I bought one of those cheap Finrsi tablet scopes from Amazon as I needed a cheap scope to use very occasionally for basic things. Obviously I didn't want to spend a lot of money so this seemed ideal for me and the portable tablet form is quite appealing.
Now a pro engineer would not entertain purchasing one of these but for a hobbyist they should be fine. However I did run into a few issues with it as in the general quality is so-so and the operation of the unit isn't without it's problems.
Since making the video I would like to mention that the bandwidth is only 5Mhz on the 1x probe setting and supposedly 100Mhz on the 10x setting. I should have read that Chinglese manual. Doh. However the bandwidth is really around 20 - 25Mhz as you will see. I do encounter a lot of interference and ringing even at low frequencies which I believe is partly the scope. It does pick up noise even when nothing is connected which is kind of normal for digital scopes but more expensive models have various ways of reducing this. It also seemed to have trouble triggering from the internal 1khz calibration signal.
***The 50% auto trigger can be turned off in the system settings (I found this after encoding the video) and turning this off makes a vast improvement making the scope more usable. ***
The trouble is I don't have any lab quality test gear; I can only compare this scope's performance with an older and more expensive model. I'm also used to using CRT analog scopes however the scope I use at work is a digital scope around 6 years old. I did use the same equipment to test this scope that I used with the scope I borrowed from work and didn't encounter any of the issues shown in the video if that's anything to go by. My Keysight DMM has a frequency counter built in so I was able to verify the accuracy of the scope's frequency readout which is spot on. Voltage wise, no. It's out by nearly half a volt with a 5V p-p signal input.
Would I recommend this? Well depends on what you want to use it for. Basically if you want this as an instrument that can give accurate, reliable readings then no. The voltage measurement readings are way out for a start.
However if you just want to check for presence of a signal or not or want it for audio use and possibly TTL logic / CMOS circuitry then maybe, yes it could work for you. But I really would save up and get something better; you need to be spending at least £300 for an entry level scope.
It's a shame really as the tablet format is really good as it's portable and much easier to use on the bench without having wires everywhere. I really want to like this little scope but I just don't want to trust it. Maybe it will get future firmware updates but there doesn't appear to be any way of easily doing this unless possibly it's updated via USB? Something I could look into.
***Further update***
I've since changed my mind about sending this back. I may look at adding some sort of shielding and do some further testing with it as I believe it isn't that bad just not that good either. But there is always some doubt in my mind if this thing is showing me the right readings or not. I'm aware the voltage readings are high but I can account for that.
#ads1013d
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https://www.youtube.com/watch?v=SoCd2nu_bnA
HiFi enthusiasts often "burn in" their new speakers using a variac to exercise the speaker cone which some say improves sound quality. I bring a whole new meaning to this and show what will happen if you push it too far...
18 volts was all it needed to blow these 15 watt speakers up. A short but silly video.
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https://www.youtube.com/watch?v=PIIz-BUxEco
In my previous videos I spoke of buying some scrap electronics namely 3 x numeric wallboards and a scrolling wallboard which appear to have come from an insurance company's call centre. These units show the number of customers waiting in the call queue and how many calls have been answered.
I power one up and take it apart to see what's inside, how it works and if there are any parts to salvage that could be used for electronics projects.
Edit: the supply voltage to the LED modules is unregulated 9V (measured 10.8V displaying 5 zeroes) not 18 as I'd assumed in the video. The more segments that are lit the dimmer it gets; this is apparent in test mode where it scrolls through 0-9 and A-F on the displays. LED segment current is around 5mA. They also haven't used a bridge rectifier; instead used two diodes on each of the secondaries of the transformer giving half wave rectification. The DC output of the two diodes are paralleled together giving more current which is fed into a 7805 in turn supplying regulated 5V to the microcontroller and logic chips. There is noticeable 50hz flickering on the displays.
Video of the scrolling message display https://youtu.be/2TwnPE5FpQI
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https://www.youtube.com/watch?v=z9JJ6MQDJj0
An old Samsung tablet with a broken charging port gets opened up carefully with a hammer to see if it can be powered without a battery. When the experiment was over the tablet was destroyed by feeding way too much voltage into said battery connector and shorting it out.
I then did a durability test using a hammer and drop test.
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https://www.youtube.com/watch?v=AY7bY_yeQA8
I picked up an aircraft black box that came from the failed Nimrod MRA4 project that was picked up cheap on eBay. The "black box" is actually bright orange and has reflective striped across the casing. It is around 20 years old (manufactured 06/2000) and utilizes solid state recording using flash memory as the storage medium.
I was interested to see if I could extract any data from it but unfortunately that was not possible although I was able to power it up as it only needed 28V dc to work. It made for an interesting teardown anyway and now would make a suitable man cave item.
The internal circuit boards consist of a power supply board, an audio processing and compression board, the main CPU board and the flash interface board. The CPU board has two microcontrollers; an 80C51 and an AMD 29200 along with flash memory, ROMS, RAM and the usual stuff. I also dumped one of the ROMS (the boot ROM) and managed to extract some of the serial menu from the code that is sent over the RS232 port on the front.
Upon further inspection this unit has a boot ROM and the actual program that runs the CVR is stored in flash. The application firmware is upgradeable and erasable via the front panel serial port and it appears that it has indeed been erased. Most likely to prevent re-use. I would assume the data storage module for the recordings has been erased too.
Photos of the internal electronics can be found on my blog at https://www.adrian-smith31.co.uk/blog/2021/01/pg-aircraft-cockpit-voice-recorder-black-box-teardown/
Photo of main CPU board showing firmware flash, CPU and RAM used in this unit https://www.adrian-smith31.co.uk/blog/wp-content/uploads/2021/01/PXL_20210215_134859260.NIGHT_-1-scaled.jpg
Timestamps:-
Part 1: Teardown of control electronics 4:00
Part 2: Teardown of audio storage module 12:05
Part 3: ROM dumping and a look at the code 18:15
#electronics
#avionics
#nimrodmra4
#aircraft
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https://www.youtube.com/watch?v=btbiwhJLDLo
I bought some cheap MAX7219 chips from eBay for experimental use in a possible future project. I noticed that they were different to the last ones I bought which were branded Maximi / Maximl which *did* work but with some issues and glitches so they were chucked and replaced with genuine chips which gave no problems. The glitches were LED’s that were lit that shouldn’t be and simply intermittent corrupted display. The fake chips also needed a stable 5V supply and critical positioning of the bypass capacitor. The genuine chips were more tolerant.
I thought I'd give the cheap chips another go so I tested them and found them to work however they were not given a long soak test and they didn’t seem to exhibit the glitches the previous batch did. At least not immediately anyways. As before I will only use them for testing and use genuine components in projects I'd use myself or to sell on Tindie / eBay.
So here is a quick video on how to identify if you have got fake or genuine MAX7219 chips. Might be useful if you have been sold genuine chips and these turn up instead. But really you should be buying from reputable suppliers for production projects; these are OK for hobbyists I guess but if they glitch you will probably not assume the chips are bad. It could lead to lots of frustration.
The genuine chips seen in the video were new old stock purchased from a company selling surplus stock left over from production runs of electronics.
Link to the article on the Arduino forums where these chips were delidded exposing the dies. https://forum.arduino.cc/t/maxim-7219-real-and-fake-compared/226823/15
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https://www.youtube.com/watch?v=2sbrm7k_qd4
My HP OfficeJet 6500A Plus was a good printer when I purchased it. The printer was quick and produced good quality prints. It's not something I used often and every time I used the printer it automatically cleaned the heads which wastes ink. The printer does this by running ink through all the inkjet nozzles into a waste ink pad in order to unblock the jets. Due to me working from home I needed the print / copy / scan / fax features hence why I bought a business class printer rather than a consumer model.
The printer still developed lines through the print which would not clear despite manual cleaning. This consumed a whole cartridge which are quite expensive and it definitely does not like aftermarket cartridges.
I ordered a printhead but after replacing it the printer spent around 10 mins priming the new head wasting even more ink, asked me to calibrate the head which I did. It clunked, rattled and whirred for another 5 mins then came up with ink system failure. Even putting the old head back in didn't fix this.
I wish HP printers did not automatically clean the heads after long periods of not being used. It would be much better if you could clean the heads IF they needed cleaning rather than cleaning just in case. Maybe this is a way to get you to buy more and more ink but no more. I managed to solve this problem permanently so the printer would no longer cost me vast amounts of money to run.
I expected more from a business class device but oh well.
Watch and enjoy! PS. you might want to turn your volume down a little.
#hpsucks
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https://www.youtube.com/watch?v=w9lr5W5GnAA