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Your Layout and Models => Electronics => Topic started by: Bealman on October 03, 2019, 06:29:37 AM

Title: Resistance Substitution Box: A Review
Post by: Bealman on October 03, 2019, 06:29:37 AM
There has been some interest lately on the SMD diodes thread about these cheap resistance substitution boxes manufactured in China. A post by ntp3 first alerted me to these (thanks, mate!  :thumbsup:), so I decided to buy one, as I thought it would be a useful bit of kit.

Mine arrived on Monday, and here, for what they're worth, are my thoughts.

First impression was that it was bigger than I thought it would be. Then I realised that this one was a different version to the one ntp3 has. Mine has an extra knob, covering the x0.1-0.9 Ohm range, hence the larger case.

(https://www.ngaugeforum.co.uk/SMFN/gallery/82/255-031019052845-82287874.jpeg)

Second impression was cheap and nasty! The plastic is poor quality - in fact, I almost thought it was second-hand! The binding posts are particularly cheap and nasty - there is no hole to pass a wire through before tightening the screw, so basically the wire will have to be wound around the post at least once before tightening in order to get a secure connection.

There are no holes on the top of the post where a banana plug could be inserted, another way of obtaining a secure connection.

The knobs are big and easy to read, and have a positive action and a satisfying click when rotated.

The instructions, of course are completely in Chinese, but Ohm's Law is the same in China I guess, so that is no big deal.

(https://www.ngaugeforum.co.uk/SMFN/gallery/82/255-031019052720-822861539.jpeg)

On a more positive note, my multimeter revealed that the accuracy of the resistors contained therein did not seem to be too bad:

All knobs set to zero gave 0.4 Ohms
1 Ohm gave 1.5
10 Ohm returned 11.4
100 Ohm returned 101.3
1 KOhm (1000 Ohms) returned 0.999K
9999.9 Ohm returned 9.94K.

I then decided to take a look inside.... big mistake!

(https://www.ngaugeforum.co.uk/SMFN/gallery/82/255-031019052847-822892230.jpeg)

Like others, I was dismayed to find that the selector switches were not wafer selector switches at all, but a jury-rigged affair of tiny SMD resistors soldered to extremely thin copper PCB tracks. When I say thin, I'm referring to the thickness of the copper tracks. I can envisage them wearing through pretty quickly if the unit has frequent use.

The rotating part of the switch is a piece of metal held in place by a spring clip, as the photo shows. Ntp3 has already noted in the diode thread that these "switches" are smothered in copious amounts of grease, and he discovered a piece of copper thread which shorted out a switch and destroyed a diode he was testing! @Malc (https://www.ngaugeforum.co.uk/SMFN/index.php?action=profile;u=497) also blew a diode by rotating a switch during testing, and recommends removing power before rotating the switches.

To add insult to injury, I couldn't get the case back together properly! Somehow I managed to lose one of the four screws, and the others had worn the plastic as I removed them, and wouldn't tighten up again!!

Judging by the teacher and blackboard on the box, along with the circuit diagrams in the instructions, I'd say this unit is meant to be used in schools to teach Physics:

(https://www.ngaugeforum.co.uk/SMFN/gallery/82/255-031019052848-822911100.jpeg)

All I can say in that regard is, that if it was connected up to the 0-15V high current power supplies I had under every bench in my lab when I was a high school Physics teacher, those SMD resistors and probably the case as well, would be TOAST!!

Anyway, wot ya pays for is wot ya get, I suppose, so I'm not really losing any sleep over the purchase. Used with care, and as Malc suggests, removing power before switching ranges, should make it a useful bit of test gear.

Comments from other users most welcome.  :beers:
Title: Re: Resistance Substitution Box: A Review
Post by: Malc on October 03, 2019, 09:32:39 AM
I was trying to find the value of resistance to use with some SMD Street lights. I wired one up to a 12v supply through the resistance box. Starting at 2k I wound the resistance up to 5K. I decided 5K was too dim, so wound it back to 4K and the led stopped working. All I can think is that somehow the box shorted out between ranges and put the full 12v across the diode. I checked all the connections, and the lamp on its own. The connections were OK, but the diode didnít conduct. Fortunately I have another 19 to play with.
Title: Re: Resistance Substitution Box: A Review
Post by: ntpntpntp on October 03, 2019, 11:54:09 AM
Yeah, as per my post last night in the SMD LED thread, the internals of the box aren't as well engineered as I'd expected, but then again the box was cheap! 

The connection posts are disappointing, I may drill them out to take a mini banana plug and also put a hole through the sides to take thin wire, or better still just replace with decent binding posts when I find a cheap pair.

Thinking about it, I may indeed have blown the LED I was playing with in the same manner as @Malc (https://www.ngaugeforum.co.uk/SMFN/index.php?action=profile;u=497) described above - changing ranges while power was being applied.  The wiper connections are "make before break" which is not ideal. The piece of copper wire/track I found inside may not have been the actual cause, but I am obviously going to go over the innards carefully and clean up the tracks.

This box will do the job for what I need now that I know its limitations.  I wonder how much a properly engineered version would cost?

Title: Re: Resistance Substitution Box: A Review
Post by: Bealman on October 03, 2019, 12:05:10 PM
Thanks for the input!  :thumbsup:


Actually, you've just put an idea into my head I'd  never even thought of until your post!

Instead of all the drilling, etc you suggest, just pull the binding terminals out all together, and replace them with decent ones from the local electronics store!

 :beers:
Title: Re: Resistance Substitution Box: A Review
Post by: DCCDave on October 03, 2019, 12:06:05 PM
This looks better built but they dare not publish a price!

https://www.fishersci.com/shop/products/eisco-6-decade-resistance-box/s96527 (https://www.fishersci.com/shop/products/eisco-6-decade-resistance-box/s96527)

Cheers
Dave
Title: Re: Resistance Substitution Box: A Review
Post by: Bealman on October 03, 2019, 12:09:56 PM
Thanks!

Wonder what it looks like inside?  ;)

Didn't like the price... A$94.

And the PSU below it.... A$439? They jest.
Title: Re: Resistance Substitution Box: A Review
Post by: Malc on October 03, 2019, 12:50:00 PM
Yeah, as per my post last night in the SMD LED thread, the internals of the box aren't as well engineered as I'd expected, but then again the box was cheap! 

The connection posts are disappointing, I may drill them out to take a mini banana plug and also put a hole through the sides to take thin wire, or better still just replace with decent binding posts when I find a cheap pair.

Thinking about it, I may indeed have blown the LED I was playing with in the same manner as @Malc (https://www.ngaugeforum.co.uk/SMFN/index.php?action=profile;u=497) described above - changing ranges while power was being applied.  The wiper connections are "make before break" which is not ideal. The piece of copper wire/track I found inside may not have been the actual cause, but I am obviously going to go over the innards carefully and clean up the tracks.

This box will do the job for what I need now that I know its limitations.  I wonder how much a properly engineered version would cost?


R.S. Do some semi pro ones for £2-300 and some better ones for £1100+
Title: Re: Resistance Substitution Box: A Review
Post by: njee20 on October 03, 2019, 01:09:40 PM
This looks better built but they dare not publish a price!

https://www.fishersci.com/shop/products/eisco-6-decade-resistance-box/s96527 (https://www.fishersci.com/shop/products/eisco-6-decade-resistance-box/s96527)

Am I missing something? Says $94 on the RH side.

6 decades of resistance should keep you going for a while though.  :confused1:
Title: Re: Resistance Substitution Box: A Review
Post by: DCCDave on October 03, 2019, 02:49:41 PM
Am I missing something? Says $94 on the RH side.

6 decades of resistance should keep you going for a while though.  :confused1:

No it's me missing the price, it was hiding behind the sign up box.

Must get some new eyes!

Cheers
Dave
Title: Re: Resistance Substitution Box: A Review
Post by: njee20 on October 03, 2019, 02:50:36 PM
Probably be cheaper than their PSUs!
Title: Re: Resistance Substitution Box: A Review
Post by: RailGooner on October 03, 2019, 02:59:57 PM
~£80 at Farnell (https://cpc.farnell.com/unbranded/model-901/model-901-resistance-box/dp/IN00081?ost=IN00081&ddkey=https%3Aen-CPC%2FCPC_United_Kingdom%2Fsearch). Or 7 decades (https://cpc.farnell.com/tenma/72-7270/resistance-decade-box/dp/IN04175?ost=IN04175&ddkey=https%3Aen-CPC%2FCPC_United_Kingdom%2Fsearch) for ~£60.
Title: Re: Resistance Substitution Box: A Review
Post by: Nigel Cliffe on October 03, 2019, 03:52:18 PM
Seems an expensive and effective way to blow up LEDs.....

This is what I've done, worked for years and years:
1 - bought a multi-packet of resistors for under £20, covering a huge range of sizes.  Mine came from Rapid, but that's because I used to live in cycling range of their trade counter, there are lots of other sources.   
2 - use a simple electronics "breadboard" to connect components - resistors, LEDs, etc. when trying out circuits.
3 - check each resistor before use with a digital multimeter.  I trust the makers, but don't trust my ability to either read resistor codes, or always put any spares back into the correctly labelled packet.  If one assumes a mistake may be made its safer.
4 - always start with a higher resistance than you might think you need.

I do have a posh lab power supply, but only because I was given it.   Before then, any old 12v PSU brick would be used.
Title: Re: Resistance Substitution Box: A Review
Post by: Steven B on October 03, 2019, 04:26:18 PM
Three potentiometers (1k, 5k and 10k) work fine for me when combined with a multimeter. They don't take up much space either.

Steven B
Title: Re: Resistance Substitution Box: A Review
Post by: Bealman on January 14, 2020, 07:42:25 AM
Thanks for the input!  :thumbsup:


Actually, you've just put an idea into my head I'd  never even thought of until your post!

Instead of all the drilling, etc you suggest, just pull the binding terminals out all together, and replace them with decent ones from the local electronics store!

 :beers:

Finally got round to doing that today (well, attempting that today).

Turns out nowt's easy. Bloody holes need drilling out as the new binding posts have a wider diameter than the existing hole.

No big deal really, but since the new kitchen came along, my workbench is the one and only table (note table cloth and circular table edge, not good).

I gave up on it and put it back together!

(https://www.ngaugeforum.co.uk/SMFN/gallery/86/255-140120073441-86088253.jpeg)

Title: Re: Resistance Substitution Box: A Review
Post by: Bealman on January 22, 2020, 06:28:28 AM
Me being me, and looking for an easy way out, I saw this at the local Jaycar store for ten bucks. I used me reward points, so I've got yet another bit of Chinese product in me toolbox.

Unfortunately, the spade connectors are a bit on the big side for the terminals on the Chinese resistor box!

There's no free lunch  ;)

(https://www.ngaugeforum.co.uk/SMFN/gallery/86/255-220120062150-864681011.jpeg)
Title: Re: Resistance Substitution Box: A Review
Post by: keerout on January 22, 2020, 05:46:37 PM
 TANSTAAFL !  :no:

Gerard  :wave:
Title: Re: Resistance Substitution Box: A Review
Post by: Railwaygun on January 22, 2020, 08:12:42 PM
There ain't no such thing as a free lunch

Title: Re: Resistance Substitution Box: A Review
Post by: ntpntpntp on January 23, 2020, 08:55:44 PM
** A WARNING ***   

Just been playing with my resistance box and some 12V strip LEDS, working out what additional resistance to add to each strip to tone them down to the effect I'm after for my loco sheds.

The design of box I have shorts out to 0 when moving between 4 and 5 on the dial!  I witnessed it on the x1000, x100 and x10 dials, and pretty sure the x1 does it too although changing by 5 ohms is difficult to see the difference - I didn't bother to get my multimeter out.

This confirmed what I thought might be the case as I managed to blow some other LED mast lights a few weeks ago.

What a nuisance, still at least I know to avoid that in future.
Title: Re: Resistance Substitution Box: A Review
Post by: Malc on January 25, 2020, 05:09:05 PM
Yes, I too found this out the hard way. Fortunately I only blew one street light.
Title: Re: Resistance Substitution Box: A Review
Post by: Bealman on May 22, 2020, 04:00:18 AM
It's all sort of academic to me now.... if anyone has been looking at my layout thread, they'll know I've been rummaging around under the layout lately.

I turned up this:

(https://www.ngaugeforum.co.uk/SMFN/gallery/93/255-220520035005-938441177.jpeg)

A resistance wheel! Forgot I had it. Discrete resistors inside, too. Here it is on the one Meg setting, reading 0.974 Meg.
Title: Re: Resistance Substitution Box: A Review
Post by: Malc on May 22, 2020, 09:06:22 AM
A proper bit of kit.
Title: Re: Resistance Substitution Box: A Review
Post by: Lawrence on May 22, 2020, 09:13:42 AM
You only get what you pay for as you say George, there is always this option https://uk.rs-online.com/web/p/decade-boxes/7921976/
I was trying to get one for work but we had to settle on a slightly lesser model around the £250 mark.
I would hate to try to teach you to suck eggs but wanted to mention one thing, when you were measuring at 0 Ohm did you connect your leads together and zero your meter first? Budget mulitmeters (and associated leads etc) are much like budget decade resistance boxes  ;)
Title: Re: Resistance Substitution Box: A Review
Post by: tutenkhamunsleeping on May 22, 2020, 09:14:13 AM
No ohm should be without one :-[
Title: Re: Resistance Substitution Box: A Review
Post by: Bealman on May 22, 2020, 09:17:41 AM
About A$45 in the local electronics store. After much head-scratching as to where it came from, I worked out that I'd ordered it way back for the science department at school. After realising there was no way it would handle the currents involved in high school experiments, it languished for years in my prep room.

Somehow it ended up in my box of stuff I salvaged from the place when I retired  :whistle:
Title: Re: Resistance Substitution Box: A Review
Post by: Malc on May 22, 2020, 09:28:56 AM
Stolen goods then?
Title: Re: Resistance Substitution Box: A Review
Post by: Bealman on May 22, 2020, 10:30:09 AM
Missing in inaction.  ;)
Title: Re: Resistance Substitution Box: A Review
Post by: andy911john on May 24, 2020, 05:35:42 PM
I found this on-line.  Looks like a reasonable compromise.   Switches rather than questionable rotary make before break. 

https://weisd.com/products/2300-elenco-rs-500-resistance-decade-box?gclid=EAIaIQobChMIq7rM5_XM6QIVEfDACh07YAlLEAQYFCABEgLeBfD_BwE
Title: Re: Resistance Substitution Box: A Review
Post by: ntpntpntp on May 24, 2020, 05:46:19 PM
@andy911john (https://www.ngaugeforum.co.uk/SMFN/index.php?action=profile;u=8320)

Manual for the Elenco RS500. 

https://www.elenco.com/wp-content/uploads/2011/03/RS-500_RevE.pdf (https://www.elenco.com/wp-content/uploads/2011/03/RS-500_RevE.pdf)
Title: Re: Resistance Substitution Box: A Review
Post by: themadhippy on May 24, 2020, 06:39:51 PM
only problem is you have to fink a bit  to get some values,making your own is very easy,especially if you use these type of switches
(https://i.stack.imgur.com/AcA5z.jpg)

but make sure to get the decimal version,the bcd version aint no good as it outputs  binary
Title: Re: Resistance Substitution Box: A Review
Post by: The Q on May 25, 2020, 08:02:02 AM
You only get what you pay for as you say George, there is always this option https://uk.rs-online.com/web/p/decade-boxes/7921976/

Not too bad I suppose , if you check the values before use,  we have 3 of these https://eu.flukecal.com/products/electrical-calibration/bench-multimeters/8558a-8-5-digit-multimeter, and three of its predecessors available for me to use at work.

If you wanted us to calibrate resistance the we measure over most values  to 0.1 parts in a million, though our uncertainty is about 0.3ppm at 10k Ohm,  and about 18ppm at 1G Ohm.   :D . Though if you contact the National Physical Laboratory at Teddington,  they are even more accurate ( at vast expense) .
We actually do calibrate some cropico equipment to a slightly lower standard in the outer lab.

PS I'm not saying who I work for because I like to take the P**s out of the management occasionally and I've been recalled from furlough Next Week.
Title: Re: Resistance Substitution Box: A Review
Post by: ronp849 on May 25, 2020, 12:44:38 PM
If it is just to find a resistor for a suitable LED brilliance, I run an led from a constant current power supply, (Cheaper than some of the resistance boxes posted here :laugh:) and then I calculate what resistance I need to deliver that current. I have not used a resistance box since my school days in the last century.
Title: Re: Resistance Substitution Box: A Review
Post by: Bealman on June 04, 2020, 11:58:40 PM
The June edition of Aussie magazine Silicon Chip has a new design which looks most interesting. They say it was inspired by the very resistance wheel in my earlier post, which has now been discontinued.

Their new design though is an RCL box all in one, with a colour touchscreen, and fitted into a compact UB3 jiffy box.

It uses Geoff Graham's Micromite BackPack (for those who don't know, the Micromite is an Aussie success story, and utilises a very comprehensive version of BASIC).

The RCL box uses 30 relays!

This looks like a good bit of gear for circuit prototyping, providing as it does, inductance and capacitance as well as resistance substitution.

It naturally uses SMD components, and the relays are SMD too (Panasonic TQ2SA-5V).

Construction details to follow in July.
Title: Re: Resistance Substitution Box: A Review
Post by: themadhippy on June 05, 2020, 12:53:01 AM
Quote
Geoff Graham's Micromite
How do i put Bealman on ignore? Just as i was getting over my  addiction to ardunios  he  mentions a 3 quid chip that can run basic  has 19 i/o lines and is in stock with RS who deliver next day . :censored:
Title: Re: Resistance Substitution Box: A Review
Post by: Bealman on June 05, 2020, 12:56:54 AM
I must admit I have no experience with them, but I'm thinking of ordering a Colour Maximite for a play around. I'm a lot more comfortable with BASIC than I am with C.
Title: Re: Resistance Substitution Box: A Review
Post by: Bealman on June 05, 2020, 01:00:26 AM
Point of information for UK members: most Silicon Chip projects end up in the UK mag Everyday Electronics, and parts and kits are available through that magazine.
Title: Re: Resistance Substitution Box: A Review
Post by: The Q on June 05, 2020, 02:33:38 PM
Point of information for UK members: most Silicon Chip projects end up in the UK mag Everyday Electronics, and parts and kits are available through that magazine.
Thats a blast from the past I haven't read EE in 40 years, since I started doing the stuff for a job..

Ah I see EE hasn't existed in it's own right since 1997, it was merged into Practical Electronics, which dropped Everyday back out of the title in 2019..
Title: Re: Resistance Substitution Box: A Review
Post by: themadhippy on June 05, 2020, 03:19:07 PM
Quote
Thats a blast from the past I haven't read EE in 40 years
If you want to catch up theirs plenty of old issues at https://worldradiohistory.com/Everyday_Electronics.htm
Title: Re: Resistance Substitution Box: A Review
Post by: Bealman on June 06, 2020, 01:01:09 AM
Point of information for UK members: most Silicon Chip projects end up in the UK mag Everyday Electronics, and parts and kits are available through that magazine.
Thats a blast from the past I haven't read EE in 40 years, since I started doing the stuff for a job..

Ah I see EE hasn't existed in it's own right since 1997, it was merged into Practical Electronics, which dropped Everyday back out of the title in 2019..

You are quite correct of course, but I must admit that until your post, I never noticed that in the newsagents!!

Most of the articles are still from the Aussie source, though.  :thumbsup:

No doubt the RCL box will show up in there soon. I'm very impressed with the design - it even has a 'ramp' feature built into the software to automatically select a substitute without damaging the circuit.

The relays combine RCL values within the box to obtain other values. Clever!
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