Repairing a Marconi Instruments 2955A Radio Communications Test Set, part 1

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Mikko has written an article about Marconi 2955A repair:

First off, I decided to see what was the deal with the CRT. I have never worked on CRTs before, I have understanding of how the picture is formed by steering the electron beam using the deflection coils but that’s about it. I know a charged CRT can be deadly so I took my own safety very seriously. After carefully removing and inspecting the CRT drive board AC1, I noticed that someone had been there before. There were telltale signs everywhere. Screws missing, protective plastics missing, horrible soldering jobs… The CRT-to-chassis grounding strap appeared to be on but when I touched it ever so slightly, it just came off. I also noticed a TO-220 transistor (vertical deflection control) had apparently been changed by cutting off the leads from the old one and badly soldering a replacement on.

More details at Mikko’s blog.

Spectrum analysis with RFM12B

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Martin Harizanov writes, “The comments to my last blog post got me thinking if I had chosen the right RFM channel at home, obviously if the channel is noisy that directly affects reception and increases the error rates. I use the default 868Mhz setting for the RFM12B/RFM69s at home and decided to check if the channel is clear from other transmissions. I remembered seeing a RFM12B spectrum analyzer project over at Jeelab some years ago, and 5 minutes later was running the spectrum analyzer using one of my Funky v3s equipped with a 868Mhz RFM12B.”

More details at Martin’s blog.

PCB inspection stand for Chinese magnifier

Chinese Magnifier

Tom Keddie writes, “On the last hacker camp I picked up a magnifier with HDMI output on Taobao (or more expensive but no airfare needed 14MP HDMI HD Microscope USB Industrial Camera 180X C mount Lens Stereo Stand)
I find myself needing to peer into and under packages a lot, I got sick of holding the pcb and trying to focus so I laser cut this little stand. It has two angles on it for different views. I find it is especially useful for USB connectors.”

Source files are at Github.

Via the forum.

 

App note: Combining GDTs and MOVs for surge protection of AC power lines

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Another circuit protection from power surges/spikes application note from Littelfuse. Link here (PDF)

AC power line disturbances are the cause of many equipment failures. The damage can be as elusive as occasional data crashes or as dramatic as the destruction of a power supply, computer terminal, or television set. Power line disturbances go by many names transients, surges, spikes, glitches, etc. but regardless of the name, an understanding of their characteristics and the operation of the various protection devices available is necessary to design an effective protection circuit. This Application Note will illustrate how to design high performance, cost-effective surge protection for equipment connected to AC power lines. The role of gas discharge tube (GDT) surge arresters specifically designed for AC power line protection will also be discussed.

Free PCB Sunday: Pick your PCB

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We go through a lot of prototype PCBs, and end up with lots of extras that we’ll never use. Every Sunday we give away a few PCBs from one of our past or future projects, or a related prototype. Our PCBs are made through Seeed Studio’s Fusion board service. This week two random commenters will get a coupon code for the free PCB drawer tomorrow morning. Pick your own PCB. You get unlimited free PCBs now – finish one and we’ll send you another! Don’t forget there’s free PCBs three times every week:

Continue reading “Free PCB Sunday: Pick your PCB”

App note: Circuit protection for Lithium-Ion and lithium polymer rechargeable battery applications

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Adding secondary circuit protection to ensure safety when using Lithium-Ion and Lithium polymer batteries discussed in this app note from Littelfuse. Link here (PDF)

The introduction of portable devices with advanced features and the demand for longer run times and has resulted in innovations in the battery technologies used for portable applications. The latest generation of battery technologies has met these needs by increasing the energy density of the battery cell. The increase in energy density allows low voltage applications such as mobile phones to operate off of a single cell, and multiple cell applications to achieve longer operating times. The energy density change has also required that protection circuits be included with all rechargeable Lithium-Ion and Lithium Polymer battery packs. Protection circuits in packs include a control IC, MOSFET switch, external capacitor for IC timing to prevent inadvertent MOSFET operation, capacitors or varistors to protect against ESD and system transients, and secondary protection devices. The control IC and MOSFET provide primary protection for the pack during both charge and discharge cycles. This protection circuitry is offered in a single package solution for battery pack protection. While the primary protection circuit is reliable, to ensure complete user safety secondary protection devices are included to protect in situations outside of the normal range of operation. The secondary protection is provided by the use of overcurrent protection devices.

Free PCB coupon via Facebook to 2 random commenters

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Every Friday we give away some extra PCBs via Facebook. This post was announced on Facebook, and on Monday we’ll send coupon codes to two random commenters. The coupon code usually go to Facebook ‘Other’ Messages Folder . More PCBs via Twitter on Tuesday and the blog every Sunday. Don’t forget there’s free PCBs three times every week:

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Breaking a Teensy U2F implementation: why you shouldn’t write your own crypto

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Aidan (a.k.a. makomk) writes:

A while ago, Google created a two-factor authentication scheme called U2F. The general idea is as follows. You have a little USB dongle that you can register with sites. When you enable U2F on a site, the dongle gives that site a public key and a key handle, and that dongle is the only device that can use that key handle to sign things with the corresponding public key. So from then on, websites can hand over the key handle and a challenge, and if they get back a valid signature they know that whoever’s logging in has the dongle you used to sign up.

More details at The Lair of Mako site.

A development board for the STM32F042 TSSOP package

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Andy Brown designed a development board for the STM32F042 in the TSSOP20 package:

Development board features

  • USB. The 042 series supports USB and although 32Kb is not a lot of space to include a USB driver and your application logic it does make sense to hook up those USB data lines and thereby enable USB device development.
  • Switching regulator. All the development boards that I’ve seen seem to use a low dropout regulator (LDO) to supply power to the MCU which means that they’re unable to supply much current to any peripherals that you’re prototyping. The discovery boards warn you not to draw more than 100mA and many of the 3rd party boards use one of the 1117 regulators which, with up to a 1A limit, look great on paper but the universally chosen SOT-223 package will burn up in smoke long before you get anywhere near that figure.
  • VDDA control.The discovery boards allow you to supply VDDA externally if required. I’d like to keep this ability.
  • Onboard 8MHz crystal. All the F0 series can be clocked from the internal high speed internal (HSI) 8MHz oscillator with an option to use an external 8Mhz crystal. I’ll include such a crystal on my board.
  • Onboard NPN transistor. I often need to use an NPN transistor as a low-side switch to control a load either requires too much current to power from a GPIO or is running from a different voltage level (e.g. 5V). I’ll include a simple transistor on this board configured ready to function as a switch.
  • A LED. Because, well, you know, blinky.

Project info at Andy Brown’s blog.

Check out the video after the break.

Continue reading “A development board for the STM32F042 TSSOP package”

Search Github projects by component, find design references

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Search Github hardware by component to find examples and references for your next project. Big schematic and PCB previews mean quick and easy browsing without opening a CAD program.

TomKeddie first mentioned this idea at Hacker Camp Shenzhen, and later in the forum and on WeChat. Tom generously shared his scraping/search method. Eagle 6+ files are XML, so we can find them on Github by searching for the “eagle SYSTEM” tag in files with “extension:sch”. That gives more than the maximum 100 pages of results, so we filter by file size and increment size 500 bytes at a time “size:1001…1500”. We use the normal user search interface, parse the HTML results, and grab all urls ending with .sch. While Github has an API, that API doesn’t give access to search code search without specifying a repository by name (probably so people don’t do what we did…).

There are a number of limitations. Only Eagle projects are indexed, a search for KiCad files inspired little interest in expanding. Before Eagle 6.0 files were not XML and will not be included. Github search only indexes code files up to ~390K, larger files will not be included. If Github improves access via the API we will expand the index.

Scraping all of the files over terrible Chinese internet took about a week. Searches were performed at minimum 32 seconds apart. Some files were incomplete (lacked closing tag). Some files have extra ‘>>’, usually a merge error tag. Some files were just corrupt. These all caused Eagle to hang until the window was manually closed. Working with Eagle from the command line has been most unpleasant.

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Via the forum.

 

 

RFM69_ATC: Automatic Transmission Control

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Felix of LowPowerLab writes:

There is now a new extension to the RFM69 library. It’s called RFM69_ATC aka Automatic Transmission Control. Many thanks to Tom Studwell who implemented this and shared it in the forum. The basic idea behind this extension is to allow your nodes to dial down transmission power based on the received signal strength indicator (RSSI). For instance a sleepy battery node like a MotionMote sits still inside the home and usually has a very strong received signal, somewhere in the range of -30 to -40dBm when transmitting at full power. You could manually tune that down using radio.setPowerLevel(..) in code but its tedious and is a static change, if you move the node or conditions change it will not be smart to adjust the power level to the new environment. However with RFM69_ATC this is done automatically for you, you just need to indicate a target RSSI. On each packet sent and ACK received (using sendWithRetry(…) is required), the node analyzes the actual RSSI and continuously adjusts its own transmission power level of the RFM69 transceiver to attempt to match the target RSSI (+ or -).

More details at LowPowerLab blog.

Analog Devices AD587KN 10V reference

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SteelCity Electronics published an article about Analog Devices AD587KN 10V reference:

I recently got hold of an Analog Devices AD587KN high precision 10.000V reference chip.
This model of chip has an output value of 10.000V ± 5mV (that is, an output value of 9.995V to 10.005V) straight out of the factory. A voltage drift of 10ppm/°C at 25°C meaning that the output voltage will drift by 10μV for each 1°C the chip is exposed to. Additionally, the chip has a voltage trim input, so if you have access to a precision voltmeter, the chip’s output value can be adjusted even closer to 10.000V.
Alternatively, the chip’s output can be trimmed to a value of 10.24V. You may think that a value of 10.24V seems like a strangely familiar number. A value of 1024 is the decimal representation of 10bits, that is 2∧10 = 1024. Why would I want a voltage reference that outputs a value of 10.24V? Because it makes any ADC or DAC conversions much simpler.

Details at SteelCity Electronics site.

#FreePCB via Twitter to 2 random RTs

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Every Tuesday we give away two coupons for the free PCB drawer via Twitter. This post was announced on Twitter, and in 24 hours we’ll send coupon codes to two random retweeters. Don’t forget there’s free PCBs three times a every week:

  • Hate Twitter and Facebook? Free PCB Sunday is the classic PCB giveaway. Catch it every Sunday, right here on the blog
  • Tweet-a-PCB Tuesday. Follow us and get boards in 144 characters or less
  • Facebook PCB Friday. Free PCBs will be your friend for the weekend

Some stuff:

  • Yes, we’ll mail it anywhere in the world!
  • Check out how we mail PCBs worldwide video.
  • We’ll contact you via Twitter with a coupon code for the PCB drawer.
  • Limit one PCB per address per month please.
  • Like everything else on this site, PCBs are offered without warranty.

We try to stagger free PCB posts so every time zone has a chance to participate, but the best way to see it first is to subscribe to the RSS feed, follow us on Twitter, or like us on Facebook.

Repairing the TUNE capacitor on the Heathkit HL2200 (SB-220) amplifier

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KA7OEI  did a repair on his amplifier.  He documented the whole process on his blog:

Earlier this year I picked up a Heathkit HL2200 amplifier (the newer, “brown” version of the SB-220) at a local swap meet for a reasonable price.  What made it particularly attractive was that it not only had a pair of new, graphic 3-500Z tubes in (Chinese-made, but RF-Parts Inc. tested/branded) but it also had a Peter Dahl “Hypersil” tm power transformer rather than the “just-adequate” original Heathkit transformer and an already-installed low-voltage keying circuit which meant that rather than nearly 100 volts on the keying line to operate relays there was only a few milliamps at a few volts.

More details at KA7OEI’s blog.

Teardown & analysis of a Keysight InfiniMax III N2802A 25GHz active probe

A teardown & analysis of a Keysight InfiniMax III N2802A 25GHz active probe from TheSignal Path:

In this episode Shahriar takes a close look at one of Keysight (Agilent) InfiniMax III active probes. The model N2802A offers 25GHz of analog bandwidth, 17.5pS of rise time and a total differential input capacitance of 32fF at 10k-Ohm input impedance. The front-end amplifier of this active probe is designed in an in-house InP process, the same process responsible for the front-end of the X-Series Keysight oscilloscopes.
The teardown of the probe shows the control circuitry in the main probe body built around a PIC 16F877 microcontroller coupled to a DAC, EEPROM memory and various high-current and precision op-amps for biasing. The main front-end microwave module reveals the InP ASIC and supporting microwave circuity. There seems to be a dual-path design to provide a large DC common-mode offset capability as well as a high-bandwidth.

 

Dynamic microphone preamplifier

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Dilshan Jayakody published a new build, a microphone preamplifier:

This is single chip dynamic microphone preamplifier which is design to drive using commonly available 12V single rail power supplies. Preamplifier in this article is build around popular NE5532 dual low noise operational amplifier IC and this preamplifier is specifically constructed to drive professional 600Ω dynamic microphones.
This preamplifier consists with two amplifier stages and initial amplifier is design to get 36dB gain and final preamplifier is used to get 16dB of gain. Preamplifier gain controller is placed in between those two amplifiers and this separation allows reducing clipping in output waveform.

Project info at  Jayakody’s blog and  Elect.wikispaces.com.

App note: Transient suppression devices and principles

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App note from Littlefuse on how do transient suppression devices protect electronic circuits. Link here (PDF)

There are two major categories of transient suppressors: a) those that attenuate transients, thus preventing their propagation into the sensitive circuit; and b) those that divert transients away from sensitive loads and so limit the residual voltages.

Attenuating a transient, that is, keeping it from propagating away from its source or keeping it from impinging on a sensitive loadis accomplished with filters inserted in series within a circuit. The filter, generally of the low-pass type, attenuates the transient (highfrequency) and allows the signal or power flow (low-frequency) to continue undisturbed.

Diverting a transient can be accomplished with a voltage-clamping type device or with a “crowbar” type device. The designs of these two types, as well as their operation and application, are different enough to warrant a brief discussion of each in general terms.

Free PCB Sunday: Pick your PCB

IRToy

We go through a lot of prototype PCBs, and end up with lots of extras that we’ll never use. Every Sunday we give away a few PCBs from one of our past or future projects, or a related prototype. Our PCBs are made through Seeed Studio’s Fusion board service. This week two random commenters will get a coupon code for the free PCB drawer tomorrow morning. Pick your own PCB. You get unlimited free PCBs now – finish one and we’ll send you another! Don’t forget there’s free PCBs three times every week:

Continue reading “Free PCB Sunday: Pick your PCB”

App note: An overview of electromagnetic and lightning induced voltage transients

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Application note from Littelfuse on sources of transient voltages that can induced in electronic circuits. Link here (PDF)

This Note is an overview of the sources and nature of various transient overvoltages, and the problems that may result.
Transients in electrical circuits result from the sudden release of previously stored energy. This energy can be stored within the circuit and released by a voluntary or controlled switching action or it can be outside the circuit and injected or coupled into the circuit of interest.

Transients may occur either in repeatable fashion or as random impulses. Repeatable transients, such as commutation voltage spikes, inductive load switching, etc., are more easily observed, defined and suppressed. Random transients occur at unpredictable times, at remote locations, and may require installation of monitoring instruments to detect their occurrence. Experience has been accumulated to provide reasonable guidelines of the transient environments in low voltage AC power circuits, telecommunications equipment and automotive electrical systems.

Effective transient overvoltage protection from a clamping device requires that the impulse energy be dissipated in the suppressor and the voltage held low enough to ensure the survival of circuit components. The following sections will discuss in detail the two categories of transients, how they occur, their effects and their detection.

App note: AN-42 IC provides on-card regulation for logic circuits

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This application note (PDF!) from TI provides on-card regulation for logic circuits:

Because of the relatively high current requirements of digital systems, there are a number of problems associated with using one centrally-located regulator. Heavy power busses must be used to distribute the regulated voltage. With low voltages and currents of many amperes, voltage drops in connectors and conductors can cause an appreciable percentage change in the voltage delivered to the load. This is aggravated further with TTL logic, as it draws transient currents many times the steady-state current when it switches.
These problems have created a considerable interest in on-card regulation, that is, to provide local regulation for the subsystems of the computer. Rough preregulation can be used, and the power distributed without excessive concern for line drops
The local regulators then smooth out the voltage variations due to line drops and absorb transients.