Tuesday, August 30, 2016

5LO38I CRT test


Having this CRT for some time, never tested it, so last weekend with the new soldering iron was the right time for it.




Honestly can't remember for which project I got it, in any case it will be useful in the future.. so I hope,

Power supply was based on this diagram:



From this site:
http://danyk.cz/osc.html

Added some discharge resistors so it unloads faster, even so it would take around 10m to go to 0v.

The brightness and focus control diagram:


From this reference:
http://www.emartinka.cz/index.asp?IDKategorie=9&IDClanku=18&Akce=clanek

Didn't used any circuit for testing the deflection but touching with a long wire is enough to cause deflection, so it's working also.

I might need to tune the controls and power supply since the dot is a little too big, don't know exactly what is the relation between focus voltage differential from the electron gun and the dot size, sure it's related.



The box it's standard soap box in plastic so I'm not tempted to touch the circuit while it's operating. If I finish the project it will be for sure placed in a more attractive enclosure.

Internaly:

Didn't had an isolation transformer 230/230 so used an 230/12 connect to a 15/230v. I had my shares of electric shock's and will no risk touching a rectified point directly to mains.

The controls:
The rectifier board:

upside down on the box so the electrons can drop easily...

And the connection to the CRT pins, this is the best way found since I had no holder for it, no mess with solder and quite isolated:


For reference, additional sites with more information case you want to build  a scope based on this CRT tube:

http://www.labguysworld.com/ES_CRT_DEFLECTION.htm
http://users.triera.net/zupanbra/osciloskop/Mali_osciloskop.html
http://www.webx.dk/oz2cpu/clock-scope/scope.htm

The technical details of the tube:



Have a nice day!


Sunday, August 21, 2016

Replacing the Maplin N78AR solder station Iron

One of the first things I bough when got to Ireland, three years ago, was a soldering station.

...Well it's not technically a solder station it's more of a soldering iron stand with some control on the iron power. Similar to a light bulb dim circuit.

In last few weeks the soldering tip was getting completely destroyed, normal after 3 years of intense soldering, I went to replace just to find out the retaining nut was completely stuck and in the process I broke the internal heating element.

Since there was no spare irons on sale for the station model, went online and spoted a vey similar one, tough less powerfull, 30w, the standard is 50w.
My guess it's the same manufacturer and then re-branded.





On the left is the new one... by this time I had removed the cable from the old one to prevent any accidental connection since internally the heating element wire was broken.

Replacing was just a matter of connecting the new soldering iron cables.

I reused the stress release rubber from the old cable
 The station has a retaining slot for the stress rubber, nice build touch.

Since I only have one working soldering iron could not solder the contacts of itself (I could but not safe to do), so they were very well wrapped and isolated.




The internal control circuit is a very simple one so no change was needed.

To open the "station", remove the 4 screws bellow the rubber feet.
Overall I find it well build. For the price and if you don't need anything fancy it can't go wrong.




Now I can go back to melt some solder.



Have a nice week!






Monday, July 18, 2016

FT-307 / FT-107 Internal power supply connection to 230V

I'm now in holidays in Portugal and finally could see the Sommerkamp FT-307 (Yesu FT-107) I bough last time. If you don't know the story,  bough a non working unit/unknown status some time ago and asked a friend to collect and keep it until my return.

Well, the radio is as was advertised, non transmitting and not tested after some smoke left the equipment during transmit.

I powered it on as soon as received the equipment and it's OK receiving but no transmission. Here's the first pictures:




Now, the equipment was set up to use 220v on the internal power supply, currently mains is at 230V so I needed to make the changes before continuing testing.

I was surprised how easy was to make the change, that is working inside the radio, here's the process:

1- Remove the top cover (you need to remove the handle bolts also), no picture since I'm sure everybody already did this to a radio at some point in time.
This step is only needed as a helper to check the internal routing of the cables on re-assembly.

2- Remove the 6 bolts from the back cover:

3- After the cover removed, remove the 4 fixing bolts from the PSU unit to the chassis:

4 - ...then gently pull the PSU unit and remove the 4 bolts securing the gridded top cover to expose the connections:

 5- Previous picture shows the 220V connection... next one already with connection on 234/230:


... that's it, two solder points changed, one is the "jumper" and the other the "line" both from 110 to 117.

Additional notes: the diagram and the vcc as measured on the radio meter:




Have a nice week!



Tuesday, July 12, 2016

Arduino frequency counter

I needed a frequency counter with serial output so an Arduino can count and process, then I realized that the Arduino can be used directly for counting in the range 0 to 8Mhz.
Code and lib is from this reference: http://interface.khm.de/index.php/lab/interfaces-advanced/arduino-frequency-counter-library/

Here's the diagram:

 The oscillator part (on the left) was just for testing if was working, if standalone input is "F_in" on diagram.
The serial out from the Arduino looks like this:


The input signal on D5 of the "Nano":


...and as curiosity the signal on the oscillator:

...not the most beautiful but enough for testing.

Code is this one:
 // ----------------
 #include
// counter code from here: http://interface.khm.de/index.php/lab/interfaces-advanced/arduino-frequency-counter-library/

unsigned long frq;

void setup() {
  Serial.begin(9600);        // connect to the serial port
  Serial.println("Starting");
}

void loop() {
  FreqCounter::f_comp=10;   // Cal Value / Calibrate with professional Freq Counter
  FreqCounter::start(100);  // 100 ms Gate Time
  while (FreqCounter::f_ready == 0)
  frq=FreqCounter::f_freq;
  Serial.print("  F: ");
  Serial.println(frq);
  delay(20);

 //-----------------


Things changed, don't need this part/project any more, in any case it stays for future reference.

Have a nice week!


Sunday, June 26, 2016

SP Road Bangalore

Back from India for over a Month, not much on builds, let's say... on "successful" or useful ones.

In Bangalore I had the idea of going for some shopping on SP road, basically the place where you can get almost everything related to technology.
Unfortunatly on my journey there on a Saturday morning everyone and I mean everyone in Bangalore had the same idea, I don't like crowds, besides that, India was experiencing a heat wave, even for for me it was going way above my limits. In the end just drove by and didn't left the car (there was no free space for parking either).

Second weekend we drove by also on a Saturday only in the afternoon... the same scenario so I just gave up...

Some pictures are better than words:









..an incredible place never the less.

Have a nice week!



Sunday, May 01, 2016

Home of the "BITX" - India

As the title "says" I just arrived to the home country of Farhan, VU2ESE, the "inventor" of the BITX transceiver and was thinking how nice would be to build one (another) with components sourced locally. Let's see if on my free time I can walk around the electronic market zone.

Meanwhile for some one just arriving from Ireland, it's hot! Hot as in at least more 20C than on the "island"... and that is just for the lowest temp here.

Some pictures of the landscape:




Have a nice week!





Sunday, April 24, 2016

TA7642 / ZN414 / MK484

All 3 references in the title are small, 3 pin, AM receivers in a chip with minimal external components.

I remember seeing then in schematics at electronics magazines many years ago, somehow expensive (the Ferranti ZN414) at that time, so, never got one. Until now, the equivalent TA7642:


... previous image is the testing board, run with the following schematics and it worked:

..my small changes in red. During the night with this it was possible to get some stations and also a beacon, I guest the cap/coil tuning range was going inside the LW band. The coil, don't remember where I got it, probably from some scavenged radio.

Tested also with variable capacitor to ground:
..was about to try with the varicap in place when I "fried" the TA7642 by touching the input with the soldering iron while powered on, bad luck and crappy iron, pretty sure the varicap version will work too!

Anyhow it's a funning litle device, good enough for a very simple AM receiver.

Have a nice week!