Saturday, February 10, 2018

RTL-SDR Dongle interference shield/filter

Happy New Year!
I'll try this year to post more project's, (at least one for each month) and some more simple ones in the middle, that including the failed experiments (I do have them).

Said so, here's, with some delay, the first post for this year!

I had the RTL-SDR USB dongle for some time working but wanted to box it up and placed together with the Raspberry Pi already boxed up.
In the process wanted to eliminate some of the noise it was receiving. Keep in mind that even with noise it was working acceptable (just wanted it mostly for ADS-B and possible AIS reception).

So, decided to do some simple filtering and placed it on a full metal box.

In order to know the filter/shielding was working correctly, that is, the design was improving reception I used the QspectrumAnalyser Linux software to get the signal data in a small band subset and then compare on the several stages during filtering/boxing.

The final result of the build is this:

The noise reduction part is by the end of the post.

Here's already with the Raspberry Pi:
And the live feed with a random piece of wire as inside house antenna:

During build:

After connecting to the Raspberry was getting USB disconnects but not if I used it on the Laptop, after twisting together the USB signals cable (green and white ones) it stopped doing the behavior.

And fully boxed:

Now the good part, the schematic for the filtering:
I was looking for ideas here and here , were not tested since I started building the above circuit and it worked first time, to be fair there's nothing that can go wrong with it.

Here the several stages of interference reduction:

1 - With Just a 100uH in series with the power positive:

 2 - With the output capacitor after the inductor, we can see a big reduction:

3 -Here's me holding the USB ground terminal to the box, I am the antenna!
4 -Then soldered the USB ground to the box
5 - With the full PI circuit, much better:
6 -With everything connected, except for the top lid of the box.
7 - Final signal levels with box fully closed:

Additionaly some experiments in logging data from the dump1090 software:

I'll probably do in the future a a small post on that.

In the mean time have a great 2018!

Sunday, December 31, 2017

Egg beater fix

Friday afternoon....going to prepare dinner, egg beater is needed.... it works first time and then bang.... after a days work troubleshooting I don't need more of it :)

There are only 3 possible faults for a mains powered device:

1 - No power
2 - Open circuit
3 - Short circuit

There was power and there was no short circuit, leaving the open circuit possibility, in fact it was immediately confirmed since no resistance was measured from the power terminals... I only hoped it had not been a short on the engine windings causing the open circuit.

I confess that opening was easier than closing in the end, mainly due to mechanical interlock of the eject mechanism.

Here's the fault....

..on the speed/on/off switch, since it rotates (the transparent plastic part, along with the center washer) the wire broke at the terminal (mechanical stress).
In the picture was already in place for soldering, should last another year or two.

And pictures in the process of finding it:

 ... Sabichi least the electric motor looks reasonably built.

Just looked their website (, that's not bad since most brands are just a sticker:

 ".....with one mission – to bring fantastic quality homewares to our consumers in the UK at a great price. We haven’t looked back since...."

.....Marketing.... it just means: bring Chinesiun or Eurocrap lower grade devices, re-brand and sell for the highest possible price...
Anyhow, even in our hobby we are seeing the same...

Have a great 2018!

Friday, December 29, 2017

Bench power supply ( part I )

This is part I from the build of a small bench power supply.
It's going to be 3 supplies in 1, one from 3-19V (build bellow), a 5v USB output and a variable dual rail implementation of the LM317/337.
The first one, already finish, is using an LM723 implementation, nothing special, just picked the first schematic that seamed viable and built it.
This power supply it's just to avoid having to resort to the 13.8V one from the radio since it will be used for small circuits testing.

Here's the outcome (left size finished minus buttons and voltage display, latter on that):

The USB out (in the midle) it's going to be useful for testing Arduino projects without fear of frying the USB port on the computer, it's just a garden implementation of the LM7805 with two 100nF caps on the input and output.

The schematic that I used for the variable supply was the one bellow (from here):

I used a TIP3055 and TIP31 instead since I didn't had the specified ones, the 600 Ohm resistor was replaced with a 680 one.

Bellow a similar schematic with more comprehensive details of the current and voltage controls (from here):

Inside stays like this:
More details with the TIP3055 heathsink (piece of metal) in place:
and the view to the front panel back side:
The box used was one on sale on the local electronics shop and even include a transformer inside, the only downsize was that you had to build your own front panel, nothing some PCB and elbow grease would not sort out:

Not perfect but works. Bellow another picture during front panel build:
The switch most to the left enables or disables the output, handy if you see something smoking while testing and it cuts faster than the main power switch due to charge on the filtering capacitors.

Enjoy the weekend and see you probably next year!

Saturday, December 23, 2017

OS-5020, Kiotto, LG, EZ, Oscilloscope - Info and placeholder

I have a broken Kiotto OS-5020 to fix, that was my first oscilloscope,  suspect the problem is on the power supply. Making here a placeholder for information related to this scope while I don't have the opportunity to fix it (it's in Portugal).

In the past I tried to reach the local distributor in regards to get the schematic or additional info but got no reply for the two email's sent... so on the good Portuguese tradition.. have a finger and don't count with me to get any more equipment from your business.

I already did before some troubleshooting to suspect the power supply even without schematic but to no success at that time.

This scope comes with many different brand names, here's some examples from the web:

Kiotto (local Portuguese re-branding by "Niposon" distributor):



The schematics:



Here some good description also with schematic in multiple pdf's:

Another slightly different unit (9020) but I suspect very a similar schematic:


And the OS-9020 version with similar symptoms but same resolution:


 The "common" problem with the unit looks like on the negative rail power due to a resistor/fuse, that causes a smaller horizontal trace and no vertical deflection.
In my case I eared a small "bang" when the issue occurred, at power on of the unit, but never found any damaged component on a first glance.

Bellow some posts with matching images (from the post) on troubleshooting of the power unit.

Exactly the same power supply as mine (as far as I remember since last time I touch it, was 5 years ago):

Voltages on the main board:

As soon as I have the opportunity/time will continue the repair on my unit and update here.

Wednesday, December 20, 2017

MAX6675 termocouple reading

Got this little chip already assembled as a module and with a type K thermocouple included, idea is for some other project and/or soldering iron temperature meter.

Initial testing showed max temperature of my iron tip in the rounds of 180C, it takes also a little to overcome thermal inertia and I guess needs calibration since the melting point  of 60/40 solder (used) is 188C and probe was showing 181.
Other methods of calibration could include freezing and boiling water.

Here's the prototype:

Reading the soldering iron temperature (not exactly a scientific grade measurement):

The code used (changed from the library example)  with output on serial port:
// this library is public domain. enjoy!
//name=MAX6675 library
//sentence=Arduino library for interfacing with MAX6675 thermocouple amplifier
//paragraph=Arduino library for interfacing with MAX6675 thermocouple amplifier


int thermoDO = 4;
int thermoCS = 5;
int thermoCLK = 6;

MAX6675 thermocouple(thermoCLK, thermoCS, thermoDO);

void setup() {

void loop() {


I also measured using the built in sensor/thermocouple on a JBC type C245 tip showing different values from the K thermocouple included with the MAX6675 module (also not a good idea to use simple wires from the probe to the chip).

 Here's measuring the solder melting point (or higher than that, due to thermal inertia)

Check the size difference between the Maplin "garden variety" type soldering iron and the C245 from JBC. Bellow also an example on how small the JBC tip is:

...and no, I didn't bought the full station, just one tip to "play" around. Looks nice but hard to justify the price and I guess the tip's won't last as long as regular heating element's.

Connection to the Arduino (I used the "nano") from the MAX6675 module is as follow:

DO = pin Digial 4 (D4)
CS = pin Digital 5 (D5)
CLK = pin Digital 6 (D6)

Interesting the module I got has the wrong polarity for the thermocouple printed on the board, that is; one side of PCB shows "+" the oposit side shows "-", If you connect wrongly the thermocouple, the temperature output from the code will show decreasing when it's getting warm and also near freezing point at room temperature (assuming you are not in the north pole doing experiments.....)

Have a great season.


Monday, November 20, 2017


OK, this blog is mostly building projects but sometimes I like to share other stuff.

Got this inside an order of ceramic variable capacitors (10-60pF), from a seller in Bulgaria. This is the second time I buy from the same vendor and if I remember in 2014 I also got something other than the normal goods inside, always a nice touch!

Have a nice day!

Sunday, November 19, 2017

Raspberry Pi in a new box

Some times I just want things done, on some other occasions I prefer to do it correctly...or at least I try!
 That was what happened to the previous box for my Raspberry Pi, just needed some cover so devised this cheap box:

Now it's time to improve a little bit and place it on a more definite location, this was what I come up to (still going to include a front switch to disable video and power to the small display):

Inside: the Pi with it's power supply (wall unit without terminals) and one to  power the video screen (the transformer, diode rectifier and an LM7812 using as dissipator part of the crystal filter box that I butchered in a previous post.):

Still not sure on the placement of the screen since it would go nice on the front panel, problem is; being a little higher than the box.

The back panel where the magic happens:

Pi Ethernet port, USB ports, video and power out for the screen, power switch and mains entrance. Might include later on the front panel a shutdown button.

The plan for this Raspberry is to have it permanently connect to an SDR dongle doing reception work and then access it via another computer.

Have fun!