23 September 2010

FT817 remote, on the way... (2)

A short update on the remote control project.

A preliminary version of the circuit layout is working on breadboard. It includes an ATmega168, a PCF8574A TWI I/O expander, matrix keypad and LCD display.

I have been able to read the keypad using interrupts and display keypress on the LCD. I have been able, with another piece of firmware, to read data from the FT817 and display it on the LCD.

Now it is "just" matter of putting both codes together and working on a firmware logic that combines a continuous frequency display, keypad input and a sort-of menu driven function selection.

20 September 2010

5W LED vs. halogen spotlights

I wanted to compare a power LED with something "similar", like a spotlight. The sink of my kitchen, sitting in a dark corner, was found to be an optimal location. Moreover the cooking area has two 20W halogen spotlights. Since they are next to each other, what a chance to compare them directly!

I took a wall-wart power supply, said to output 9Vdc, 1A max. I measured it under load to be at 10.3Vdc. So with my surplus power resistors summing up to 12.7 ohm, I could drive the LED at about (10.3-5.9)/12.7 = 0.34A (measured 0.32A).

The result is shown in a short youtube video, composed of few pictures.

As a practical result, the sink area is very well lit even at just 2W input. The cold white light gives an unreal look to the inox sink, but colors are not distorted.

The heatsink has been equipped with two thin magnetic strips (superglued), so that the installation is not permanent.

16 September 2010

FT817 keypad has new website

I have spent a little time restyling the corner of my website dedicated to the external keypad for FT-817 (FT-857, FT-897). I hope the new look delivers all information in an easier way.

14 September 2010

5W LED and heat

LEDs were the first components I fell in love with, when I was a 10 years old or so. The (recent) introduction of high power LEDs (1W, 3W, 5W, ...) has tickled my curiosity again.

I know from their datasheet that they have a rather small angle and need heat dissipation.

The shop in town offered me a cold white 3W LED for 10€: too much for an experiment. The Net comes handy, with a 5W LED at 3.5€ shipped from China.

It's from "DX", part number sku.4516.

The LED is soldered on a star for easier mounting on heatsink, and should work at 7V, 0.7A. My sample has a forward voltage of 5.9V only (out of specs?!), but it's really like having a star in your room, even at lower current drives!

With a combination of power resistors and a wall-wart supply I managed to run it at 0.32A, that makes about 2W input. Far from the specified 5W, but it does heat nevertheless! The heatsink was donated by a TDA4866 found in my collection of unused boards and for a very lucky coincidence it has threaded holes 20mm apart!! Just perfect for mounting the star!

By the way, if you need a TDA4866 contact me :)

Heat. After the initial warmup, the LED+heatsink reaches about 40°C at room temperature of 25°C. Wow, and I'm running it at half power!

In the next post I will show a possible application of this LED, and the comparison with two halogen spotlights in my kitchen.

02 September 2010

Looking for a repetitive speed moving object, at home

I own a Canon Legria FS200 low-end videocamera and I am not satisfied with its recordings quality. The same happens on an older Panasonic. Both of them write on an SD card. An older Sony MiniDV produced much better results to my eyes.

The problem is evident with moving objects: they leave a "shadow" behind them. It's more or less the same effect of scrolling text on slower (~= cheaper) LCD TV/screens, that becomes unreadable.

With a colleague we tried to imagine the technological culprit, be it the slow CCD sensor or the videocamera processor or even the SD card speed.

Speaking of the FS200 only, it has three recording quality settings: LP, SP and XP. They are equivalent to 3, 6 and 9 Mbps. Is this the data rate from the CCD to the MPEG processor, or the top writing speed to the SD card? Probably it's the latter since the user's manual states that the FS200 uses VBR encoding.

In order to get closer to a plausible answer I need to create a relative speed between the camera and an object that is repeatible an infinite number of times. The speed must always be the same, so that it's possible to evaluate artifacts in the recorded output (on a CRT screen, if possible!).

Excluding all human being movements (non-repeatible speed) and those controlled by a human being (like a car), I came up with these constant-speed sources readily available at home:
  • an R/C car at full steam after the initial acceleration distance, within few runs of fully charged batteries
  • the swinging weight of a pendulum clock within a short timeframe (say, 1 hour or so)
Is there something else at home that can move at constant speed as many times as we want? Note: the seconds hand of a wall clock moves too slow IMO. I also neel the amount of light to be equal for each recording.

The experiment will be as follows:
  • mount the camera on a tripod and point it to the moving target path
  • record the moving target at each recording quality settings
  • change the SD card to a faster/slower one and repeat the three recordings
  • compare on a fast screen
The pendulum clock makes this experiment last only a couple of minutes, but it is at my parents' place...

01 September 2010

FT817 external display for transverter

Before I start to work at the keypad+display device for FT-817, I warmed my neurons with a simpler programming task: make the external display useful for users of (microwave) transverters.

It started with a suggestion on the 817keypad reflector when I asked for feedback on the simple remote display last Spring. Now I have a working code filling 100% of ATtiny2313's program memory with the following features:
  • read the transverter local oscillator frequency from the 817 with 10 kHz resolution (in case it's not set to x.000000 MHz...)
  • store the transverter L.O. in EEPROM for power-off retention
  • show the output frequency with 1 kHz resolution
  • all frequencies are displayed in kHz (sorry, too much code needed for a nicer format)
Watch a preview video on Youtube! The code has already changed since the video was shot: now all known operating modes are shown, and "kHz" string on the lowerline is preceeded with a space character.