Test Equipment Anonymous (TEA) group therapy thread

[Specmaster]

I wouldn’t pay $50 for it. $1/MHz is a sensible price.

I think the last scope I had of that bandwidth I paid £5 (about $6 or $7) and that had a box, probes, manuals and was dual trace.

Sounds like a good rule of thumb, we get stiffed pretty badly here in Aus tho so everything is over priced.

Thank dog Amazon is finally launching properly here next week!

I agree, going rate in Australia is much the same as the UK, remember Daventry doing a blog on getting a 20Mhz CRO for around $20 and dual trace to boot.

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I agree, going rate in Australia is much the same as the UK, remember Dave doing a blog on getting a 20Mhz CRO for around $20 and dual trace to boot.


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[Specmaster]

Update on my thumbwheel switches, seller asked for a photo, which I sent him along with a photo of his own ebay page showing the correct terminals. I also pointed out that not only was the coding wrong but the size of the switch, as I ordered KSA-2 ones which are 31mm x 10mm x 40mm and they supplied KM2 type at 22mm x 8mm x 40mm 

This morning I have an email stating that they are very sorry for trouble and given me full refund, so why not send the correct ones out again 

[Mr. Scram]

Update on my thumbwheel switches, seller asked for a photo, which I sent him along with a photo of his own ebay page showing the correct terminals. I also pointed out that not only was the coding wrong but the size of the switch, as I ordered KSA-2 ones which are 31mm x 10mm x 40mm and they supplied KM2 type at 22mm x 8mm x 40mm 

This morning I have an email stating that they are very sorry for trouble and given me full refund, so why not send the correct ones out again 

I guess they don't have the correct ones?

[Specmaster]

Update on my thumbwheel switches, seller asked for a photo, which I sent him along with a photo of his own ebay page showing the correct terminals. I also pointed out that not only was the coding wrong but the size of the switch, as I ordered KSA-2 ones which are 31mm x 10mm x 40mm and they supplied KM2 type at 22mm x 8mm x 40mm 

This morning I have an email stating that they are very sorry for trouble and given me full refund, so why not send the correct ones out again 

I guess they don't have the correct ones?

According to his Ebay shop he does, but not as KSA-2, but as KM2, same size but half the price of the KSA-2s and in grey not black.

I did say in my email, that if he did not have the KSA-2 in black, then grey would be OK, also if he doesn't have any at all, that I'd be happy to accept 2 x KM2, in any colour as long as they were decimal coded. 

It must be cheaper to send out replacements then refunding money??  Maybe he has discovered that all of his stock is infact BCD type after all but it would have been preferable to have been told that. 

[bd139]

I think Wun Hung Lo probably doesn't know the difference because he has to stick random shit in bags quickly from 25 different ebay stores. They're probably in a big cardboard box next to some T-shirts and some dangerous lanterns. Refund is easier because he wants you to go away.

[djos]

I wouldn’t pay $50 for it. $1/MHz is a sensible price.

I think the last scope I had of that bandwidth I paid £5 (about $6 or $7) and that had a box, probes, manuals and was dual trace.

Sounds like a good rule of thumb, we get stiffed pretty badly here in Aus tho so everything is over priced.

Thank dog Amazon is finally launching properly here next week!

I agree, going rate in Australia is much the same as the UK, remember Daventry doing a blog on getting a 20Mhz CRO for around $20 and dual trace to boot.

Sent from my SM-J510FN using Tapatalk

I agree, going rate in Australia is much the same as the UK, remember Dave doing a blog on getting a 20Mhz CRO for around $20 and dual trace to boot.


Sent from my SM-J510FN using Tapatalk

Not in Melbourne in the last 6 months unfortunately, I see no name crap listing for $150 plus and decent stuff gong for $300 plus. 

[Specmaster]

I think Wun Hung Lo probably doesn't know the difference because he has to stick random shit in bags quickly from 25 different ebay stores. They're probably in a big cardboard box next to some T-shirts and some dangerous lanterns. Refund is easier because he wants you to go away.

I think you're right. However, just found another seller who claims to have the right ones in stock (KSA-2 and in black) and his photos clearly show the correct terminations and as an added bonus, comes with the 2 end mounted spring loaded mounting clips to retain them in the panel, bobby dazzler, and half the fucking price as well. Just ordered 2 of them suckers, so if the switches are a bit dicky, I'll have some spares. 

[Mr. Scram]

I think you're right. However, just found another seller who claims to have the right ones in stock (KSA-2 and in black) and his photos clearly show the correct terminations and as an added bonus, comes with the 2 end mounted spring loaded mounting clips to retain them in the panel, bobby dazzler, and half the fucking price as well. Just ordered 2 of them suckers, so if the switches are a bit dicky, I'll have some spares. 

Now you're just making yourself look like a greenhorn eBay jockey. Anyone half decent would've found that one in the first place. 

[Specmaster]

I think you're right. However, just found another seller who claims to have the right ones in stock (KSA-2 and in black) and his photos clearly show the correct terminations and as an added bonus, comes with the 2 end mounted spring loaded mounting clips to retain them in the panel, bobby dazzler, and half the fucking price as well. Just ordered 2 of them suckers, so if the switches are a bit dicky, I'll have some spares. 

Now you're just making yourself look like a greenhorn eBay jockey. Anyone half decent would've found that one in the first place. 

Except of course they weren't advertised at that time 

[Mr. Scram]

Except of course they weren't advertised at that time 

Excuses too. Tisk tisk.

[Specmaster]

Except of course they weren't advertised at that time 

Excuses too. Tisk tisk.

What ever, lets wait what actually turns up this time, anyone want to take a shot at guessing?

[Mr. Scram]

What ever, lets wait what actually turns up this time, anyone want to take a shot at guessing?

I've had some bad luck with China lately. I had a good run of about a year or so of almost everything turning up and being what it should be, but now issues seem more common.

[bd139]

I reckon you'll receive an inflatable Mr Blobby from Noel's House Party.

Bad luck with China here recently. Ordered about 10 things (all under £1) for a laugh the other day. Will see what turns up.

[Specmaster]

What ever, lets wait what actually turns up this time, anyone want to take a shot at guessing?

I've had some bad luck with China lately. I had a good run of about a year or so of almost everything turning up and buying what it should be, but now issues seem more common.

Yep, been there with Banggood, but lately they seem to have got their act together more.

[Specmaster]

I reckon you'll receive an inflatable Mr Blobby from Noel's House Party.

Bad luck with China here recently. Ordered about 10 things (all under £1) for a laugh the other day. Will see what turns up.

With any luck you'll end with Noel Edmunds himself to go with my Blobby Blobby 

[Specmaster]

Question for you all, with this bcd thumbwheel, I was thinking of making it into a capacitance decade box but given that the switches are not really suitable for carrying much current, what voltage rating would anyone suggest I use for the caps and I'm guessing that its most suitable for SMD devices. 

[bd139]

Can't say I've ever had the need for a capacitance box. Usually the things you need them for are adding miller capacitance which is pointless doing with a cap sub box because the parasitic inductance is huge (hello unexpected colpitts and VHF oscillation), RC timing (calculation is pretty accurate for this and it's cheaper to trim the resistor!), filters (again calculation rules!), stuffing capacitive loads on things (just solder a cap or a bit of coax across the output and snip it at the desired length ).

If you decide to proceed you have a few options and ranges:

Ok stability. 100pF->100nF - Use X7R rated MLCC capacitors. Good to 50v

High stability. 100pF->100nF - Use C0G rated MLCC capacitors. Good to 50v

High stability, low leakage. 1nF -> 1uF - Use film caps (TH). Vishay 1813's are nice but LARGE. Chap polybox film caps are ok too. Even mylar green blobs aren't that bad apart from microphonics. Good up to 200v or so (switches will die before that).

MLCC SMD caps and TH caps are the same parts. If you crack the epoxy on an MLCC TH capacitor there's an SMD one inside it with legs soldered on dipped in epoxy.

[Specmaster]

Can't say I've ever had the need for a capacitance box. Usually the things you need them for are adding miller capacitance which is pointless doing with a cap sub box because the parasitic inductance is huge (hello unexpected colpitts and VHF oscillation), RC timing (calculation is pretty accurate for this and it's cheaper to trim the resistor!), filters (again calculation rules!), stuffing capacitive loads on things (just solder a cap or a bit of coax across the output and snip it at the desired length ).

If you decide to proceed you have a few options and ranges:

Ok stability. 100pF->100nF - Use X7R rated MLCC capacitors. Good to 50v

High stability. 100pF->100nF - Use C0G rated MLCC capacitors. Good to 50v

High stability, low leakage. 1nF -> 1uF - Use film caps (TH). Vishay 1813's are nice but LARGE. Chap polybox film caps are ok too. Even mylar green blobs aren't that bad apart from microphonics. Good up to 200v or so (switches will die before that).

MLCC SMD caps and TH caps are the same parts. If you crack the epoxy on an MLCC TH capacitor there's an SMD one inside it with legs soldered on dipped in epoxy.

Therein lays my problem, as you know, I'm much more of a low frequency man so my needs wouldn't be as critical as those for you but then as you rightly said the switches aren't up to the kind of currents required for smoothing on larger caps that I'd come across more in my line of current involvement with electronics so maybe a cap box is not such a good idea.

So I'm back at the wondering stage of could I use a bcd switch bank for?

[bd139]

Haven't thought it through but can you use a BCD switch to build an R2R DAC? If so you could build a programmable voltage source. This can be used for all sorts of things from programmable current sources (the basis of accurate wave and pulse generators) to current calibrators etc.



You can stack these end to end in different ranges so 100, 200, 400, 800 ohms etc.

Use it with the following, replacing the 1mA current source into the capacitor with a opamp based current source driven from the above and you have a programmable triangle wave (and square wave) generator:



Images shamelessly stolen from the Art of Electronics Laboratory manual (1st edition book)

[tggzzz]

Ok stability. 100pF->100nF - Use X7R rated MLCC capacitors. Good to 50v

... for some definition of "OK" that I'm not familiar with. Look at the tempco and capacitance vs voltage. Some lose 80% of their capacitance at the rated voltage!

Personally I think this discussion should be (and is worth) shunting off into a separate thread; it doesn't have much to do with TEA.

[bd139]

Ok as in that cleverly disguised word "shit" ... Definitely agree with OT.

Back on topic. Just completed cal of the 2225 and it's spot on now. Managed to crisp up the trace even further with astig and grid bias pots. Very happy!

[Specmaster]

Ok as in that cleverly disguised word "shit" ... Definitely agree with OT.

Back on topic. Just completed cal of the 2225 and it's spot on now. Managed to crisp up the trace even further with astig and grid bias pots. Very happy!

Hmm, thought it was on topic, it's producing a test item surely?

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[Specmaster]

Ok as in that cleverly disguised word "shit" ... Definitely agree with OT.

Back on topic. Just completed cal of the 2225 and it's spot on now. Managed to crisp up the trace even further with astig and grid bias pots. Very happy!

Hmm, thought it was on topic, it's producing a test item surely?

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Just replaced a tant in scope calibrator so I'll be bringing my goldstar scope back to the bench and finishing the calibration on it.

Good news about your 2225 bd139.

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[tggzzz]

Ok as in that cleverly disguised word "shit" ... Definitely agree with OT.

Back on topic. Just completed cal of the 2225 and it's spot on now. Managed to crisp up the trace even further with astig and grid bias pots. Very happy!

Hmm, thought it was on topic, it's producing a test item surely?

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In that case much of the metrology and repair forums could be subsumed into this thread!

Have a look at the first posting in this thread, to see why this thread has lasted so long.

Sent from my PC using a keyboard without Whackachatter.

[SparkyFX]

I am about to build a few decade boxes as well (and got those cheap decimal and BCD thumbwheels on order, 150mOhms, KM2), which is why i am interested in these posts. I second that the result will be some test equipment. Manufacturer: oneself, precision: if you can afford it. :-) But i´ve got no problem to have it split into another thread if a moderator sees fit.

Haven't thought it through but can you use a BCD switch to build an R2R DAC?

Thought of that too, but it won´t be free of potential (without batteries or isolation or ...) and requires supply voltage, that rules it out for me as a general purpose box you just hook up somewhere into the circuit. One of my adjustable power supplies is always usable in that way as well.

Soldering 9 resistors of the same value in a decimal thumbwheel is relatively straightforward, otoh instead of several single values with high precision. Money wise you rather loose, the price is almost identical between decimal/bcd thumbwheel switches, the single resistors make it a bit more expensive and should something break you need to have that value in that precision. As for the precision: if one really wants to get that last 0.1%: you can still pre select parts and choose the proper ones, like in


and




And just for the thrill of automating test equipment:
Recently i was playing around with connecting to the RS232 of one older cheap multimeter, the output is quite decodable, shouldn´t be too hard to write some script to filter the lowest point in a measurement and recording that value. I also got a more precise Peaktech 3440 with 4,5 digits/0.01Ohm Resolution, but it is Bluetooth-enabled. Still need to check how to issue the discover and connect of the dongle to get it running, hints greatly appreciated.

Found the VISA docs for python (pyVisa), that would be something to get a bench multimeter for, a Siglent SDM3065X struck my attention so far.

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