EEVblog #1272 - Mailbag

[EEVblog]

More Mailbag!
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SPOILERS:
Vintage Tek Scopes
2:57 8 Cent Touch Sensor Chip TTP223 from TonTek: https://lcsc.com/products/Touch-Screen-Controller-ICs_902.html?q=ttp223
9:08 DefPom's new open source BOM tool MyPartsBin: https://mypartsbin.com/
https://www.youtube.com/user/TheDefpom
Casio FX-730P Calculator
11:49 FREE Multimeters went to a good cause, and Amazon Returns
14:07 CB2 Micro Kit: http://cb2.qrp.gr/
17:02 50,000 Count $150 CEM DT-9969 / PDI DM-950BT
https://pdimeters.com/products/Electronic-and-General-Purpose/DM950BT.php
The Church Of Tesla: https://www.churchoftesla.org/
31:34 Vintage Telecom telephone gear, and mechanical counters.
41:39 PCB piezotronics RS Technologies Torque sensing wrench
46:58 Big Arse Variable Resistor
48:27 JYE Tech DSO138 Oscilloscope Kit

[Flappy]

The Telecom Telemeter was used to indicate phone call charges.  The exchange would send a "meter pulse" down the line to make the meter tick over.  The meter pulses were ~100 V AC 50Hz with a 220ms duration.  The signal was sent on both wires with respect to ground so not to be audible during calls.
 Often installed in motels so the motel would know how much to charge guests for the phone calls they made from their rooms. 

[Flappy]

The 2W VFHA (two wire voice frequency hybid amplifer) was installed in the exchange on long phone lines.  It could amplify in both directions simultaneously.  There are adjustments for gain, equalization, and impedance matching. 

[Flappy]

The two wire voice switch amplifier could only amplify in one direction at a time.  It would switch to whoever on the call was talking at the time. 

A group of Telspec employees left to form their own company.  Extel. 

[Flappy]

The AVFHA Adaptive Voice Frequency Hybrid Amplifier could automatically adjust it's termination network.  It would generate a short burst of noise at the start of the call and listen for reflections. 

[Flappy]

The SLE Subscriber Loop Extender would boost the DC part of the phone service.  The DC current flow would tell the telephone exchange that the customer would like some dial tone and probably will be dialling some digits.  The SLE was often used in conjunction with a VFHA. 

[johnlsenchak]

I worked  for  a telecommunication  company  that  manufactured  PBX  system  for large  scale  companies  many years  ago .   That audio   telcom  board,  looks to me   like  it  sends audio  between   telephone  handsets  used  for VOX  purposes  through the speakers inside the  units.    It's usually  between multiple  "telecom lines"  connected  to   telephone  handsets  like in  a  conference  configuration.   Those PC  boards  are  real old  school  telephone   analog  PBX  systems that are not used  anymore  due to VOIP  technology

[Peabody]

Re the DSO138 kit scope, when last I heard, Banggood sold authentic JYETech stock.  Actually the one to get is the DSO150, which is a newer design with a rotary encoder and slightly better specs.  Looks like the DSO150 kit version is about $16, plus you need to buy a real scope probe (comes with alligator clip probe) and a 9V power supply.  Assembled, with a real probe, but still no power supply, is about $23.  The fun part is converting them to battery powered, so another maybe $12 for a charger module, boost converter module and the battery.  There's a long thread on the JYETech forum about this battery conversion, with everybody, including me, giving their version of how to do it.

It has been surprising to me how useful the DSO150 has been.  You would think it's too slow to be of any real use, but there are a lot of things like steppers, servos, PWM, various serial protocols, audio, and so forth, that these little scopes deal with just fine.  And it's also useful to to have a battery-powered scope that isn't referenced to anything.  So if you want to measure the voltage drop across a mosfet, you don't have to worry about where ground is, or blowing anything up.  But probably because of the small capture memory, I believe triggering only works at 20ms and faster.

In the video, I think Dave has the 138 on Auto mode, and I think it wouldn't wander if it was in Normal mode.

And for the adventurous, there's a two-channel version (the Wave 2) for $65 plus a battery.  Does X/Y, has a function generator, etc., but basically the same specs.

[johnh]

There were several version of the private meters.  50Hz longitudinal  pulse or 12Khz tone.

The 50Hz meters were pulled out when they started removing the loading on the cable pairs.

Some version the customers could reset the total count. There was one version  were the total count couldn't be reset, these were used when there was a billing dispute.

[thm_w]

Re the DSO138 kit scope, when last I heard, Banggood sold authentic JYETech stock.  Actually the one to get is the DSO150, which is a newer design with a rotary encoder and slightly better specs.  Looks like the DSO150 kit version is about $16, plus you need to buy a real scope probe (comes with alligator clip probe) and a 9V power supply.  Assembled, with a real probe, but still no power supply, is about $23.  The fun part is converting them to battery powered, so another maybe $12 for a charger module, boost converter module and the battery.  There's a long thread on the JYETech forum about this battery conversion, with everybody, including me, giving their version of how to do it.

It has been surprising to me how useful the DSO150 has been.  You would think it's too slow to be of any real use, but there are a lot of things like steppers, servos, PWM, various serial protocols, audio, and so forth, that these little scopes deal with just fine.  And it's also useful to to have a battery-powered scope that isn't referenced to anything.  So if you want to measure the voltage drop across a mosfet, you don't have to worry about where ground is, or blowing anything up.  But probably because of the small capture memory, I believe triggering only works at 20ms and faster.

In the video, I think Dave has the 138 on Auto mode, and I think it wouldn't wander if it was in Normal mode.

And for the adventurous, there's a two-channel version (the Wave 2) for $65 plus a battery.  Does X/Y, has a function generator, etc., but basically the same specs.

I'm impressed they can do it with the same stm32f103
Design documents here: https://jyetech.com/dso-150-shell-oscilloscope/

[tszaboo]

Oh, when a kit of ear tells you in chinglish that "do not support thief" and "report copies".
That is a bit ironic, isn't it.

[monz]

On the Tektroninics 2213A focus problem, this is a common issue with these. There are a number of 510k resistors in the focus/high voltage circuit that drift in value. Check them out of circuit, you’ll likely find they’re no where near 510k, replace them all, there are 6 or so. There are dangerous voltages present, so obviously be careful. I too bought one on eBay a long time ago knowing it had a focus issue and therefore cheap hoping it would be easy to fix and it was.

It’s actually covered here:

https://www.eevblog.com/forum/repair/tektronix-2213a-repair/

[T3sl4co1l]

Heh, that PDI DM-950BT meter with the ATMEGA in it, willing to bet that's quite hackable. Looks like it's got a programming header right beside it!

Tim

[Fryguy]

I just watched #1272 Mailbag and noticed that Dave likes the fuses at 38:11 . . . these are old 25V/47µ Roederstein Caps 
And the Hybrid-Resistor-Module-Things at 39:40 are labeled "Thermal Fuse" on the PCB . Very interesting pieces - worth a closer look .