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Old 1st Jan 2016, 8:29 pm   #1
high_vacuum_house
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Smile Maplin Minilab completed !!

good evening,
Over the Christmas holiday period I finally had time to make up and complete the Maplin Minilab project I was asking construction and circuit details of.

It is a stabilised multi-voltage power supply built around 78XX and 79XX voltage regulators with 8 TTL inputs and outputs, a 1Hz/1KHz clock and a debounced switch. and ideal for testing and development of op-amp and digital logic circuits. This one I hope to teach my 2 sons when they start to grow up analogue and digital electronics.

With a circuit diagram I bought all of the components needed to complete the project and I waited until I had every component before commencing with the project. I think I spent around £55 on components including £20 each for the transformer and case.

I was extremely impressed with the quality of the case when it arrived. It is very well made and ideal for the task.

It was a shame the 4mm test sockets I bought were of extremely dire quality and even the backnuts were not even round!! Some didn't even have a thread! I was surprised that anyone could have had the guts to sell them as sockets!! Belling-Lee or Mr. Bulgin would be spinning in their grave if they came out of one of their factories!!. You certainly have pot luck buying electronic components these days!! I managed to get some better ones and used these instead.

The construction was fairly straightforward with no peculiar issues coming to light. The board construction took a few hours and the mechanical construction/wiring and testing took 2 days to complete.

Other than the wiring of the mains switch was back to front which meant the neon was on all of the time, and the variable output pot worked in the wrong direction, the Minilab worked properly first time.

I am very impressed with the outcome of the project and it should last a long time.

Christopher Capener
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Old 1st Jan 2016, 9:19 pm   #2
David G4EBT
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Default Re: Maplin Minilab completed !!

Pleased to learn that you've completed the project and that it works Christopher. I've dropped a note to the member of the EPE 'Chatzone' who came up with the 'unobtanium' PCB, to let him know that it did get put to good use, having languished in his drawer for a couple of decades or more!
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Old 2nd Jan 2016, 11:00 am   #3
mhennessy
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Default Re: Maplin Minilab completed !!

Very good - nice and tidy

I used that exact case to build a bench PSU nearly 20 years back, and was also quite impressed with it. And not too expensive either. From what you say, it seems that they still available today - where did you buy yours from?

All the best,

Mark
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Old 2nd Jan 2016, 11:48 am   #4
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Default Re: Maplin Minilab completed !!

Looks like a nice little project.

Those cases are really rather good: I've got a larger one here, containing a "roller-coaster" coil and 500pF wide-spaced variable capacitor for my 160/80/60/40M antenna tuner.
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Old 2nd Jan 2016, 1:25 pm   #5
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Default Re: Maplin Minilab completed !!

Quote:
Other than the wiring of the mains switch was back to front which meant the neon was on all of the time, and the variable output pot worked in the wrong direction
This happens too often for sheer (un) luck!
 
Old 2nd Jan 2016, 1:45 pm   #6
mhennessy
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Default Re: Maplin Minilab completed !!

But much more annoying if you've soldered the connections
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Old 3rd Jan 2016, 11:57 am   #7
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Default Re: Maplin Minilab completed !!

Quote:
Originally Posted by mhennessy View Post
... where did you buy yours from?
You can get those cases from http://makerbase.co.uk/

I bought one to house a computer PSU to bench supply conversion.
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Old 3rd Jan 2016, 12:08 pm   #8
mhennessy
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Default Re: Maplin Minilab completed !!

Thank you! Prices seem pretty reasonable too...

Mark
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Old 3rd Jan 2016, 12:29 pm   #9
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Default Re: Maplin Minilab completed !!

They also trade on the bay as earthgazer if you collect Nectar points or other deals to make your purchase cheaper.
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Old 3rd Jan 2016, 12:33 pm   #10
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Default Re: Maplin Minilab completed !!

Quote:
But much more annoying if you've soldered the connections
I disagree, a soldered joint is quite easily moved, quicker than a terminal block.
 
Old 3rd Jan 2016, 1:43 pm   #11
mhennessy
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Default Re: Maplin Minilab completed !!

Not if you've done it properly (e.g. fed tinned wire through hole in terminal, wrapped around several times and "squeezed up" to get a good mechanical joint, applied heatshrink sleeving or equivalent to the completed joint, applied tie-wrap or similar mechanical support to the bundle of cables within an inch of the terminals, applied insulating boot over the whole assembly, applied tie-wrap to that to stop it coming away). In practice, it's easier to just give up and start again.

I suppose if you just "tack-solder" to the side of the terminals, then you might be right. But as we're talking about mains connections here, let's assume that we're not doing that...

Besides, Christopher used push-on crimp connectors. Quite right, too
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Old 4th Jan 2016, 10:47 am   #12
richrussell
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Default Re: Maplin Minilab completed !!

I'm going to have to get the one I built from the kit back in the late 1980s out and sort out the failed LM78xx components now. Mine's in the original plastic case that Maplin sold specifically for it.
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Old 7th Jan 2016, 5:59 pm   #13
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Default Re: Maplin Minilab completed !!

This thread reminded me that I too had built one of these from a Maplin kit. I haven't used it for years but I've dragged it out of the cupboard. It is certainly a solidly designed bit of kit and mine has a steel case with dark grey hammered finish cover. The components supplied were all of good quality even if the red plastic terminals have faded somewhat with age.

Now to check it out and perhaps give it a new lease of life.

Edward
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Old 17th Feb 2016, 9:36 am   #14
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Default Re: Maplin Minilab completed !!

Here's mine - actually apart from the -5V regulator only putting out -2.5V, and the variable output voltage dropping when under any sort of load, it's all still working fine. The circuit is on the original veroboard soldered by a 15 year old me, back in 1989.
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