Automated channel switching with Motorola GM3x0

Automated channel switching with Motorola GM3x0

With the integration of POCSAG/DAPNET features into the MMDVM/MMDVMHost I came to think about if it would be possible to combine an MMDVM repeater/HotSpot with a DAPNET tranmitter. The advantage in Germany is that there is a single coordinated frequency for POCSAG tranmissions on UHF. 439.9875MHz is used for fixed-frequency pagers which are modified to receive on that frequency. With latest hand-programmable pagers (e.g. AlphaPoc) it would basically be possible to set them to the repeater frequency but that wouldn’t work while one is en route.
In the programming software for Motorola GM3x0 radios I found an interesting GPIO setting called “Channel Steering”. Some line of the help function revealed that it would exactly do what I expected. You can trigger a GPIO and the radio switches channels.

Via Notizbl0g.

Check out the video after the break.

Shenzhen to Hong Kong on High Speed Rail

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Even though Shenzhen and Hong Kong are basically the same city on opposite sides of a border, it’s still a frustratingly long trip to Hong Kong Central for a Reuben at Morty’s Deli. The new high speed rail line linking downtown Shenzhen to downtown Hong Kong makes the trip in just 15 minutes. A lot of frequent travelers are hoping it just got a lot easier to eat delicious pastrami on a whim, but with all the formalities of Chinese rail will it really cut the travel time? We jumped on to find out!

futian-station-2

Futian Railway Station is two metro stops from the Huaqiangbei electronics market, in the Futian Central Business District. It’s always empty, despite being several years old and absolutely massive. Unlike most Chinese rail stations, it’s actually in the middle of the city.

futian-tickets

It usually takes less than 10 minutes to collect tickets and go through the security checks. Shenzhen North station is on the same high speed rail line, but it’s so busy that it often takes more than an hour to get into the station. Foreigners can’t use the ticket vending machines, so we had to go to the window and hand over our passports to buy tickets from a human.

futian-security

Security checks make Chinese high speed rail more like flying out of an airport. Identity check, baggage x-ray, metal detector, and finally a manual pat-down. This is where Futian station really shines – it’s so empty that security takes less than a minute. Security in Shenzhen North can take 30 minutes or more.

boarding

Everyone riding the train was super excited. It was the same atmosphere as when the A380 was a new and exciting airplane to ride. Lots of pictures and selfies.

cover

This train has the Hong Kong MTR logo on the side, and seems to serve only Futian and Kong Kong stations. There were no other passengers on the train from stations further north when we boarded.

business-cabin

Second class tickets are around $9, first class is around $15. About the same price as taking the metro.

This is the first class cabin. Some trains also have a tourist class or business class with lay-flat seats, but at $50 it seems a bit too posh for a 15 minute train ride.

speed-display

Maximum speed was around 180 km/h. The entire trip is in an underground tunnel so there’s not much to see. The WIFI didn’t seem to work, but there was 4G mobile data during the whole ride.

border

In Hong Kong there’s a joint border crossing for both Hong Kong and China. After getting off the train you go through immigration to leave China, walk a bit, then show your passport to get into Hong Kong. Chinese immigration does a customs check on the way out, every bag of any size has to go through an x-ray machine.

kowloon-west-station

Kowloon West Station is magnificent, but also a bit of a chaotic mess. It’s also not really anywhere useful, it’s a ten minute walk through malls to find a metro to Hong Kong Central.

kowloon-west-ticket-windows

Returning to Shenzhen is much less convenient. The line to purchase tickets is super long, like the line for the Hong Kong Airport McDonald’s. The line to pickup tickets purchased via apps is more reasonable, like the line for the Hong Kong Airport Popeye’s. As in China, foreigners can’t buy tickets at the vending machines. After seeing this mess we decided it would be faster and more pleasant to catch the metro back instead.

Takeaways

From our door to Morty’s Deli in Central usually takes about 1 hour and 45 minutes using a cross border bus or the metro. It took about 1 hour and 15 minutes using high speed rail. A half hour faster isn’t bad, but it also takes a lot of planning. Tickets need to be purchased in advance, timing at the station needs to be just right, and West Kowloon isn’t exactly a useful location in Hong Kong.

Coming back to Shenzhen from Hong Kong seems like it could take even longer than a bus or metro. There’s huge crowds picking up tickets for destinations all over mainland China, so ticket collection takes forever. That means arriving early to get the tickets, then extra waiting around for a scheduled train. It’s so much easier to step onto the next metro back to Shenzhen and enjoy the ride.

Even if high speed rail is consistently faster, the experience of doing it requires all the focus and planning of catching a flight at an airport. We’ll take it from Shenzhen Futian to Hong Kong in the future, but with so much planning involved it’s always going to be easier to take the metro back.

ESP32 AM radio transmitter

am-modulation

A how-to on making a simple AM radio transmitter using the ESP32 microcontroller by Bitluni:

AM Radio transmissions are based on a carrier signal which is modulated by the audio signal. It’s a very basic principle but prone to noise from the environment. Using the ESP32 it is really simple to generate an analog signal using the built-in DACs. With the provided code here just a wire as an antenna has to be connected to the pin 25 of the ESP32. The transmission will end up on the AM frequency ~835kHz.

Via Bitluni’s Lab.

Check out the video after the break.

Project PITA: Build a mini mass deauther using Bettercap and a Raspberry Pi Zero W

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evilsocket shared a how-to on making a mini WiFi deauthenticator using Bettercap and a Raspberry Pi Zero W:

A few days ago I started playing with some idea I had from a few weeks already, using a Raspberry Pi Zero W to make a mini WiFi deauthenticator: something in my pocket that periodically jumps on all the channels in the WiFi spectrum, collects information about the nearby access points and their connected clients and then sends a deauthentication packet to each one of them, resulting in some sort of WiFi jammer on the 802.11 level. As an interesting “side effect” of this jammer (the initial intent was purely for the lulz) is that the more it deauths, the higher the changes to also sniff WPA2 handshakes.

See the full post on Evilsocket blog.

Inside a two-quadrant power supply – Agilent 66312A teardown and experiment

Agilent66312A

Kerry Wong did a teardown of an Agilent 66312A dynamic measurement DC source:

Typically, a lab power supply can only operate within a single quadrant. Take a positive voltage power supply for example, it can only output or source current. If any attempt is made trying to sink current into the power supply by connecting a voltage source with a higher voltage than the output voltage of the power supply, the power supply would lose regulation since it cannot sink any current and thus is unable to bring down and regulate the voltage at its output terminals.
The Agilent 66312A dynamic measurement DC source however is a two-quadrant power supply, it not only can source up to 2A of current between 0 and 20V, but also can sink up to 1.2A or 60% of its rated output current as well. Although lacking some key functionality of a source measure unit (SMU), Agilent 66312A can nevertheless be used in similar situations where both current sourcing and sinking capabilities are needed.

More details on Kerry Wong’s blog.

Check out the video after the break.

App note: Minimizing light flicker in LED lighting applications

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Another application notes from Richtek this time on LED lamps flickering. Link here

Applying LEDs in offline retrofit lamps seems straightforward, but should be done with care to achieve similar light quality as the conventional lamp that the user is trying to replace. Light flicker is one of the aspects that need to be considered carefully during LED lamp design to avoid customer complaints from the field. This application note explains the LED lamp flicker phenomena in relation to driver topology and LED characteristics, and provides solutions based on several Richtek LED drivers in combination with specific LED strings. A practical flicker measurement method is explained as well, that can be used to measure light flicker in LED lamps.

App note: Li-ion battery and gauge introduction

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Richtek app note for Li-ion battery definitions and gauge introduction. Link here

SOC is defined as the status of available energy in the battery and usually expressed as percentages. Because the available energy change depends on different charging/discharging currents, temperatures and aging effects, the SOC could be defined more clearly as ASOC (Absolute State-Of-Charge) and RSOC (Relative State-Of-Charge). Typically, the range of RSOC is from 0% to 100%, a fully charged battery’s RSOC is always 100% and a fully discharged battery has 0% RSOC. The ASOC is a reference calculated by Design Capacity which is a fixed capacity from when the battery is manufactured. A fully charged new battery will have 100% ASOC, but a fully charged aging battery could be less than 100% because of different charge/discharge conditions.

Battery management is part of power measurement. The fuel gauge is responsible to estimate the capacity of battery in the domain of battery management. The basic function of fuel gauge is to monitor the voltage, charge/discharge current and battery temperature, and to estimate the battery’s SOC and Full Charge Capacity (FCC) of battery. There are two classic methods to do the SOC estimation which are Open Circuit Voltage (OCV) and Coulomb Counter, respectively. The other method is dynamic voltage-based algorithm designed by RICHTEK.

Pocket high voltage generator quick build

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Aki made this DIY pocket HV generator:

There are times you find yourself looking for a relatively high voltage (100V to 200V often in my case) but low current DC power supply. I have zener diodes that are higher than 30V, which makes the lab supply useless, and filament LEDs with forward voltage over 60V. When I need to test them quickly, I used to hook up a simple rectifier circuit to a variable AC power supply (nothing more than a slidac with isolation transformer). While this gets job done, the setup is capable of supplying much too high current (1A or more), so I was always very nervous and extra careful in handling the circuit. All I need is a little HV generator that gives me around 200V DC and only capable of supplying a milliamp or less. Realizing that I do have such design available – one of the Nixie supply circuit – I just decided to put one together to use.

Project info on The LED Artist blog.

Two bits per transistor: high-density ROM in Intel’s 8087 floating point chip

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Ken Shirriff has a great write-up about the multi-level ROM in Intel’s 8087 floating point chip:

The 8087 chip provided fast floating point arithmetic for the original IBM PC and became part of the x86 architecture used today. One unusual feature of the 8087 is it contained a multi-level ROM (Read-Only Memory) that stored two bits per transistor, twice as dense as a normal ROM. Instead of storing binary data, each cell in the 8087’s ROM stored one of four different values, which were then decoded into two bits. Because the 8087 required a large ROM for microcode1 and the chip was pushing the limits of how many transistors could fit on a chip, Intel used this special technique to make the ROM fit. In this article, I explain how Intel implemented this multi-level ROM.

More details on Ken Shirriff’s blog.

DIRTY CABLES: a new cable editor

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DirtyCables.com has a live preview of a new custom cable builder. This is a from-scratch rewrite of the editor at DirtyPCBs with new features based on your requests:

  • Isometric connector drawings with pin numbers save a trip to the datasheet
  • Improved connector selector with room for additional info
  • One to many “Y” connections. Same connector “U” connections
  • Bigger, cleaner interface

Check out the live demo, and read about the updates below. The new editor is in preview mode, saving and buying cables is disabled.

add-hover

The editor is full screen and adjusts somewhat to different device sizes. Click “Add Connector” or “Add Wire” to insert a new part.

cables-add-CH

The add part dialog has been completely reworked. Choose the connector family to see a photo and isometric drawings with pin numbers. There’s room to add more information about the part in the future.

cables-complex

Click and drag to connect a wire and a connector. This is different than the click-to-select interface in the previous editor, and lacks the UI bugs. Pins, labels, and connections are handled by an open source library called jsPlumb.

Y-type one-to-many connections can be made for some parts. It’s also possible to do U-type connections that connect two pins of the same connector to the opposite ends of a single wire.

flip

Click to flip the connector and pin order. The reverse view shows the bottom side isometric drawing.

length

Click the wire to edit the length. Click “X” to remove the wire and its connections. This is much more compact than the old editor and makes complicated cables look a lot cleaner.

cables-docs

DirtyCables.com will be the new dedicated  site for the Dirty Cables service. The new site has simple and clear navigation, and it gives us room to grow the cable documentation and resources. In the next year we hope to double the connector and wire options, and add 100 common pre-made cables to the store. Of course it would also be nice to have mating sockets for all the connectors.

It’s a big decision to move this service outside DirtyPCBs, but we’ve made a lot of progress in the last year. We have a solid supply chain, we can accurately estimate prices, and we have a procedure to evaluate cable samples before they ship. DirtyCables is currently in preview mode, but it should be open for orders early next week.

Try out the new cable editor preview here. Can’t wait to buy custom cables? DirtyPCBs’ cable creator is ready to take your order. Need to see the connectors? Try our cheap Dirty Connector Sample Kits.