More TEF6606 info

For the circuit that was constructed for testing (based on the Application circuit in the data sheet, the v3 copy of the datasheet is here), the TEF6606 was powered directly via a 9V alkaline PP3 battery (not ideal, because the ic consumes just over 100mA so the battery won’t last long). The 4MHz crystal was just whatever was available from Maplin. The microcontroller and I2C bus was at 5V (powered through MC78L05ACP TO-92-sized regulator).

The TEF6606 exhibits about 60mV amplitude (peak-peak) of RF (about 110MHz) at the audio outputs of the IC. I saw this in the ‘uninitialized’ state, I didn’t check once the IC has been programmed to tune a channel. This was observed on a scope, and I’ve not used a spectrum analyzer on it.

Regarding audible noise (BW limit the scope to not see the RF), I saw about 16mV p-p of noise on the audio outputs of the IC in the uninitialized state. Once tuned to a channel, the audio level of the music (in FM mode) is about 0.9v p-p. It proved capable of directly driving 2×32 ohm headphones, although it is not really designed for that.

With a lack of time and equipment to test it with, as a subjective opinion, the overall quality of the IC is not bad. It is far better than most FM receiver circuits, although it is certainly not in the same league as high-end home tuners. Anyway, it is intended for car hi-fi applications and there it would be great.

Info on the coils:

L1 (290nH):

Use any wire (bare, enamelled, etc – I used enamelled) up to 22SWG thickness (I used 24AWG), and wrap around 5mm drill bit, 12 turns exactly. Then, stretch to 1cm length, and use a little bit of epoxy glue to hold the shape.

L2 (215nH):

Use any wire up to 22SWG thickness (I used 24AWG again), and wrap around 5mm drill bit, 10 turns exactly. Then, stretch to 0.9cm length, and use the epoxy again.

3.3uH power-supply choke on pin  22:

Any off-the-shelf device should be fine. Difficult to tell how effective it was running in the test circuit, but I just used an Amidon FT-23-61 toroid with 12 turns of tefzel (or it may have been kynar) wire which is usually about 30SWG.

Photo of L2 (left) and L1 (right):

radiocoils.jpg

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Simple op-amp based headphone amp

This single-IC circuit is pretty basic but is enough to get the TEF6606 audio up to (very loud) headphone levels.

simple_audio_amp1.jpg

It is just a test circuit, not intended for high quality. There is no volume control, so the volume is on ‘max’ : – ) The op-amp is not bad. The IC was just what was at hand, and with this op-amp with the input disconnected, I hear no hiss through earphones unless I listen extremely closely. However it is poor for being driven from the TEF6606, and in fact it was later found that I could directly connect headphones to the TEF6606, and so this circuit was not needed.

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Implementing I2C

The ATmega32u2 doesn’t have a two-wire interface (as far as I can tell) or I2C, so this method was used to have an I2C bus. The circuit shows the SCL line, and the same circuit is duplicated for the SDA line.

i2c.jpg

Then, the attached code here i2c1.txt was used.

Only the I2C write capability was tested, and it worked fine. The I2C read should work, but it has not been tested yet.

This was an example write, to the TEF6606 ic:


init();

delay_10ms(400);

i2c_start();
i2c_write(0xc0); // write to the tuner's address
i2c_write(0x00); // mode and sub-addr: standard mode, sub-addr tuner0
// tuner0:
i2c_write(0x27); // tuner0: Europe FM, write high bits for freq 98.8MHz
i2c_stop();

i2c_start();
i2c_write(0xc0); // write to the tuner's address
i2c_write(0x21); // mode and sub-addr: preset mode, sub-addr tuner1
// tuner1:
i2c_write(0xb8); // tuner1: Write low bits for  freq 98.8MHz
i2c_stop();

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TEF6606 receiver

As an experiment, I constructed up this FM receiver. It worked first time – no coil adjustments are necessary. It makes it remarkably easy to get it running. Will post more details soon.

radiotest1

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Test probe

This test probe is based on an SMA connector and spare test probe parts:
probe assembled

Side view:
probe_side_view

Parts used:
Pomona test tips: Kit model 6354 (Five different sizes, pack of 10 total)
SMA socket: Tyco 3-1478955-0
PTFE tape (plumbing tape)
Epoxy adhesive (Araldite)
The SMA socket insert has a diameter of 1.25mm

The Pomona test tips are 1.02mm (0.04″), so they will easily fit.
The spring tips are 0.75mm in thickness at the tip end.

There are two long and two short non-spring-loaded test tips in the kit, so up to 4 probes can be made. The remainder six tips are all spring-loaded, so possibly not ideal. However, it is possible to convert them, by soldering them as shown here. This is easy to do if you put a tiny piece of insulation tape over the area that you don’t want the solder to cover. The tip was clamped to a small pair of pliers with an elastic band, to hold it in place while soldering. Afterwards, it can be gently filed if the solder is not uniform (in my case, I did not need to file it, because the solder bump was under 1.25mm in diameter, so it fitted neatly in the socket.

Probe parts:

probe_parts

One of the probes was inserted inside as a quick test:

probe_test_size

The crimp end of the SMA connector was cut off with a junior hacksaw. This is not essential, but I wanted to reduce the capacitance.The end is then filed or sanded to keep it clean.

probe_cut

This is the probe with solder to make it non-springy:

probe_soldered

The probe needs to be insulated to prevent it from touching the shell of the SMA connector. There is no room for heat-shrink tubing, so instead PTFE tape was used. The tape was wrapped around most of the probe from the solder point, and then inserted into the SMA connector:

probe_ptfe

The excess PTFE is cut off with a very sharp scalpel (otherwise it just stretches!), and then  a blob of Araldite was applied. It is hoped that the sanded end of the SMA connector provides a good surface for adhesion. For future probes, I may apply some araldite to the PTFE portion of the center probe before inserting it into the SMA shell.

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XCircuit on Windows

XCircuit is a drawing program ideal for circuit diagrams, but also for other purposes. I compiled it to run on my Win7 64-bit machine.

I followed Step 1, and Step 2 Option 2 (i.e. Compile from source) from here  and it worked well. These were the only deviations that I had to do (I compiled XCircuit version 3.7.32):

Firstly, I needed to select the packages to install in Cygwin. The screenshots in this zip file cygwin_pics.zip shows what packages are needed.

The XCircuit code needed some changes:

1. Change configure.in file: add .a to the end of .dll in two places (see here for details)
2. Add the following line in files.c near the beginning, as a function prototype
declaration:
void output_graphic_data(FILE *ps, short *glist);

Then at the command line type autoreconf -fiv
Then type ./configure

Then, continue with the usual make followed by make install

To launch the program, just start Cygwin terminal, type

export DISPLAY=:0.0

Start the  XWin Server (Start->Programs->Cygwin-X->XWin Server)

In the Cygwin terminal, type xcircuit

xcircuit.jpg

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Diode ring mixer

A picture says a 1000 words.. this is an ancient mixer on e-bay recently, I have one for experimentation. It looks well designed (baluns to keep the mixer balanced, and tight twists), and is from a military device (UFT 721 or 771). Only thing missing is resistors in series with the diodes, to improve the linearity.

The pictures below are detailed, because from them it is really clear how transmission lines should be wound.

A snippet of the circuit diag is also below.

Front of the board:

mixer_front.JPG Back: mixer_back.JPG

Circuit diagram: mixer_cct.jpg  Layout:  mixer_pcb_layout1.jpg

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How to get a desired resistance using standard resistor values

This is easier than expected…

(example)

type “how can I get 2869 ohms using standard resistors” in Wolfram Alpha and  you get this result:

res.jpg

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Programming the ATmega32U2

This is a low cost microcontroller, less than $5 in a qty of 1. ATmega ready-made boards are cheap, around $20, and this variant doesn’t need a specialist programmer tool (just uses USB). The board in the photo is documented here. Another boards that looks just as usable (not tried) is the ‘Minimus 32’ available from http://www.modtraders.co.uk for £12.95.

noogroove

Notes are here, in this guide programming_microcontrollers3.pdf on all the steps. The guide should be suitable for complete beginners (shows how to write code and how to program microcontrollers).

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Quad FET mixer

Saw this mixer here (google translation – the original website is in Japanese).It looks quite neat!

The entire website has a lot of information, and it is fairly readable in English.

mixer

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