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!

Arduino Speaks and Talks

Have an idea for a small Arduino meter and would be good to have the output to audio in addition to a normal display. Specially handy for troubleshooting without constantly looking at the meter. Googling on the various options, found a small library (Talkie) that does basically it without any external shield or component.

Here's how simple it can be:

Just add power... and connect pin 3 and GND to a speaker. If more power is needed, then place an external amp. Audio quality is good enough for the application. Voice is the classic computer tone but there are examples with other types in the library examples.

 Regarding the library, its at: but I was having problems with compilation on my IDE due to type declaration so got this "fork" version from here: that compiled fine.
The result with audio at the first try:

Have a nice week!


Sunday, October 15, 2017

XF-9 S42 9Mhz AM filter from the Telrad board.

On previous post I made a simple crystal tester, that was needed because I was short on 9Mhz crystals and thought that a good place to get them would be the AM filter from the Telrad board. It's referenced as XF-9 S42, 3.6KHz at 3db bandwidth with 560 Ohm impedance.

I was right, there are plenty of them now available, either for USB and LSB:


Inside, the PCB supporting the crystals

 The schematics is more or less like this:
 Interesting, the input goes to the middle of a crystal, first time I see it.

 Another view
 Side view
 It was not that easy to open the box
 The input details, see the terminal going to the middle of the crystal
 The cover, underside and top side.
 The matching numbers to be tested:
 The values

It was not easy to open the filter, I used the "sardine can" method, previously had tried to unsolder the bottom but there was to much thermal mass and still not sure if it would possible.

So, now I have 9Mhz  crystals for the BFO of the boards and for other projects, one of them already take place in the S9 signal generator.

Have a nice week!


Saturday, October 14, 2017

Quick crystal tester

Needed a quick crystal tester, could had lash it up in a little piece of pcb but decided to give it a more robust look and leave it a bit more permanent case is needed again.
Circuit is out of ordinary/common ones and probably will not work with all crystals but for the intended ones it worked, if you replicate you might need a small 20pF cap in parallel with collector and emitter of the transistor, mine worked without.

Here's the outcome testing a crystal:

The counter is a pre-build module with VFD display, couldn't managed to take a decent picture of the display even with a better camera, I was not born to be a photographer...

The terminal connected to the battery was a left over from the exploded battery on the previous post, so some cents were saved.

output waveform:

Some more crystals in testing:

And more pictures:

Have a nice weekend!

Sunday, October 08, 2017

The exploding battery!

Nothing built in the this blog post, instead some destruction!

In Ireland it's common to have in all divisions of a house smoke detectors, I think this is by legislation and mostly because there's a lot of wood involved in construction.
In Portugal, for example, that is not common since most of the houses are cement build and not mandatory.

Any how, on the present house I'm living one of the smoke detectors started beeping, that's an indication about battery status, the detectors use standard 9V PP3 battery for power.

I replaced the battery for a new one, checked the old one and since it's was still showing near the normal value keep it to power some electronics.
In this case I used it to power the S9 signal generator that was siting in the edge of the bench as seen on this picture (except in vertical position):

One of this days, while working at the bench eared a loud bang, initially since the FT-707 is on top of his power supply I tough that it had slipped sideways.... further investigation and saw the battery hanging free on the edge besides the S9 generator, OK it could had slipped hit the bench but does not justify the loud bang similar to a hammer hitting a wood bench....

 Here's what happened in pictures:

 imagine the pressure to crack the plastic.
 and force it outside the cover

 yups, the battery had long passed the time it should be running.
 The front post also suffered and was removed and used, as battery clip, for a project since this ones are easy to solder on the inside. The S9 generator uses one clip from another dead battery.

Bellow the elements inside:
There's is noticeable degradation....

Anyhow, destruction without personal damage is always fun!

Have a nice Sunday!

Saturday, October 07, 2017

S9 signal generator, update

Just updated the S9 signal generator project, placed a 9Mhz crystal that was previously removed to another project, one of the attenuators is now switched so I can have a high/low option and a rudimentary holder for the battery was added.

It's like this now:

 The battery holder it's just a zip tie but makes it much easier to move around the desk without the loose connection. Besides that, it's simple, cheap and effective.

The switch (in blue) for one of the attenuator pad's in-line with the output.

and the "old"/initial version:

Have a good day!

Sunday, October 01, 2017

Test Hook Clip Probe

Have to make some troubleshooting on a tight and crowded PCB so decided to make an appropriate probe.

The hook clips are very small, not extra quality but so far in the initial testing they worked OK.

With the BNC to spring clip adapter on the other end I can easily change between the scope input, the signal generator or even the multimeter without removing the in circuit probe.

Here's the outcome:

...looking at the online prices for something similar it would be cheaper than with the individual components as I did. In any case I  had the components laying around from shoppings.

The only interesting part is soldering and fit in place

That is; pulling he top cap, passing the wire and soldering on the tab bellow (close to the bottom). the top tab will be a strain relief, I left without crossing and crimping over the cable.

Have fun!


New "Telrad" board with filters

New, as another one, I got recently.

This one looks sightly different in terms of components, basically some caps for decoupling an it has some IC's in socket so at least it will be easy to recover them.

The board is this one:

PCB revision is the same as the other (62-211-2600).

Since some components are missing I will probably use it just for getting the filters.

For ther Telrad board I have and about the filters in it you can see here and here in the test jig.

Have a nice week!

Saturday, September 23, 2017

Electronic "variac" / Variable AC power supply

To be fair I was looking for a real autotransformer, since I could not find one at a decent price or in stock on the local electric material shop, decided to build one electronic version that would do the job.
The need is just a way of testing old mains powered electronics devices with increasing input voltage. Another way of doing the same would be with a serial light bulb, in any case that's not "elegant" enough.

Anyway, here's the outcome, basically a shunt regulator between two AC transformers. Circuit is not mine (original from here) I only gave a little adaptation based on experimenting and what I had available.

 Some output values:

Here's the box:
I ended up not placing the voltmeter in the pictures since it would be a very close fit to the box so placed just a small battery indicator, 300uA with rectifier diode and 180K series resistor. The dashes mark 50, 100 and 150V AC.

The transformers were from salvaged electronics. Still visible leftovers from experimenting with other circuit.

Some more testing:

Based on the design and the components used, on a 15W load I cannot output more than 170V, that is enough for now, if I need the real "deal" then would for sure buy an autotransformer with more capacity.

The original schematic from I2VIU didn't gave full regulation from 0 to 220 so I made some small changes (also due to the fact of using different transformer values:
My schematic: (changes are with white background)

On the original page there is one schematic with regulation by feedback and with a comparator, I tried that design but was not having full voltage swing and used an extra transformer.
Here's the one that was tried but didn't suit.

One fact, there is not many AC variable power supplies schematics available on the Internet.

Hope this is useful to someone.

 Have a great day!

Tuesday, September 19, 2017

XR2206 frequency generator

...Looks like I have to build all the projects that I didn't managed during my youth.... back then my preferences were power supplies, audio circuits and transmitters.
In the audio department something useful was an audio frequency generator , unfortunately an interesting project back then used a XR2206 IC which cost'd the equivalent to 6 Eur by today's money, that's not much, it was 30 years ago.
So back then the best I could manage was the finger test and check for audio output...

Recently come across one of those chips and decided to give it a go.

Here's the final outcome

It would be cheaper to buy one ready made... half the fun.
Also added an Arduino frequency counter with bubble display.

Inside plenty of space:

...but not everything fitted on the front panel:

And some outputs from it:

..I didn't used the full potential of the chip, it can do also some modulation but left that as a possibility for the future, it also only outputs AC component on the triangle and sinusoidal output.

Schematic was similar this one with small adaptations:

 In the initial testing of the counter code...

In all fairness, do I need it? No. Did I used it already, No... but less one project in my "youth" list.... If I remember still have a multimeter with the ICL7106 and an STK audio amp to do :)

Have a nice week!