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1  Mobile Linux Devices / Other Android Mobile Phones and Tablets / Hacking the Clover POS tablet
 on: Jan 23rd, 2023, 7:25pm 
Started by Administrator | Post by Administrator
Hacking the Original Clover Station POS (C100) tablet.
The Original Clover Station has been considered "End of Life" by Clover Network Inc., and replaced by a number of different hardware POS devices.
Since the Original  Clover Station POS (C100) is no longer supported by Clover, these devices are now found in quantity on the surplus market.
The basic clover hardware is actually pretty nice -- especially for when it was released in 2014.  It consists of a good quality 11.6", 1366x768 Touch Screen Display driven by a NVidia Tegra 3 SOC.  It features 1G of RAM (Which was sufficient for the versions of Android that existed at the time), and 8G of flash.  It runs a customized version of Android 4.2.2.

So can these be converted into a regular tablet, or repurposed for other uses?
Before getting much further into this, I will say that we are dealing with proprietary hardware and software here.
I will also say that I got mine (Tablet only) for $10, and I only got it yesterday.  This will be updated as I learn more.
Much of the Clover Station functionality is actually in the printer.  The printer connects to the "Tablet" (The Clover Touchscreen Display) via a proprietary cable.  The power supply, and breakout to standard ports in all done inside the printer.  The printer is powered by a 24V, 5A Power brick.  In addition to the power jack, and the proprietary interconnect port, the printer also contains 4 standard USB ports, and Ethernet port, and an RJ12 connector that is intended for an optional cash drawer or other accessories.  This may be some sort of serial port.
So in functionality, the Printer contains something similar to a USB travel hub with Ethernet.
The proprietary cable that connects to the Tablet contains the following as far as I can tell:
  • Unregulated Power to the Tablet
  • Two (2) Partial USB ports
  • Ground

More specifically, here is the Pinout of the 12 Pin connector inside the tablet:
Pin 1 is at the bottom in the following picture (near the circle).
1.   +Power
2.   +Power
3.   No Connection (No contact on the Motherboard connector)
4.   USB 1 Data  -
5.   USB 1 Data  +
6.   Ground
7.   USB 2 Data -
8.   USB 2 Data +
9.   Unknown Black Wire (no continuity to ground)
10. Ground
11. Ground
12. Ground
  • All grounds seem to be the same, and the same as chassis/shielding ground.  I have not found any separate ground.
  • The Power supplied to the Display Tablet section seems to be an unregulated or higher voltage.

A Little More About the Power:
I am not sure if it directly fed from the +24V power brick.  All I can say is that it must be enough to run the 5 VDC Buck converter (Red Square shown in the picture).  Mine starts up at about 6.7 VDC.  At this supply voltage, the tablet section draws about 800mA.
For testing, I soldered a short length of wire to positive side of the filter capacitor that is right next to the interface connector. This prevents damage to the connector.
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2  Original Projects and Builds / Other Builds and Projects / Re: 7591 Amp Build (from Rowe/AMI R-4359)
 on: Dec 26th, 2022, 3:40pm 
Started by Administrator | Post by Administrator
For now, I am considering this project essentially complete.
Here are the official "Glamor Shots" of this project:

It generally sounds great and has plenty of horsepower and bass. It also has the clear, crisp highs one would expect from a tube amp.
I still may do some more work on the Driver/PI circuit in the future if I learn more.
I also may still do some chassis modifications, including:
  •  2 holes just under the Spectrum display for access to the clock/mode set buttons. Right now you basically can't set the clock, but I don't think the clock display is important.
  •  I may install a toggle switch to the right of the display to allow the Spectrum analyzer to be turned off.
  •  I need to install some reflective tape inside the HV enclosure to keep the Green LED light from leaking through the paint at the front.
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3  Original Projects and Builds / Other Builds and Projects / Re: Poor Man's version of the Monster GO DJ
 on: Dec 4th, 2022, 8:24am 
Started by Administrator | Post by Administrator
I DJ'ed for a 5 hour gig yesterday (Saturday).  The Poor Man's GO DJ worked almost perfectly for the whole gig, and using the new digital voltmeter, I could tell that the batteries were actually charging throughout the day.  This was the first time I was confident that power would not be an issue.
I should also mention that I was using a normal, unmodified USB mini cable, although it was a qood quality one.
I did have a problem with several MP3 files ending abruptly, but this is not the fault of the player.  There is a known issue with lame that causes wrong header information to be written to Variable Bit Rate (VBR) MP3 files, so if I miss running ripped music through vbrfix, this issue can result.  FLAC files are not effected.
Other than that, the day was pretty much flawless.  Nice weather, lots of very nice cars, and -- Food Trucks !!, One of which donated a fried shrimp meal to me.
The real GO DJ?  It stayed in the truck.
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4  Original Projects and Builds / Other Builds and Projects / Re: Poor Man's version of the Monster GO DJ
 on: Nov 30th, 2022, 2:22pm 
Started by Administrator | Post by Administrator
I am basically applying the Infinite Monkeys Theroem to power supply design.
I agree that providing +/9 Volts and + 5 Volts from a Lithium Ion battery source is not complex these days;  However, I have a few constraints:
1.  I am not using a microprocessor to do the battery management, as is done in most devices such as the Real Monster GO DJ, a mobile phone,  or this tablet I am using right now.
2.  I am not making custom PC boards, or purchasing individual components.  I am limited to available modules/circuit boards.
3. The high power requirements of the 2 player modules.
I have basically returned to the original design with the following changes:
1.  I am using the 2A battery management board instead of the original Portable Battery Pack board.
2.  I am using a Digital Panel Meter (DPM) for battery monitoring instead of a 0-100% meter, or the LED's on the battery management board.
3.  I have added a small heat sink to the same adjustable boost module that I was using before.
Here is a current schematic of the Poor Man's GO DJ power system:

Note that +5 VDC for the DPM is provided by the Battery Management Board.  This allows me to check the battery voltage while the rest of the unit is fully off -- In other words, I can check both the no-load voltage and the loaded voltage of the battery pack.  I can also monitor the voltage during charging with the unit off.
Another big improvement was basically to make a low-resistance USB A - to - micro charge cable.  I cut a 10' cable, which used slightly heavier guage wire, down to about 4 ft.  With this cable, the PM GO DJ will now charge at 1.2A (up from 900mA using a regular USB cable.)
This arrangement seems to work adequately.  I have run the PM GO DJ for several hours without drain on the batteries.  The boost board still gets warm, but the heat sink is definitely helping.
Why not run the +/-9 VDC Boost either directly from the Battery Management board, or from the battery -- thus reducing load on the 5V board?  As mentioned in a previous post, when the Battery Management board is simultaneously charging and supplying power, the output drops below 4.75VDC, but it also seems unstable.  To prevent any noise, I did not want to chance running anything from this output.  Also, the +/-9 VDC Boost will not function when the input drops much below 5V.
Remaining problems -- There is still no real under volt protection.  If the unit is left on, the boost converter will stall someplace around 3.3V.   At first that sounds good, but when it stalls, it does not present an open or high resistance.  Boost modules of this design present a straight-through path when they stall.  This could continue to discharge the battery to a level where damage will occur.  The mitigation is the user's ability to monitor the battery voltage, and turn the unit off when the battery voltage is too low, or the players start to behave erratically.
I'm confident the PM GO DJ will make it through my next DJ Job, which is important, as I have a full-paying gig on December 3rd.
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5  Original Projects and Builds / Other Builds and Projects / Re: Poor Man's version of the Monster GO DJ
 on: Nov 22nd, 2022, 2:03pm 
Started by Administrator | Post by Administrator
The Poor Man's GO DJ let me down during an all - day Car Show earlier this month.  For part of the show, I had to switch over to the real Monster GO DJ, which also presented a problem -- I was set up in direct sunlight, and I couldn't see the displays of the real GO DJ.
I finally had to go sound off, unplug the real GO DJ, take it over to some shade, find the backlight brightness setting burried in the various settings tabs and pages, and turn it all of the way up.  I'll note that there is no contrast setting. Even with this done, I still struggled to see the screen of the real GO DJ.  I was not having any problem seeing the screens of the Poor Man's GO DJ under the same conditions.
As it turned out, once the Poor Man's GO DJ charged for a while, I was able to go back to using it to finish out the day.  It ended up only being 2 breif periods without music.  I still got paid, and I got several compliments on the song choices and sound quality.
So why did my Poor Man's GO DJ let me down?  As mentioned previously, the new, color LCD player modules draw a lot more power than the B&W screeen modules used in the original design.
While the charge/discharge module mentioned in the pevious post seems to power the PM GO DJ fine from the internal battery, it does not -- unfortunately -- maintain 5VDC output during charging.
When charging, the output voltage (to the load, not to the battery) drops to several tenths of a volt lower than the input voltage.
Given the length of wire from a 5 V USB charger, and the load of both charging the batteries and running the device, I end up with about 4.7 V at the USB connector, and less than 4.6V for what is suppose to be a 5V supply.
Typically, devices designed to run from a regulated 5 VDC power source have a tolerance of 5VDC +/- .25V.  So a voltage down around 4.6 won't cut it.  The player modules glitch or spontaneously re-boot.
I should also mention that the +/- boost converter that supplies the dual rail voltage for the analog sections seemed perfectly happy with this input voltage.  The failure is silent -- the music simply stops -- there are no pops, clicks, etc. when this happens.
So I still have the original problem -- I need a steady source of +5VDC at about 1 amp under all conditions.  This should be easy, but I have not found a module that will do this reliably.
Solution space:
1.  Forgo battery power --- After all, I am never going to do a DJ job on battery power.  All of the other equipment (except wireless mics) need external power available, so why shouldn't the player have the same requirement?  I designed the player to run from a battery only because the real Monster GO DJ has a built-in battery.
1a.  Power the PM GO DJ from an internal 5VDC SMPS.  SMPS's with more than enough current capability are redily available, inexpensive, and would easily fit in the current player.
1b.  Simply remove the battery, and rely on the power directly from an external USB source.  A quality USB charger and cable should provide the needed voltage without a problem.
2.  Down - then up again solution -- use a buck converter to drop the output of the charger module to about 4 V then boost it again to a stable 5.1 V.  The chager module would always provide enough voltage to operate the buck, and I have bucks on hand that are rated for the full load current even at 4V.
3. Up - then down again solution -- take the output of the charger module and boost it to ~8 V, then use a buck to make a regulated 5V.  Again, the charger module should provide sufficient voltage for the boost converter under all circumstances.  With a minimum of 4.6 V input, and ~8V output, the boost converter is working at lower currents than it was in the original design (when it was boosting the battery voltage), so it should be running in a more efficient range, and thus it should remain cool.
4.  One additonal Conversion -- Find a buck/boost converter that will reliably provide 5VDC output from inputs very close to that same value.  So far, I have not found this.  Most boost converters want the output to be at least 1V more than the input, and similarly, most buck converters need  the imput to be at least 1V more than the desired output.
5.  By using a very short USB cable, the charger module may provide enough voltage as-is.  I would then power the GO DJ from a USB power source very close to the unit.  If I can eliminate voltage drop in a long USB cable, I may be able to tolerate the drop through the charger chip.  As long as I can reliably stay over 4.8V, I should be good.
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6  Linuxslate.com Reviews & Commentary / Review Discussions / Re: Ailunce HS2/Radioddity QR20/Q900 SDR
 on: Oct 25th, 2022, 10:03am 
Started by Administrator | Post by StephenH
Thank you to this poster for the information.  It is hard to find much info about this radio.  I've had mine for about two months now and really enjoy it.  I have the Radioddity QR20 with V 2.0 HW.  I tried to load the firmware update onto a flash drive but it did not load.  It looks like on the QR20 vesrision the bootloader must be updated the hard way.  I am very nervous to perform this surgery on the machine.  Those jumper wires are very very tiny and it is a very tight space.  I guess Ill wait until i can find someone who can help me.  
Thank you again for all this info!
Quote from Administrator on Jul 4th, 2022, 7:08pm:
This is a quick post to provide links to the brand names for this radio:


Chongqing Guohe Electronics Q900
Ailunce HS2
Radioddity QR20

Note: Ailunce is not a misspelling for Alliance.

A Few Notes:

  • The Guohe Electronics website has improved greatly in just the last few weeks.  Looks like they are getting serious about supporting this radio.
  • While I am making the assumption that these radios are all the same or very similar, I do not know the results of using one brand firmware on a different brand radio. It is possible that different radios do in fact have component changes or boot loader changes.  Using a different firmware may permanently render the radio unusable (brick). See below.
  • I am listing the vendor brands together like this only as a reference.

Firmware Installation Methods:

Q900 Radios that show HW: 2.0 (or later, presumably) can be updated using a USB Flash Drive. Installing a separate Bootloader file is unnecessary at this time.  The DeFuseDemo Software, and instructions that reference it are not applicable to currently shipping versions of this radio (Summer 2022). HW version can be found in the Info App in the Menu (The screen with the Icons).  This also means that upgrading the radio using Linux (or any operating system) is not an issue.  Just copy the Firmware file to the root of provided USB drive (or any USB drive).  Be sure to rename the file on the USB drive to FW-NEW.bin (no matter the version). With the radio OFF, insert the drive into the full size USB connector on the back of the radio (you cannot use the USB-C jack even if you have a USB-C compatible Flash Drive), and turn the radio on.  The firmware update will happen automatically.  Follow on-screen prompts.

Note:  Bin Files and DFU files are different.  Renaming a file with a .dfu suffix to .bin will not work, and could brick the radio.  All new FW files should be provided in the .BIN format.

More Firmware Information:

As mentioned the Chongqing Guohe Electronics website has gone from just a shell to a very nice looking website, including a manual (very similar to the others, but with some additional information) and 2 firmware versions.  The latest software on the Guohe Electronics website is called FW-NEW_2.1.5.bin inside the zip.  My radio said it had FW 3.0.0, so I knew that installing it could result in a downgrade, but I tried it anyway.  Even though the file inside the zip had a date of 24 Jun 2022 (much later than when I received my radio),  I ended up with a downgraded radio.  While I did not test functionality, several of the applications in the Menu (Icon) screen were missing.

While I still chanced bricking, or at least rebrading the radio, the above situation prompted me to try the Radioddity QR20 firmware.  The Raddiodity FW page had a newer firmware still marked 3.0.0, but dated "20220607" -- again -- later than the date I received my radio, so I gave it a shot.

My radio now reports HW: V3.0 and SW: V3.1.1.  (HW: 3.0 is not a typo.  That is what it says.  I assume that refers to a Bootloader version). The radio also retains the Chongqing Guohe Electronics logo and my Callsign at startup, It also retained my programmed frequencies.  I will continue to report FW issues and fixes in the previous post.

Apparently, the only difference between 3.0.0 and 3.1.1 (AKA 3.0.0 20220607) is a fix for a Bluetooth Headset issue.  I am not expecting any other differences/fixes.

UPDATE:  I can now report with some confidence that the Radioddity QR20 firmwares and the Chongqing Guohe Electronics Q900 firmwares seem to be the same.  The Version 2.1.5 FW-NEW.bin from the Raddiodity site and the Chongqing Guohe Electronics page have the same md5sum result.  The Ailunce Firmwares seem to follow a different numbering scheme, and are distributed in .dfu format.

I still suspect that the Ailunce firmwares are for the same hardware. According to some information, the Ailunce firmwares may even be ahead of the QR20/Q900 firmwares.   For one, this site has partially reverse engineered the HS2 firmware, and found several PIN's.  These PIN's are the same as the PIN's in the QR20 and Q900 Firmwares.  Note also that the linked github apparently mentions a V1.4.0 Ailunce

If anyone would like try loading a Ailunce .dfu firmware on their QR20 or Q900, please use the information at the top of this page to create an account, and post your result. Again, please note the cautionary statement above.

Check this thread often, as I will post information about new firmwares as I find them.

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7  Original Projects and Builds / Other Builds and Projects / Re: 7591 Amp Build (from Rowe/AMI R-4359)
 on: Oct 21st, 2022, 8:45pm 
Started by Administrator | Post by Administrator
This project is (kind of) on hold again.
There's nothing wrong with the project, it's just that I don't have 2 decent audio dummy loads.
I had a whole separate project in mind to make an "Audio Tester" that would include dummy loads, but I have scrapped that idea for reasons that I will not get into here.
So why is it "kind of" on hold?  While the Amp itself has been off the bench for a few days, I have been working on the cover for the High Voltage SMPS (The board seen on the top of the chassis in other pictures.)
The original plan was to bend it from a sheet of perforated metal; However, I decided to make it out of materials I already had on hand.  Namely Lexan (Clear Polycarbonate) and steel mesh.

It may get one more coat of Polyurethane, but it is basically complete.  I was thinking of providing some lime green trim (Opposite scheme as the OPT's), but I may just use some green LED's mounted inside to achieve a similar, but more intense effect.
Maybe a "Warning High Voltage" sticker?
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8  Original Projects and Builds / Other Builds and Projects / Re: 7591 Amp Build (from Rowe/AMI R-4359)
 on: Oct 16th, 2022, 9:23pm 
Started by Administrator | Post by Administrator
As Promised, a Couple of Pictures:


  • No High Voltage Cage.  Home Depot was out of the perforated metal sheeting I was going to use.
  • There is still protective masking tape on the top.
  • Front Lens/Bezel not installed -- Again, this is to protect it from scratches, as I continue building.
  • Only the 2 Tubes on the left are the new ones purchased for this project.
  • Not Visible, but the little metal "L" brackets that allow the top to remain stable when the unit is opened are still installed.  There is still a non-trivial amount of work to be done inside.
  • Little Rubber Feet (LRF) installed.  That's kinda like when an airplane under construction has "weight on wheels" for the first time.


Added picture of back panel.
  • Note USB/SPDIF Optical/SPDIF Coax inputs on the left.
  • DAC Volume Knob installed.  Note that this is a digital encoder, there are no wipers, and no audio flows through this device.
  • Only the 8 ohm terminals are currently connected internally.
  • Hole plugs installed.  At this point, it is hard to tell that this chassis was re-used from another device.
  • Hinge brackets to allow easy servicing are visible in this view.  These will be removed.
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9  Original Projects and Builds / Other Builds and Projects / Re: 7591 Amp Build (from Rowe/AMI R-4359)
 on: Oct 16th, 2022, 2:10pm 
Started by Administrator | Post by Administrator
Just another quick update:
The other Channel is complete, and playing music.  I have installed the brand new 7591a's in the left channel, and set the bias.  The amplifier is playing in stereo.
Supply voltages all look good (391VDC ob the plate, and 349VDC for the screen/pre-amp/phase inverter supply).
During build up of the 2nd Channel, I noticed that I used a 3.9K resistor on the cathode of the Channel 1 pre-amp.  I had 1.8K on the schematic, with 2.7K written in as "as-built".  I don't have any other notes or memory of where I came up with the 3.9K value, so I built Channel 2 with 2.7K.  I like the voltages around the Preamp/PI better on Channel 2, so I will change Channel 1 to 2.7K.
With the built-in Spectrum Analyzer disconnected, the amp is dead quiet in idle.
With both channels working, I now have a full load on all power supplies.  Nothing but he power tubes are getting hot.  
I am still suffering from Dummy load anxiety, and I don't have a pair of dummy loads appropriate for continued feedback tuning.
My intent is to complete final assembly (Chassis sides, handles, etc.), and in the mean time maybe-- order some dummy loads.
Pictures soon.
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10  Original Projects and Builds / Other Builds and Projects / Re: 7591 Amp Build (from Rowe/AMI R-4359)
 on: Oct 15th, 2022, 2:46pm 
Started by Administrator | Post by Administrator
Here's a Minor Update, Cross Posted from AudioKarma.org, with edits.
Engineering is always a compromise.
I don't like compromise.
...So I compromised.
Many articles debate the value for the Grid Bias Resistors for 7591 based amplifiers -- Particularly Fishers, but this applies to other grid biased 7591 amps, too.  Many of these articles suggest installing 220K, or even 200K, with the lower values helping to prevent bias run away. So I had previously installed 200K Grid resistors.
However, I felt that the Amp (only a single channel at this time), was not putting out the power that P-P 7591's should produce -- probably because the Phase Inverter was being loaded down by the 200K Grid Bias Resistors.
I didn't think that the change from 200K to 220K would make a lot of difference on the load on the PI; But going to 270K worried me, especially with my experience with (used) 7591 family tubes.
240K is also a value for Metal Film Resistors, and an assortment pack I bought from MPJA contained this value. <-- Yes, that's an unsolicited plug. 2W is overkill for a grid resistor, but 2W resistors in the values included in that assortment have lots of applications in Tube Amps.
So based on totally empirical "guess the number", I installed the 240K resistors.
The amp is definitely making more horsepower with theses resistors installed.  For all you Fisher owners, and other Owners of 7591 based amps that may be worried about run-away tubes, but don't want to hurt your sound, 240K may be the value for you.
I also changed the diodes on the Bias Board to High Speed Glass Diodes that are more appropriate for the High Speed Switching PS that is providing the 18VAC for the (-) bias.
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