EEVblog #1272 - Mailbag - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: December 18, 2019, 07:31:08 am
content: More Mailbag!Subscribe to Dave on LBRY:https://lbry.tv/@eevblog:7SPOILERS:Vintage Tek Scopes2:57 8 Cent Touch Sensor Chip TTP223 from TonTek:https://lcsc.com/products/Touch-Screen-Controller-ICs_902.html?q=ttp2239:08 DefPom's new open source BOM tool MyPartsBin:https://mypartsbin.com/https://www.youtube.com/user/TheDefpomCasio FX-730P Calculator11:49 FREE Multimeters went to a good cause, and Amazon Returns14:07 CB2 Micro Kit:http://cb2.qrp.gr/17:02 50,000 Count $150 CEM DT-9969 / PDI DM-950BThttps://pdimeters.com/products/Electronic-and-General-Purpose/DM950BT.phpThe Church Of Tesla:https://www.churchoftesla.org/31:34 Vintage Telecom telephone gear, and mechanical counters.41:39 PCB piezotronics RS Technologies Torque sensing wrench46:58 Big Arse Variable Resistor48:27 JYE Tech DSO138 Oscilloscope Kit

author: Flappy
author_rank: Contributor
timestamp: December 18, 2019, 08:55:08 am
content: 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.

author: Flappy
author_rank: Contributor
timestamp: December 18, 2019, 09:01:31 am
content: 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.

author: Flappy
author_rank: Contributor
timestamp: December 18, 2019, 09:16:54 am
content: 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.

author: Flappy
author_rank: Contributor
timestamp: December 18, 2019, 09:28:55 am
content: 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.

author: Flappy
author_rank: Contributor
timestamp: December 18, 2019, 09:33:52 am
content: 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.

author: johnlsenchak
author_rank: Frequent Contributor
timestamp: December 18, 2019, 05:58:29 pm
content: 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 telephoneanalog PBX systemsthat are not used anymore due to VOIP technology

author: Peabody
author_rank: Super Contributor
timestamp: December 18, 2019, 07:32:36 pm
content: 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.

author: johnh
author_rank: Regular Contributor
timestamp: December 19, 2019, 07:18:09 am
content: 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.

author: thm_w
author_rank: Super Contributor
timestamp: December 19, 2019, 10:02:34 pm
content: Quote from: Peabody on December 18, 2019, 07:32:36 pmI'm impressed they can do it with the same stm32f103Design documents here:https://jyetech.com/dso-150-shell-oscilloscope/

author: tszaboo
author_rank: Super Contributor
timestamp: December 19, 2019, 10:33:30 pm
content: 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.

author: monz
author_rank: Contributor
timestamp: December 20, 2019, 02:51:31 am
content: 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/

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 21, 2019, 09:21:25 am
content: 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

author: Fryguy
author_rank: Regular Contributor
timestamp: January 27, 2020, 09:35:30 pm
content: I just watched #1272 Mailbag and noticed that Dave likes the fuses at 38:11 . . . these are old 25V/47µ Roederstein CapsAnd the Hybrid-Resistor-Module-Things at 39:40 are labeled "Thermal Fuse" on the PCB . Very interesting pieces - worth a closer look .