Posts Tagged ‘eBay’

The LM386 Pixie challenge

The Pixie 2 is this minimal transceiver which I and many others have played around with and had lots of fun with. My 80 m version is shown below, but right now it is very popular with some incredibly cheap Chinese ones on sale on Ebay and other places.

The Pixie 2 uses the versatile LM386 amplifier for its audio output. I have shown previously on this blog how its gain can be boosted and how it can implement a CW filter, and also how the muting can be improved. However, during transmission, the LM386 just sits there idle, although it can be used to amplify a sidetone from an external oscillator.

But I’m sure the old 70’s LM386 can do better than that. Despite its age, recently some pretty amazing uses of this chip have been demonstrated. It can be used as a regenerative receiver at least up to medium wave frequencies and it can also be used as an envelope detector/demodulator.

The LM386 challenge is this: Is is possible to implement a sidetone oscillator for the Pixie using only the LM386 with as few other components as possible? The output level needs to be controllable in order to make it comparable to that of the Pixie in the receiver mode.

The best data sheet for the LM386 seems to be the one for NJM386 from New Japan Radio Co. It is, as far as I know, the only one which shows the various muting circuits including the one using pin 7 which I have explored. It also shows the LM386 as an oscillator: both a sinusoidal and a square wave one.

In order for the LM386 to be useful as a sidetone oscillator, I believe that the oscillation must take place in the input circuitry. That seems to be the only way to ensure that the output doesn’t come out at a blasting full rail-to-rail swing as in the square wave oscillator example in the data sheet.

By the way, the data sheet referred to above is also the basis for the improved Spice model for the LM386 that just was developed. It came partly as a response to my complaint over how poor the present one was. Maybe the new Spice model, developed by EasyEDA, could help solve the LM386 challenge?

Ultimate software is up to date

As I have mentioned several times on this blog, I have thoroughly enjoyed WSPR modes ever since Hans, G0UPL came out with the first Ultimate QRSS/WSPR kit.

That means that I have three different versions of the kit. Since Hans has kept on updating the software and even published the compiled versions, it is also possible to upgrade even the old ones.

I have done that and the displays here show the Ultimate 3, the Ultimate 2, and the Ultimate 1 with the latest software.

It is possible to upgrade the chips in-circuit, but I found that it is simpler to remove the chip temporarily from the socket and move it to a simple veroboard with crystal oscillator components. It is connected to my Ebay version of the USBtinyISP.

Car upgrade to LEDs

It was time to upgrade the interior lights in my 2004 Volvo. I got some lamps from Ebay specified as 42 mm LED Festoon, 80-85 lm, 12V. As many others have experienced also, they kept on glowing faintly after the door was closed. But when the ignition was turned off the lamps were completely off also, so there was no danger of draining the battery. Still this is not the way one expects lamps to behave.

One can get more expensive LED lamps which avoid this faint glow, “Canbus error free” seems to be the way to specify this. But mine were of the plain type, and the problem seems to be the leakage current in the FET switches that turn the lights on and off. It is tiny, but enough to give a voltage large enough to turn the LEDs on. An additional resistor load will lower the voltage below that threshold.

This requires a parallel resistor. Some have used 1k, others larger values. I did some trials and found that 10k worked well, while 22k didn’t completely eliminate the faint glow. The advantage is that 10k will only dissipate 18 mW @13.5 Volts, while the 1k will dissipate ten times that. Therefore I could use a small 1/4 W type. I soldered it on the back of the LED-board as the image shows.

The reason for switching to LED is not really to save energy as the savings aren’t that great anyway. The whiter and brighter light is more important as you can see in the image with the LED to the left and the old incandescent lamp to the right.

While at it, I just had to do some reverse engineering of the LED lamps. There seems to be four parallel groups of three series-connected LEDs (the three in a row) giving a forward voltage of about 8.3 V. They are driven via a resistor of 120 ohms in series with what seems to be a bridge rectifier since the lamps don’t depend on being connected in a particular way with respect to polarity.

In total it draws 18 mA @ 12V and 28 mA @ 13.5 V, i.e. 0.3-0.4 W, compared to 10 W for the bulb it replaced. This is not a very sophisticated way of constructing a LED lamp as there is no constant current regulation. The intensity will therefore vary with voltage, but hopefully it will work well here.

QRP kits search on eBay

See http://www.ebay.co.uk/sch/i.html?_nkw=qrp+kit .

Occasionally I look on eBay to see what is on offer. Searching for “QRP kits” throws up quite an interesting selection of stuff, much of it only available by eBay and not otherwise advertised. Some of these items are good bargains.

Touch wood, I have never yet had a bad experience on eBay when buying or selling. Mind you, I would be very careful and not spend too much. Some dealers are good (the vast majority) but there are always a few “bad eggs”.

Caveat emptor.

Solder fumes

Mention Health and safety and its likely you think of some Muppet decides that children need a suit of armour to play conkers (for those not lucky enough to have tried to make a horse chestnut seed the hardest material known to man, have a look here). Back to the point. I’m talking about looking after yourself in your hobby.

Ham radio has some pretty high hazard activities. High voltages, antenna’s on towers, climbing on roofs etc. Recently I’ve been soldering a bit more. Whilst its not likely to be particularly harmful to occasionally sniff in some fumes its probably not going to do me much good either. So I might benefit from a solder fume extractor.

I understand that the technical terms (and we all love a technical term) is local exhaust ventilation or LEV. Still doesn’t sound too complex and thankfully it doesn’t need to be. A fan that sucks and a filter is pretty much all you need, it seems. So do I really need an industrial scale extractor? probably not. So as an experiment I’ve bought a £5 extractor from eBay.

Its an mdf laser cut body with a 12v (computer?) fan. It takes 5 minutes assemble and may or may not need some PVA to hold it all together. I say might as mine was a good tight fit so probably won’t need it in the short term but as it gets bashed about on the workbench it might need some help to stay together.

The extractor is basic (what do you expect for £5) and didn’t come with any filter media. So a suitably sized filter will be needed. Perhaps the same activated carbon you get for cooker hoods would suffice, will need to be sourced. I dare say just sucking it from one place to blow to another isn’t really helping matters.

I could measure flow, compare against standards, determine filter abatement. I say could, because clearly this hasn’t been designed with that in mind and how would that really help? The video below shows you how effective it actually is.

So the conclusion. The hazard associated with occasional solder fumes is probably quite low and the risk is also probably quite low. But a simple device, like this, has the opportunity to remove the fumes from the workbench and at the very least stop them going in your eyes. That can’t be bad.

Here it is in action. Distance between tip and fan is approximately 10cm.

p.s. If you’re really lucky you can hear my daughter homebrewing in the background (what she is homebrewing is anyone’s guess)

Buying batteries on Ebay

Yesterday I wanted to experiment with using a ferrite rod antenna for WSPR. I was using my AA-200 antenna analyzer to try to tune the antenna when it suddenly restarted. I switched it off and on again and as soon as I chose any function the analyzer restarted again.

The last time I used the AA-200 I remember the batteries ran out so I charged it. It appears that after 6 years of use the rechargeable battery pack won’t hold a charge.

AA-200 antenna analyzer and open battery pack

I’m useless at taking things apart but Olga managed to open the battery pack to reveal a shrink wrapped pack of 4 AA cells. I could have ordered a replacement from Strikalite but their price was £20. I found an Ebay seller in Hong Kong whose price was a quarter of that. So for the sake of a few days wait I could save myself £15.

I ordered the battery pack, but this morning there were two emails in my inbox saying “We are sorry to tell you that we are not allowed to dispatch batteries recently for the customs are very strict on exporting batteries.” Is this something new? It’s the first I have heard of it. I’ve certainly bought battery packs (including batteries for handheld transceivers)from China on Ebay before.

The seller has refunded my money (or at least he has said he will.) In the meantime I found a UK seller of Chinese batteries, Vapextech UK, which, while not as cheap as the Hong Kong seller, is still a third of the price of Strikalite. Having said that, Strikalite is still a good firm to go to if you want to refurbish a ham radio battery pack and like me you are useless at taking battery packs apart.

A good deal(er)

If you are a UK amateur and you like Chinese radios you’d probably never think of buying them from anywhere other than direct from China or Hong Kong, most likely using eBay. Ham radio dealers in Britain are widely regarded (rightly or wrongly) as rip-off merchants who work out the price by replacing the dollar with a pound sign and then adding on a bit more for good measure. Their pleas that the UK price includes VAT and the cost of providing a warranty usually fall on deaf ears.

In one of the discussion groups someone mentioned buying a radio from a British firm called Sinotel UK. I went to their web site and saw that they carried several models of hand-helds from China, including a new one I hadn’t seen before: a TYT UVF9 (pictured right.) But what particularly caught my attention was their prices, which were little more than what I have been paying buying on eBay. Their cheapest model, the Vero Telecom UV-X4 (similar to the Baofeng UV-3R) was just £29.99 (yes, a brand new dual band radio for 30 quid.) A UV-5R eas £34.99. The radio that had caught my eye, the TYT UVF9, was £47.99. It would cost me $68.50 from 409shop and I’d have to wait a couple of weeks for it.

I am not associated with Sinotel UK and have not even bought anything from them but if I want yet another Chinese handy to add to my collection I probably will.


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