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Old 21st Jul 2017, 3:49 am   #21
jay_oldstuff
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Default Re: Build your own? A discussion.

Not built much of my own test gear but I did build a custom cable tester for my previous employer, before that we had a drawer full of various audio video and data cable testers and you could garuntee someone had not put back the one you needed. So I built this one big tester that covered 95% of the cables we used inclooding the big socapex multiway cables that we didn't have a tester for and used to have to test pin by pin which took ages. I fitted it all in an old control pannel I raked out of a skip. And mounted it on the warehouse wall. When I last visited about two years after I left it was still in use in the warehouse.

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Old 21st Jul 2017, 8:13 am   #22
Karen O
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Default Re: Build your own? A discussion.

Needless to say, there are no commercially available instruments for Narrow Bandwidth Television!

We have a long history of making our own caption generators, alignment tools and of course monitors.
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Old 21st Jul 2017, 8:45 am   #23
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Default Re: Build your own? A discussion.

Quote:
Originally Posted by Biggles View Post
I have built several gadgets to simplify testing in various jobs over the years. I always have the proper test gear, but who wants to hump that about when you can just plug in a little test box which fits in your pocket. For example I needed a quick test for our external phones and built a DTMF decoder, audio checker etc in a little box to quickly check them out. In a previous job, there was a need to quickly check control room operator's headsets to see whether the problem lay in the actual set, the socket, or distribution equipment. When I got calls for transmission/reception problems, quick plug in plantronics headset, wiggle the wires while listening for crackles etc and away you go, diagnosis in seconds. The trouble was, when you were spotted checking one, all the operators used to shout check mine! But it saved loads of time. So yes, it is necessary sometimes to build your own test gear.
Alan.
Same here. I am quite well-equipped with all manner of test gear (mainly RF and audio), but some times I need a quick, convenient piece of clobber that I can take into the garden to help me set up an aerial. So a cheap 'rally special' DDS signal gen board was hooked up to a home-made SWR bridge, meter and battery and all stuck in a tupperware box. Hey presto, I can quickly find out where the dip is and adjust the settings without running up and down the stairs and without buying one of those pocket VNA type thingies. It's very enjoyable knocking up stuff like this.
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Old 21st Jul 2017, 11:23 am   #24
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Default Re: Build your own? A discussion.

Quote:
Originally Posted by Skywave View Post
Related to that sub-topic, there arises the subject of 'prototyping'. I'm reading a book called "Think Like an Engineer" by Guru Madhaven.* The book has a chapter entitled 'Prototyping' in which he makes reference to the 'prototyping trap'. What he is referring to is that after the initial design work is done and a prototype is built, but then when things don't 'work out' as expected, there can be a strong tendency to modify the original design at the prototype stage to get it to 'behave' and to 'keep going'. The danger the author refers to is that by so persisting with the design at the prototype stage, one can easily miss the possible essential point that the basic concept of the design was flawed in the first place and that going right back to square one and starting again is the sensible option, but once the prototype stage is reached, psychologically, that can be a difficult thing to do.
I do get these prototype problems and over the years have learned to spot fairly well the point at which a project needs a complete makeover (or even abandoning). A parallel hobby I have is art, an I find with a painting there comes the point when you have to decide when the painting is finished and cannot be improved (maybe will be worsened) by further work. It is one of the hardest things to grasp. My workroom is littered with projects which, even if they work, don't light up the world, and also gutted cases which may be useful sometime. I mostly tend to buy new components (or NOS) and expect to have some 'wastage'. As I design most things (although usually use subcircuits from elsewhere with changes for my own purpose), I do get a number of failures but like in most things - experience counts!

Thanks for the book mention. I will take a look
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Old 21st Jul 2017, 11:50 am   #25
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Default Re: Build your own? A discussion.

With homebrew test equipment you are in charge of the build quality and will have intimate knowledge of its construction in the event of maintenance.

Equally you can design/build according to specific needs that may not be covered (or is expensively covered) by commercial devices.

...but for me it's just the 'fun' and sense of achievement DIYing gives.
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Old 21st Jul 2017, 5:03 pm   #26
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Default Re: Build your own? A discussion.

I think at the end of the day, there doesn't have to be a plausible reason for doing anything. If it makes you happy in whatever form, do it. A lot of fun can still be had just messing about with classic little simple circuits, which may well be "useless" and "out of date", but who cares, it's what we do.
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Old 21st Jul 2017, 5:45 pm   #27
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Default Re: Build your own? A discussion.

Sage words Biggles, I like buying kit (cheap stuff for the fun of it too) and making stuff. All great fun. I look at my hobby as a fun skills enhancing exercise, very useful when in a job and an unexpected thing crops up. It is great to be able to make things and understand how bought stuff works too.
 
Old 21st Jul 2017, 7:59 pm   #28
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Default Re: Build your own? A discussion.

Some wise person once pointed out that you do the 'day job' to make money. Some of which you spend on essentials (food, housing, power, etc). And some/all of the rest on you hobbies. Almost by definition, hobbies lose money. So don't try to justify them financially.

My view is that the important things about a hobby are that you enjoy it and that it doesn't harm people unconnected with the hobby. Making test gear clearly satisfies the latter, so if you enjoy doing it, do it!

As I said earlier it is probably better to buy a multimeter, if only because it will be sort-of calibrated (how 'sort of' depends on the manufacturer!). You can of course then make other multimeters, think of ways to calibrate them accurately if you feel so inclined. And like many others here, I find making electronic devices (test gear and others) to be enjoyable. So I will buy some instruments new. Buy some second-hand and restore them. Build some from components. I don't _have_ to, I just enjoy it.
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Old 21st Jul 2017, 9:16 pm   #29
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Default Re: Build your own? A discussion.

There's a mid point which I find quite satisfying actually which is buying broken test gear and making it not broken again. My hall cupboard has about 30 items in it. I need to update my will.
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Old 22nd Jul 2017, 12:17 am   #30
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Default Re: Build your own? A discussion.

There are times of course when commercial kit is not available.
I design and build transformers, and I could not find any equipment for testing them. Yes plenty of inductance bridges available but no DC to upset the BH curve in swinging and smoothing chokes. An output transformer needs be tested for frequency response at rated power and leakage needs testing.
Different current in each half of a push pull traffo. etc etc
So I made one!! Its quite a simple tool using some large power resistors, a variac driving a transfomer to apply DC, and my audio oscillator plugged in to do frequency tests. A second transformer for applying AC, again with the Variac to control the volts applied to the unit under test.

On a totally different level I have been building stuff since I made my first electric wireless in the late fifties under dads instructions. It is a real pleasure to design and build bits n pieces. In fact its my therapy . If I dont build "something" every couple of months, I start dreaming design .

In regards to engineers in general I am quite a poor one , having worked beside some real masters. Modern engineers Most of them are board jocky's, they do everything with a computer and cannot handle even the simplest math!! As far as component level work goes, most of them cannot even solder properly, drill a hole without breaking the drill, or bend up a simple chassis.

I actually call the "paper engineers".

Just my take on the subject.
with regards to all
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Old 22nd Jul 2017, 11:09 am   #31
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Thumbs up Re: Build your own? A discussion.

The above five posts strike a resonance with my own approach to our hobby: thank you for your contributions.

Al.
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Old 22nd Jul 2017, 1:58 pm   #32
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Default Re: Build your own? A discussion.

I too have built many pieces of "test equipment" in my time on this planet.. from my first crystal set, via my first scope using a VCR138a and 6SN7GT's... to my latest Antenna analyser... learning as I went. You cannot.. in my view get a better education, than building and testing some new "toy". Yes most of us have the commercial equipment that we could not do without while building our own. When I was in the TV manufacturing trade and after... we could not afford the expensive colour analyser.... on the line anyway..or the test pattern generators... and everything between... so I made them..... my favourites were the "CRT Heater meter"...and colour analysers.
I made a 4 pole filter for 2 metres, that would have been impossible to align without my home made sweep generator....... Yes.. Home construction / work builds are VERY Valid and fun.
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Old 22nd Jul 2017, 2:03 pm   #33
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Default Re: Build your own? A discussion.

I still like to build test boxes, well it was my living for over 40 years, but they were allied mostly to military stuff. But hobbies like valve amplifiers and Amateur Radio also demanded 'special-to-type' test gear too. The photos show a 4 valve monitor box which is great when working on a stereo push-pull valve amp so you can keep your eye on the little devils as they warm up . A small outboard unit is shown for plugging into an amplifier for checking bias as part of regular maintenance. The last item is a simple 1 Ohm to 1M Ohm resistance decade box. Cheaper to make than even those sold on auction sites but above all, was fun to make.
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Old 22nd Jul 2017, 2:54 pm   #34
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Default Re: Build your own? A discussion.

That resistance box is very neat. I really need to build one. I'm currently using a bodge of three potentiometers and a dpdt switch to switch a meter in and out and it's not very good
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Old 22nd Jul 2017, 3:39 pm   #35
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Default Re: Build your own? A discussion.

Quote:
and cannot handle even the simplest math!!
I was going to correct the use of math vs. maths, but as the Americans use math to mean arithmetic (I quite like the term) not now as I know some "engineers" not even up to arithmetic e.g. plugging in numbers into an equation.

Back on topic, building stuff is useful, not only for personal pride and achievement. If I interview someone (on the technical side, none of the HR carp) and they bring along a thing they made (we ask for one) and can explain it that alone is worth the fanciest bit of paper.

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Old 22nd Jul 2017, 3:40 pm   #36
JohnBHanson
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Default Re: Build your own? A discussion.

The last major item I built was a converter from a PC printer port to a microprocessor address bus. This allowed me to use real peripherals with a Z80 emulator.

I wrote a device driver under linux to allow my Z80 emulator to control the external bus. The only real shortcoming was that some Z80 peripherals monitor the Z80 instruction stream looking for reti instruction. Never did sort that problem out.

It was built on veroboard and the chips were socketed. I don't have PCB design or building facilities. However I published design notes should anyone want to reproduce it
at http://81.105.120.101/xbeaver/

It is easy to use from any application just open the device, seek to the offset corresponding to the port number and read/write as required.

Could easily be adapted to other microprocessor buses.

Building on vero meant a lot of wires had to be added so it took a long time, a shame
really.

If anyone builds a PCB version I would like a copy of the PCB in return for the device driver (Happy to pay).

The emulator is also available for download. Currently it emulates nascom/80bus as its main target. Additionally it can emulate an alphatronic/matmos PC. I have also added the intel MDS disk controllers so that ISIS can be run(!). This gives me access to PLM80 and FORTRAN.

Still having fun.....
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Old 23rd Jul 2017, 7:50 pm   #37
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Default Re: Build your own? A discussion.

Yes but make sure you dont lead yourself up the garden path. As a teenager I spent weeks trying to figure out why my home brew radio controlled transmitter field strength, as indicated by my home brew meter , went down as the areal current went up.
Finally it twigged - the field strength meter coil and capacitor put it on the 2nd or posibly 3rd harmonic. Retuned and low and behold field strength became a positive function of areal current ( indicated by a small light bulb)

So home brew test gear is fine if you have the gear or skill to test it is not leading you astray, something as a beginer I did not have!

Pete
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Old 23rd Jul 2017, 8:01 pm   #38
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Default Re: Build your own? A discussion.

To be fair, any test gear, homebrew or commercial, can give misleading results if misused, or used in a way that the designers did not anticipate, or.. I've seen the following (at least) with commercial instruments :

The DSO that would happily alias a signal higher in frequency that it was supposed to handle. Oh it gave a trace alright, just one that wasn't obviously related to the signal you were looking at.

The analogue 'scope that if you selected 'ALT' and 'Vert Mode Trigger' would give misleading phase information between the 2 input signals. In fact it was working as designed. It would select one input, wait for that signal to cross the trigger threshold, sweep (and display that signal), select the other input, wait for that to cross the trigger threshold, sweep and display it, then go round again. But as it waited for each input to cross the threshold, there was no meaningful phase relation between the 2 traces.

The electronic analogue multimeter that did not like being floated at -2kV (it was battery powered, so this was not an effect of an earthed mains supply) and gave crazy results

The DMM that was confused by strong RFI (used next to a transmitter)

The DMM on an ohms range that got confused when measuring the DC resistance of (uite large) inductors and thought they were all open-circuit.

And that's just the ones I remember. In fact I could argue that homebrew test gear is less likely to suffer from such problems as you know how it works, and you know how it was designed.
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Old 23rd Jul 2017, 11:15 pm   #39
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Arrow Re: Build your own? A discussion.

Quote:
Originally Posted by TonyDuell View Post
In fact I could argue that home-brew test gear is less likely to suffer from such problems as you know how it works, and you know how it was designed.
Agreed: in the phrase "you know how it was designed" I include the mechanical construction. The one big difference (applicable in many examples) between commercial / ready-built gear and your own is that with the latter you can incorporate maintenance (ease of) into the design. With commercial kit, that is rare - (Tektronix being one example that readily springs to mind) - and from the manufacturer's view-point I can quite understand that. It increases manufacturing cost without any immediate and obvious benefit to the buyer (well, most buyers! ) and said manufacturer would obviously prefer you to buy a replacement (when necessary) rather than you getting yours repaired - by you, the manufacturer or a third party.

Al.
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Old 24th Jul 2017, 12:34 am   #40
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Default Re: Build your own? A discussion.

I think the main problem with growing your own is that we just can't build stuff as miniaturised and well machined as the professional outfits, and for some time now, we haven't been able to build it cheaper either.

I'm reminded of an episode of 'Phoenix Nights' (Peter Kay) in which one of the characters is provided with an obviously homebrew car alarm system by the club's electrician / sparkie - in a brief scene we see the owner put the 'remote' in his pocket - built in a standard ABS project box at least three inches wide by four inches long with a big oversized button on it. I found this uncomfortably close to the truth, and quite a good observation by Kay or whoever's idea that little touch was. We've always had to put our projects in the 'next size up' project box which they will fit into. A box which is just wide enough and long enough will often be far too deep.

The main reason to build anything now is because nobody else actually makes one - for me, it's typically specific test gear or test rigs to make my job at work easier.

Last edited by SiriusHardware; 24th Jul 2017 at 12:43 am.
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