Cheap Chinese Decade Resistor box - Page 1
Forum section: electronics / testgear

author: ciccio
author_rank: Frequent Contributor
timestamp: September 20, 2020, 08:13:04 pm
content: 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 EuroIt 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 useThe 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%3D1600627413628The 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 x1KIt 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 useThe 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%3D1600627413628The 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 x1KInteresting, 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,

author: ledtester
author_rank: Super Contributor
timestamp: September 29, 2020, 02:49:29 am
content: Happen to run across the German language review:https://youtu.be/Yg2NDJMQ6KsAt 1:37 they offer their own explanation of the grease... using the automated translation it goes like this:QuoteTheir 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).

author: ebclr
author_rank: Super Contributor
timestamp: September 29, 2020, 05:15:14 am
content: 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

author: bob91343
author_rank: Super Contributor
timestamp: September 29, 2020, 05:35:45 am
content: 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.

author: JimKnopf
author_rank: Frequent Contributor
timestamp: September 29, 2020, 10:41:36 am
content: 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 onehttps://github.com/JimKnopfIoT/Resistor-decadeand this onehttps://www.eevblog.com/forum/projects/diy-cheap-resistor-decade-substitution-box/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_5Use quality of your choice for the resistors.i keep the chinese resistance decade box as an example of how not to do it.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 29, 2020, 01:26:02 pm
content: 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.

author: JoeyG
author_rank: Regular Contributor
timestamp: September 29, 2020, 01:51:43 pm
content: use jumpers anyonehttps://ebay.us/URqoW4