NiMH laptop battery from 2001

I got hold of an old laptop from 2001 with the battery dead: what a better opportunity to have a look inside? If possible I wanted to preserve the battery case as much as possible.

A close inspection revealed that the battery case was composed of two parts very closely coupled together. Poking around with a small flathead screwdriver showed that the "weakest" point was the area around the battery connector. And from that point I started pushing and pulling. Few "crack" and some more "ziiipppp" were released before I could remove the lid, which was glued to elements.

The battery, being a 9.6V 4500mAh NiMH looked as shown in the picture: 8 cells in HR-4/3FAU format. All cells measure 1.265V each, which is a sign or them being still balanced somehow, and not dead. A small two-wire component was also found in close contact with two batteries. This could be a simple TC resistor or a more complex device which had also kept count of the number of recharge cycles.

I recharged the battery in place and it got very hot to touch, but charging stopped normally (with the two-leaded component in close contact with two elements). Final voltage was about 11V.

Drawing some heavy current allowed to evaluate then internal resistance developed during the years. At 3A the voltage drop across battery terminals suggested an internal resistance of 3.3 ohm, that is about 0.4 ohm per cell. This is high resistance for a high capacity battery! I wonder if there is a way to reduce it with slow discharge/charge cycles?

One week after the full charge the pack still exhibits 10.6V, about where I have left it, so apparently no cell is dead or leaking current.

Besides being a good paper weight, this pack could be used to power some light-current load despite the internal resistance, with an acceptable and known voltage drop. I am thinking of some power LEDs in series. Other usage ideas welcome.

FT-817 on Mac OSX Leopard, via Bluetooth

I am not a MAC user, but I wanted to test the FT-817 CAT-to-Bluetooth adapter on it.

I borrowed a PowerBook G4 with OSX 10.5.8. Then I searched for a CAT software, and the easier to install was flrig from the fldigi suite. I tried jLog but it complained that "radiocomm.jar are not properly installed" (no results on Google to help troubleshooting). And I could not compile grig either.

I attach seven screenshots of the pairing procedure and sample usage. firig was able to control my FT-817 through the serial port over bluetooth, I just had to use the proper configuration (see the 6th screenshot below).

Provided there is software for more recent MACs, the adapter should work on them too.

Make sure to select the last option, "Any device"

flrig in use and the configuration screen

When you're done, disconnect the adapter

Yaesu CAT bluetooth interface - video

For the Curious and the Interested, here is a short video introducing the wireless (Bluetooth) CAT interface I made for Yaesu FT-817/FT-857&FT-897:

Contact me if you want one interface for your shack.

Frequency Reader with Tuning Knob

The "Frequency Reader" is a stand-alone display with three push buttons that allows to read remotely the FT-817 display data and gives minimal user interaction ability. It is supposed to work on FT-857 and FT-897 too.

As of today, March 13th 2012, the "Frequency Reader" supports a tuning knob which lets you retune the radio remotely. The firmware has been tailored for users of microwave transverters, but nothing prevents using it for the usual V/U/HF operations. Three buttons do:

• USB/CW mode toggle (no action if in a different mode)
• VFO A/B toggle
• tuning step selection

Tuning step is selected using the F.R. knob and reminds FT-817 internal steps.

For interested builders, it should be noted that this new firmware works on a slightly different hardware circuit, on which few connections have been moved around to facilitate the design of PCB.

If a simple Frequency Reader is needed, just omit mounting the knob and step button leaving their terminals open.


Technical insight.
The Frequency Reader polls the radio every second for a frequency change, in case the operator touches the front panel dial knob. If the external knob is rotated, the VFO frequency is updated of a "step" amount every 100 ms. If the knob is rotated very fast, the step is increased accordingly in a linear fashion, allowing faster QSY's.

The knob component, a quadrature rotary encoder, must be selected with care. It should have no detents, or generate one step per detent. If it includes a pushbutton, it can be wired to any of the three required buttons mentioned above.

What is left to do.

• Shoot a short demo video
• Update the website with the new diagram and firmware
• Refine the firmware for general public release

A coil or a lifelong supply of enameled wire

While the supercapacitor and white LED in the handshake flashlight have been used to build a proof-of-concept USB rechargeable flashlight, the coil is now calling for attention. A passive audio filter came to my mind.

On my DVM the coil measures ~22mH for 100 ohm of wire resistance. At 1kHz this means a coil Q of 1,3 (Q = 2 * pi * f * H / R).

I am not into passive audio filters but the Q sounds too low to be useful. The other option would be to use the coil as a lifelong source of enameled copper wire. According to the perceived diameter (not measured, but it is thin) I would have about 1km of wire!

Handshake LED flashlight

Had gotten a couple of these gadgets by General Electrics during Winter Olympic Games in Torino 2006 (that's 6 years ago!): no matter how long I had shaken them, I never saw the white LED lit. Time to take a peek inside.

In there I found a well packed coil into which a magnet slides through with the shake movement; a 4x1N4148 fullwave bridge rectifier, a 0.22F 5.5V capacitor and what looks like a white LED. No resistor in series with the LED, so perhaps it didn't survive the first time 5.5V were applied?

I will check all parts with a DMM, but meanwhile I had the usual bizarre idea: what if I turn the coil into a MW resonating circuit and let the capacitor recharge with the environment RF? Otherwise it will become a simple - and smaller - LED flashlight charged via USB. :-)


Update.  All parts inside the original flashlight worked. Maybe there was a broken PCB trace, because voltage did not reach the 5mm LED. The supercap and the LED have now been wired to an USB plug making a USB-rechargable LED flashlight. It will be featured on this blog in the next days.

23cm downconverter from analogue Sat-TV receiver

If you take apart an old analogue satellite TV receiver you might find leaking electrolytic capacitors and what looks like a shielded RF module.

Well, it actually IS a tuneable intermediate frequency of some sort, working across the 23cm HAM band: 900 to 2000 MHz, more or less. It outputs video baseband, so somewhere between 0 and 5.5 MHz.

Why not take control of the module and turn it into a 23cm-to-HF downconverter? With just one setting of the PLL you would be able to tune around 5.5 MHz of SHF. Yeah, sure.

My IF module contains a TSA5055 "2.65 GHZ Bidirectional I²C-bus Controlled Synthesizer" (PLL), and I²C can be easily mastered with modern microcontroller. But but but ...

The whole IF module has been designed to work with strong broadband signals: the sensitivity of my specimen is -60 dBm (pretty deaf!) and there are no info on phase noise. I would need a powerful RF preamp in front of it, and it is not suitable for SSB/CW work. Project idea discarded.

I am left with the PLL system, tuneable in 125 kHz steps between 1 and 2.65 GHz. It might work as a signal generator, so I will not throw it away, in case one day I will get into the microwave mindset... too bad the prescaler output is not available on one pin, otherwise it could be placed in front of a frequency counter.


Next!

How to find out XTAL frequency with MFJ-259

The simplest way to find out the resonant frequency of a XTAL (or "crystal" or "rock") is to oscillate it. What if you do not have (yet) a simple crystal tester circuit and a frequency counter (or an HF receiver)?

I was in a hurry and I could not assemble a simple oscillator. Then I turned around and saw the MFJ-259 antenna analyzer... would it work?

I picked a known frequency XTAL and held it at the antenna socket: SWR and Z were as if I had connected nothing. Then I swept the frequency close to the stamped one and I could clearly see the impedance dip while passing over. I could actually see two distinct dips, probably series and parallel resonance. Nice!

It is important to look for the dip on the SWR analog meter, not the display or impedance meter. The frequency knob has to be rotated VERY slowly and remember that the MFJ-259 VFO is pretty unstable. Rotate so slowly that, for an unknown rock, you would probably have enough time to heat up the soldering iron and throw together a simple oscillator!