AD584 Voltage Reference

Even Fluke get it wrong (from a 115 datasheet) I would have thought that 98% accurate would have sounded better to the marketing department.
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Old 16th Jan 2019, 2:34 pm   #12
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Default Re: The Marmite VR - AD584 Voltage Reference

Since I too have occasional tendencies towards the pedantic end of the spectrum I've checked the accuracy statements of a number of test equipment manufacturers including Fluke, AVO, Tektronix and Hameg. Interestingly they all quote accuracy in terms of the error percentage for example, the Tek 465B manual states that the accuracy of the vertical amplifiers is 'within 3%'. I'm inclined to think, therefore, that the original Marmite VR label is in line with industry practice.

Alan
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Old 16th Jan 2019, 6:11 pm   #13
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Default Re: The Marmite VR - AD584 Voltage Reference

I've shown your creation to my daughter Alan! She not keen on electronics but has a great interest in both Marmite and Design. I think it's brilliant-especially the cat litter "ballast". You hoped people would be amused whether they love it or hate it. I think most people will be positive but ironically, if it does generate opposing views then it will [literally] be a "marmite" object-like the brown yeasty stuff itself

Dave
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Old 16th Jan 2019, 6:35 pm   #14
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Default Re: The Marmite VR - AD584 Voltage Reference

The recommended supply voltage for AD584 is a bit awkward, what's a good way of getting it from dry batteries, Two PP3's and a diode? At yeast that would make it portable.

Dave
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Old 16th Jan 2019, 9:54 pm   #15
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Default Re: The Marmite VR - AD584 Voltage Reference

Maximum supply voltage of the AD584 is quoted as 40v and it works fine with no output variation at 18v so two PP3s would do the job without the need for a diode.

I use the stabilised bench supply for things like this when continuous regular use is not a requirement.

Alan
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Old 16th Jan 2019, 10:29 pm   #16
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Default Re: The Marmite VR - AD584 Voltage Reference

Thanks Alan, i had hoped 18v was close enough, just need to find a project box at some point. (and a better system of swapping between 2.5/5/7/5/10 than those fiddly little shunts)

Dave
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Old 16th Jan 2019, 10:54 pm   #17
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Default Re: The Marmite VR - AD584 Voltage Reference

Two pole four way wafer switch would be the ideal solution Dave. Too much complexity for my simple little project. Even the on/off switch is a bit of a luxury but I happened to have a miniature one in the spares box.

Alan
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Old 17th Jan 2019, 11:43 am   #18
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Default Re: The Marmite VR - AD584 Voltage Reference

Jolly good fun this, as a hobby should be.

I once made a theremin using LDR's, some 555 timers, 1/4" jack & a PP3, all housed in a Colmans mustard-powder tin.

At the right angle, the lid of my Theremin looks like a smiley face too. If there's interest, I'll dig it out & take a snap of the device.

Mark
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Old 17th Jan 2019, 3:14 pm   #19
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Default Re: The Marmite VR - AD584 Voltage Reference

Quote:
Colmans mustard-powder tin.
Brilliant for RF stuff until the plastic lid was introduced.
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Old 20th Jan 2019, 1:00 pm   #20
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Default Re: The Marmite VR - AD584 Voltage Reference

I'd love to see photos of the mustard tin Theremin if it can be found Mark.

Alan
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