Author Topic: Cheap Chinese Decade Resistor box  (Read 672 times)

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Offline ciccio

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Cheap Chinese Decade Resistor box
« on: September 20, 2020, 08:13:04 pm »
[attach=4]Sorry for the bad quality of the writing ad of attached images,
but I'm  out of exercise, being returned recently from hospital. And computers and photo camera are like little greeen aliens, now.
I wanted to build a 4 decade resistor box (0 to 10 Kohms 0,1 Ohms resolution,  , and began searching   ALIEXPRESS for the necessary components,  10 position rotary switches, knobs and a suitable enclosure, then I found one ready assembled, at the very low price of 11,05 Euro
                                                                             
It is not bad,and came in a suitable mailingbox, which bears the manufacturer’s name  : JiaoXueyiqi, complete with an 8 pages  user’s manual (in Chinese),  with schematic and application instructions.
I could not find any technical specification (tolerance, andpower handling: there is an indication of maximum current allowable).                                                                                                     
It is obviously intended for educational use
 
The attached images show the product, which is available here :
ttps://login.aliexpress.com/?returnUrl=https%3A%2F%2Ftrade.aliexpress.com%2Forder_detail.htm%3Fspm%3Da2g0s.9042311.0.0.22254c4duy27Rp%26orderId%3D3005125109566444%26tsp%3D1600627413628]]ttps://login.aliexpress.com/?returnUrl=https%3A%2F%2Ftrade.aliexpress.com%2Forder_detail.htm%3Fspm%3Da2g0s.9042311.0.0.22254c4duy27Rp%26orderId%3D3005125109566444%26tsp%3D1600627413628                                                                         
                                                                                                                                                                                                                                   
The first thing I noticed are the  binding posts, which  have no 4 mm hole for a banana Plug.
They will be replaced soon, with little effort.                                                               
The circuit is a single side PCB where the  resistors, which seem standard 1206  SMD components, are soldered (hey seeem having been hand soldered, )
The Switches’s contacts seem made with steeel foil (No silver here…)  plated with what seem tin (I could solder a wire to it,  so it must be tinned).
The schematic is different from those I’ve seen in other decade boxes, because they used less resistors as you can see:
Looking at the x 1K decade, instead of 10 1K resistors wired in series (one per position) here we see a two pole switch and a 5K resistor which,on positions 6, 7, 8 and 9, connects to the other section’ common.  Four 1K resistors are wired  to positions, 1, 2, 3, 4, , so  6K is obtained with 5 K + 1 K, 8 K  = 5K +  3 x1K                                                                                                       

                                                                             
It is not bad,and came in a suitable mailingbox, which bears the manufacturer’s name  : JiaoXueyiqi, complete with an 8 pages  user’s manual (in Chinese),  with schematic and application instructions.
I could not find any technical specification (,tolerance,and powr handling: there is an indication of maximum curent allowable).                                                                                                     
It is obviously intended for educational use
 
The attached images show the product, which is available here :
https://login.aliexpress.com/?returnUrl=https%3A%2F%2Ftrade.aliexpress.com%2Forder_detail.htm%3Fspm%3Da2g0s.9042311.0.0.22254c4duy27Rp%26orderId%3D3005125109566444%26tsp%3D1600627413628                                                                           
                                                                                                                                                                                                                                   
The first thing I noticed are the  binding posts, which  have no 4 mm hole for a banana Plug.
They will be replaced soon, with little effort.                                                               
The circuit is a single side PCB where the  resistors, which seem standard 1206  SMD components, are soldered (hey seeem having been hand soldered, )
The Switches’s contacts seem made with steeel foil (No silver here…)  plated with what seem tin (I could solder a wire to it,  so it must be tinned).
The schematic is different from those I’ve seen in other decade boxes, because they used less resistors as you can see:
Looking at the x 1K decade, instead of 10 1K resistors wired in series (one per position) here we see a two pole switch and a 5K resistor which,on positions 6, 7, 8 and 9, connects to the other section’ common.  Four 1K resistors are wired  to positions, 1, 2, 3, 4, , so  6K is obtained with 5 K + 1 K, 8 K  = 5K +  3 x1K                                                                                                       
Interesting, they saved 20 resistors ( 4 decades  per 5 resistors each) in the whole box…
IF I want better specifications , I can easilyreplace the resistors with better ones, 

I tested yhe unit using a My UNI-T UT 61 , and It seem to work according to the specifications.
The switches have  a nice feel, and a good click..
The contacts work against the coppers surface of the  PCB.
There is misterious transparent “grease” covering the contact area. I did not understood it’s nature and funcction: it seeems glycerine,
                                                                 
                                                                                       
                                                                         


                                         
« Last Edit: September 21, 2020, 12:45:55 pm by ciccio »
Strenua Nos Exercet Inertia
I'm old enough, I don't repeat mistakes.
I always invent new ones
 
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Online ledtester

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Re: Cheap Chinese Decade Resistor box
« Reply #1 on: September 29, 2020, 02:49:29 am »
Happen to run across the German language review:

https://youtu.be/Yg2NDJMQ6Ks

At 1:37 they offer their own explanation of the grease... using the automated translation it goes like this:

Quote
... By the way these are not scratches on the surface of the circuit board, but rather one layer of fat that was probably applied with the intention that the sander turns more easily and does not see through the circuit board too quickly. ...

Their case screw posts were also broken on delivery.

At 3:19 the video shows the resistance reading for each dial setting (50 settings, 10 per dial).
 

Offline ebclr

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Re: Cheap Chinese Decade Resistor box
« Reply #2 on: September 29, 2020, 05:15:14 am »
That trick to save some resistors, will create quad error due contact resistance and 1/8 endurance , due the low quality of the switches, Does not have sense to do that to save 5 SMD resistors
« Last Edit: September 29, 2020, 05:17:14 am by ebclr »
 

Offline bob91343

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Re: Cheap Chinese Decade Resistor box
« Reply #3 on: September 29, 2020, 05:35:45 am »
You can estimate the power rating from the size of the resistors.  If they are SMD they are very low power.

It would be wise to measure the zero resistance to see how small it is, and to measure the inductance if it's made from wire resistors.  Or the capacitance, if made from film.
 

Offline JimKnopf

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Re: Cheap Chinese Decade Resistor box
« Reply #4 on: September 29, 2020, 10:41:36 am »
I bought this box 2 years ago and was a bit annoyed about the quality. Technically it looks like it is from Mao's bygone days.
No Banana plugs, not very accurate.

I build my own resistor decade box like this one https://github.com/JimKnopfIoT/Resistor-decade and this one https://www.eevblog.com/forum/projects/diy-cheap-resistor-decade-substitution-box/?PHPSESSID=7v2kdh9d73d8ec888ailj6ch51

I now have two versions. One with resistors like the one's on the images in the links above and one with SMD resistors. They SMD resistors are very accurate.  There are 10 pushwheels, starting from the right side, with 0.1 ohms. The second wheel is just a "," separator, then 1, 10, 100, 1k, 10k, 100k,1M, 10M ohms.
Easy to build and very cheap.

https://de.aliexpress.com/item/1804257049.html?spm=a2g0x.search0104.3.3.77714fd8n619wE&ws_ab_test=searchweb0_0,searchweb201602_1_10065_10068_10547_319_317_10548_10696_10084_453_10083_454_10618_10304_10307_10820_10821_537_10302_536_10843_10059_10884_10887_321_322_10103,searchweb201603_52,ppcSwitch_0&algo_expid=74f2ba4e-8ce3-44fa-b0db-6c3282b49dbd-0&algo_pvid=74f2ba4e-8ce3-44fa-b0db-6c3282b49dbd&transAbTest=ae803_5

Use quality of your choice for the resistors.
i keep the chinese resistance decade box as an example of how not to do it.
 

Offline Doctorandus_P

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Re: Cheap Chinese Decade Resistor box
« Reply #5 on: September 29, 2020, 01:26:02 pm »
The grease may also be silicone based.

A bit of lubrication may improve the "feel" of the switch, and it reduces wear on the contacts.
It also covers the copper contacts and prevents them from oxidizing.
I've also seen this used in rotary switches of multimeters.
 
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Offline JoeyG

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Re: Cheap Chinese Decade Resistor box
« Reply #6 on: September 29, 2020, 01:51:43 pm »
use  jumpers anyone  https://ebay.us/URqoW4
 


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