Saturday, December 31, 2011

Health and a Happy new year

Are all my wishes to this blog readers.... and maybe some Eur/USD/GBP/etc to spend on electronic components :)

Here's the light modulator in QRO version...and a better reception "antenna"!

Will post more details next year! It was made today.

Have fun!

Thursday, December 29, 2011

6500K AM transceiver

After the build of the 6500K AM modulator I had to do a compatible receiver. Following the tests with the green LED's I thought they were the right candidates to "antennas"...

before the receiver part build I made a small audio oscillator since it's easier to test with a steady source than a mic, this one oscillates around 1100 Hz.

The oscilator "out" after the pot and 0.22 cap connect's directly to the transmit driver input:

There is nothing simpler, not high performance of course...

Receiving part is just the 2 green LED's connect directly to the input of an LM386 amplifier with 200x gain. Standard from datasheet and no input level pot.

And here the prototype in test:

I got 1 inch range before signal get's to low, in fact signal is just near the noise floor of the LM386, an preamplifier would increase a little bit but using LED's as light receivers isn't the most efficient way of doing things, an LDR or a phototransistor will do a better job for sure. Anyhow it's just a proof of concept....

Have fun!

Wednesday, December 28, 2011

Powered by led's II

Another test with LED's, last time I didn't tested all in the junk box... now I tested the green variety, 2 in series.

The light emitter in the video is my Christmas self present, one LASER pointer that doubles as a small lantern with 2 bright white LED's. Local electronic store doesn't store LASER led's so for 2.5 Eur I had one, just have to disassemble it for further tests in light transmission. The optics su!"# big time but it works for small scale tests.

I did test also a Ge diode with a glass envelop and it did respond to the LASER light giving 21mV, it was an OA90 type I think.

Trying to scale the led's for power harvesting isn't interesting, it's cheaper to buy a small solar panel (from my head calculation) and also other solutions, will try them one of this days.

Monday, December 26, 2011

Electronics - Zener

I post some schematics, some are mine, mostly aren't.... I do understand some basics on electronics but as year's pass somethings are getting forgotten so here's an exercise to remember....

Zeners are tiny little funny devices.... they sit quiet in their room until someone drops them a voltage over their rated value, basically like diodes but on a bigger scale (voltage wise), and then they tend to conduct some electrons.... I never thought it was so difficult to explain what components do..... let's say a zener is the equivalent of a series connection of diodes but connected the other way around, polarity wise.

So let's see a tipical circuit with a zener:

There's a power supply, Vs a resistor R, a zener (that weird diode) and the famous (or not) NE602.

So let's see from an engineering point of view.... the potencial diferencial sum (basicaly the sum of voltages) in a circuit should be "0" (zero)... if not you are creating an energy monster :) but this doesn't matter for the zener subject...just for puting arrows in the circuit case some old teacher of mine sees this...

On we go...

Let's supose we need to stabilize the voltage in the NE602 at 6.2V (just because it eases some math and circuit simplicity). It's also nice to know that the NE602 needs about 2.5mA (0.0025A) of current to work and we have a power supply of
13.8V (most of the time) and our zener can witstand 41mA (normaly more but this is a tested current value from the datasheet and we whant things cool)

Now, we can do this in two ways....

The worst case scenario and the low power scenario...

* The worst case scenario:

Let's say we can have a problem in the power supply and voltage can raise to 24V

We would have to drop some 17.8V in the resistor to maintain 6.2V in the NE602 so our resistor should be (U/I) 17.8 / (Iz + Ine602) = 17.8 / (41mA + 2.5mA) = 409 Ohm...
Power dissipated in the resistor is: 0.77W
Power dissipated in the zener is: 0.25W

So what about when we are runing the nominal 13.8V:
We would have to drop 7.6V in the resistor (13.8V less the zener 6.2V), if our resistance is 409 Ohm then the current is: U/R = 7.6/409 = 18.5mA that is 2.5mA for the NE602 and 16mA in the zener diode.
Power dissipated in the resistor is: 0.14W
Power dissipated in the zener is: 0.099W

* The low power scenario:
Let's save the planet and make low CO2 emissions:
We have a good 13.8 power supply the NE602 consuption is still 2.5mA and we will give just 5mA for the zener (he must do something and still have some margin for power supply flutuation)
Our resistor is now: U/I = (13.8-6.2) / 7.5mA = 7.6 / 7.5mA = 1013 Ohm
Power dissipated in the resistor is: 0.057W
Power dissipated in the zener is: 0.031W
Much less power than on the worst case scenario...
...let's just see what max voltage the circuit can withstand...
We use the same 41mA max on the zener and 2.5mA on the NE602 so voltage on the resistor is R*I = 1013 * 43.5mA = 44V plus the 6.2 on the zener that's: 50.2V
And what if the voltage drops: let's acount only for the NE602 current so the voltage in the resistor is 1013*2.5mA = 2.53V plus the minimum for the NE602 that we consider is 6.2 then the voltage in the circuit should be no less than: 8.73V.


The worst case scenario let's you drop more on the power supply voltage (409*2.5mA is less than 1013*2.5mA).
The low power scenario covers you more on over voltage and has less power consumption at normal operating choose!

Have fun!

Friday, December 16, 2011


The problem of being a home brewer/DIY/having the knack ,on electronics is that sooner or latter you end up thinking you can build/make anything...
One of the first things outside electronics I did was changing the car oil, the sparks and air and oil filter.... it went well...but now it's something different, after watching some Australian "Master Chef" episodes I convinced myself that cooking is easy....compared to harmonics/IP3/band filters, etc...

Here's a local recipe with Mussels (they were also "caught" by me).

You will need:

*Olive oil

Just pour some olive oil, some chopped peaces of garlic and onion on a pan, take it to the stove in a slow cooking position.
As soon as the onions and garlic start to get a light yellow color (means they are starting to get cooked) pour the mussels inside, keep a low power on the stove, cover the pan and let them cook in the steam. Do not put water or salt, they have plenty of salted water inside. Let them cook until they have the shells fully open.

The mussels should be fresh an alive.

Here's the outcome:

It's more of an entry or "tapas" than a meal.

A circuit in the next post... or another recipe!

Friday, December 09, 2011

Mains filter, results

I told you I would write about the mains filter performance after the little VDR issue (blast off).

Well... did it worked?.....did it?......! Can't win all the time!

I'm sure the mentioned filter would work in minor interferences from mains, so the filter will be put in line with the transceiver power line (it's 230V AC powered).

I am not the first one to have issues with switching power supplies since by their nature they are an RF source and this one is a beast, 4A at 20V, normal laptops are have half the rate in current, I guess this computer is not very economical in power consumption.

When removing interferences that you suspect are from a power line there is some simple stuff one can do:

*Put a power line filter: Didn't worked in my case. If the power is DC sometimes a simple capacitor in parallel or an inductor in series will do the trick (low pass filter), capacitors "don't like" voltage change so do the inductors with current.

*Invert the power plug terminals: This will work if the source problem is unbalanced (power line wise)

*Some ferrite cores around the power cables. I've used this method wen using the Si570 RF generator close to some testing boards and it works (Now when using the Si570 I power it up from a separate power supply).

*Build a Faraday cage: Will work as long as that any "air" space in the gaps is smaller than the interfering wavelength... but for my case I suspect the interference is getting in from the antenna cable since the FT-102 it's self is build in a metallic "Faraday cage". I discarded the hypotheses of the interference getting picked by the antenna since it's 10m away, never the less further tests will be removing the antenna cable and the microphone.
I didn't tested yet was to put the laptop power supply inside the filter cage and earth blindage exiting the power cable or even moving to another plug (it's to far away for connecting the laptop to the screen monitor).

*Put and isolation transformer (230V/230V): That is expensive and I would prefer to put again the small computer previous used that I know causes no interference.

Well...the saga will continue....I will test more this weekend.

Monday, December 05, 2011

6500K AM modulator

...Or a "spread spectrum" AM modulator, 390 to 750nm wavelenght, or 400 to 790 THz..... or a white LED AM modulator... now you get it?

Following some LED experiments I wanted to try some light comunication, so decided to do one of the basic forms of modulated light communications, AM, for good or for worst the idea was just to have some fun....

Here's the transmission part, when time permits (I still have a huge backlog on lower frequencies projects) will make some companion receiver and put a mic on this "transmitter".

As you can understand, first I did the schematic and then the final draw on paper...
Any NPN transistor should work but more led's (more power!) will require a more robust transistor, the speaker was just to ear the modulation noise (touching the LM386 input pin), I had no mic at hand.
The pot set's the bias point, and the led should be always on (a steady carrier!?), changing bright by modulation.
LM386 gain was set by an 10uF cap between pin 1 and 8 as standard design.

You can ear noise and see some modulated light in this lousy video:

Have fun!

Saturday, December 03, 2011

Powered by led's

I do like led's but aside the fact they are nice to show power on in circuits I only did some minor tests with them. One of the experiments some time ago was to use a led as a poor and small replacement for a solar cell, yes led's can generate small amounts of energy. Some can sense radiation and other types of PN junction can be nice for temperature sensing (like 1n4148 diode)... normaly components have more than one function you know?! The classic example is a resistor used as a camera flash :) One time action of course!

Next images you have an infrared led, (I think, since I don't remember the specs or even when it was bought) the outer case is light blue and emits no visible light when direct biased.

Here in reverse connection getting some direct sun light.
Two of them in series should give 1.4V althoug on a very small current, this multimeter has 10M of internal impedance but if you put some in parallel you end up with a very small power supply as long as the sun shines...

Here's the "power" from a white color paint!:

Incidently this gave me the idea of using one of this for a very crude Sun photometer.... maybe one of this days...

And in the dark:

This led was the best one I tested, other standard types gave worst results.

Have fun!