The useful TL431 chip

I haven’t made any electronics projects for a while now but I was working on some circuits at work that used a TL431 shunt regulator. This chip can be used to provide a 2.5V voltage reference and also 5V with the addition of two 10K resistors between the Ref pin and supply voltage and another to ground. A 470 ohm resistor on the input to the circuit limits current so not to damage anything. I looked at using one to improve the accuracy of one of my previous projects, an AA rechargeable battery tester.

I had made two testers based on completely different designs, the second uses the 1.1V internal reference to calculate the supply voltage which is used as a reference. The former simply uses a 10K resistor attached to the 3.3V out to the vref pin so it is nowhere near as accurate as the second tester I built. The second tester can also test up to 3 batteries at once.

 

Going back to the first tester I will use one of the TL431 chips to provide a 2.5V reference and hopefully that will improve accuracy as the 3.3V supply is provided by the CH340 on this clone and is far from ‘3.3V’. I don’t expect the accuracy to improve by much but it’s gonna be better than using a supply voltage as a reference as these can vary especially with cheap voltage regulators found on the Arduino clones. As the tester will only be measuring 1.5V max, 2.5V reference is enough. Unless of course you wanted to modify it to test lithium cells in which case you would need to configure the TL431 to provide a 5V reference instead.

British Gas Hive Thermostat no signal issues

I recently replaced my home heating controls with the Hive system from British Gas as my old system had developed a fault with the receiver not switching on the boiler intermittently due to a faulty relay contact. The Hive system worked great for about 3 months until the other day when I noticed it was cold and the heating wasn’t working.

Thinking there was a fault with the boiler I had a look but everything was OK. The Hive receiver was showing the green light indicating that everything was OK. However everything was not OK. The hive thermostat just showed “NO SIGNAL” and no amount of resetting both the thermostat nor receiver would make it work. I decided to move the thermostat next to the boiler and hey presto! It worked. Took it back downstairs and no signal again. What was going on?

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Salvaging electronic components from old electronics… Not worth it?

I’ve seen a few websites where other electronics hobbyists talk about where they get their parts from and many do what I did about 25 years ago; salvage components from scrap electronics by desoldering them. I must admit it’s something I do from time to time; when I throw out old electronics I see if there are any parts worth keeping but mostly there isn’t. Some people on those forums desolder capacitors and resistors for re-use; to me this just isn’t worth it considering the price of components nowadays. Also there is the problem that here in the UK and most EU countries it is illegal to take stuff from the dump or out of dumpsters. It is counted as stealing as once you dump something it becomes the property of the city council or waste company. Many companies smash up equipment before disposal to prevent reuse as well.

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What to do with a blown / faulty ATmega328 – Don’t throw it out… It may still be useful.

In one of my past arduino projects I accidentally damaged a Arduino Mega328 MCU (or it may have been faulty to begin with) but I decided to keep hold of it in case I needed it for a very basic project that didn’t need many ports.

The chip’s pins all functioned OK but it had a strange problem; when the serial port was actively sending data or any other pins on port D were being used, some of the other pins were going ‘partially high’ when they shouldn’t. I noticed this when I connected a 7 segment display to the board as several segments flickered or lit dimly when adjacent pins were high. Any attempts at multiplexing or any other high speed manipulation of port D’s pins resulted in some other pins’s output voltages dropping significantly. The display had adequate resistors and I even tried connecting it via a ULN2803 IC to no avail.

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Fake DS18B20 sensors from China sold on Ebay / Amazon?

A while ago I read an article on fake electronic components that are flooding the market with high end audio and hobbyist parts being the biggest targets of the fakers. The article in particular spoke about high end transistors used in power amplifiers blowing or producing nowhere near the gain and / or frequency response expected.

It turned out to be cheap transistors packaged and stamped with a high end part number; sure it worked as a transistor but you wouldn’t want to use it in any equipment as it would likely fail. The popular 2N3055 transistor was also a common transistor made by the fakers which turned out to be a small signal transistor die placed in a TO-3 package. It didn’t say where these were purchased from but clearly they had entered the supply chain from the far east.

Do any search on google for fake ICs and transistors on ebay and you will see what I mean. Even microcontrollers have been faked. Yes there are even fabrication plants that copy genuine parts and mass produce them. These chips often will work OK but do have some problems or do not perform as expected.

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Ebay transistor tester testing

I bought myself one of those cheap transistor testers off ebay based on the Ardutester at https://forum.arduino.cc/index.php?topic=164112.0 which basically is an Arduino project that someone made which the Chinese commercialized and ripped off. It’s actually a great bit of kit but it’s clearly based on an Arduino project that was never intended to be a commercial product.

The Ebay ‘transistor tester’ which does a whole lot more than just test transistors

With the Arduino and good programming and electronics knowledge you can make an end product that rivals a commercial product. Take for example the Ardutester; an open source project that tests electronic components and displays the results on a character LCD. It’s a fantastic project and the designer made all the source code and hardware schematics available for others to make. Seemingly someone in China saw this as a potential to make money, took the source code and improved it then sold it as a commercial product. I’d imagine the creator of the original product would be pissed but I guess there’s nothing you can do about it.

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