27 March 2020

Texas Instruments TI-1500

What I found!!
Texas Instruments TI-1500, that's the third calculator I bought at "Barattolo" flea market in Torino. This one was also battery-heavy, with LED display. There were several versions of TI-1500 back in its days, but I think they all share an enclosed rechargeable battery pack. Mine had two Ni-Cd AA that had gone bad. Quite bad, actually.

The leak has spread almost everywhere on the board leaving intact the display (looks good at visual inspection) and probably the keypad (cannot inspected, but the back is clean).

Without batteries.
After removing the batteries I have cleaned the board with white vinaiger and then water. Since the keypad is blocked to the top shell of the calculator, I had to wash it trying to keep water away from it. Also on one side of the top shell the leak had sneaked under the silver coating and water+vinaiger effect broke it from the inside. This is becoming challenging.

I left it dry on the radiator and tried a power up with an external 2.4V power source. Well, the display showed something but no reaction to keypresses.

I've got too many open projects to take properly care of this calculator. It could stay as is, or it could become a sort of numeric display/clock, as usual.

25 March 2020

Canon Palmtronic 8M

Palmtronic LD-8M 3
After the Litronix 2235, I found a "Canon PALMTRONIC LD-8M 3". That is what tells the battery cover in the back. This calculator was being sold without batteries and with the faux-leather soft case.

After the routine cleaning and some action on the power button, it comfortably showed "0" in the rightmost position.

This is a basic calculator with square root, percent and memory.

Buttons feel OK and don't bounce causing typing errors.

Calculator and soft case.
Battery cover with "LD-8M 3".

Now I own two working Canon Palmtronics, the first being a LD-84. Both came without battery damage. A curious coincidence.

Negative number.

24 March 2020

Let it loop

Being in COVID-19 lockdown gives me the opportunity to be on the air during the day, once work time is over. I tried a magmount 20m Diamond mobile antenna on the East-facing balcony, but I managed one contact with my sloppy CW. Well, RBN receivers had me around Europe. But no contacts were possible in PSK31, neither a report on pskreporter service!

So I moved to something different: a magnetic loop. It had to be build with readily available materials: a hula-loop diameter 70 cm (then not needed to keep it in shape), 4 mm solid coax cable (it's too thin for a permanent loop!), a dual-gang air variable capacitor (two sections in series giving 10-130 pF) and FT817 to tune the antenna sur place.

The feeding loop is just a piece of coax "1/5th of the main loop" long. From the coaxial line, the center goes to braid of the small loop on one side, and the coax braid to the braid on the other side. In other words the feedline is terminated with a 44 cm long loop made of thick wire.

It took me a couple of hours to build. Most of the time was spent looking and implementing a solid mechanical solution for the variable capacitor.

The picture shows the resulting loop. It tunes 30 to 10m. On 20m it is about 20 kHz wide for 2 SWR bars on the FT817.

11 March 2020

Litronix 2235

Litronix 2235.
I had the opportunity to visit Torino's flea market "Barattolo", that is (currently) held every Saturday and Sunday. This is where you can find the cheapest used garbage things. It is not as large as Hrelic in Zagreb, but it shares the same philosophy.

I did not have much time and it was almost time to pack up for everyone. Nevertheless I could find three 1970's pocket calculators, which required a bit of successful price negotiation.

How I got it.
First in the blog show is Litronix 2235 with very curious LED display from 1975.

It felt heavy, a sign that batteries were inside but it did not switch on. Good cosmetic conditions, though. When I removed the battery compartment lid, I saw a little horror show (see picture). One AA battery had even cracked! Nevermind, that is the kind of trouble that I am looking for.

Fresh batteries!
Fortunately the leak had not spread to the circuit, probably because both of the position of batteries within the case and how it was stored. The worst block of salt was on a removable part, that had a bath into pure white (apple) vinegar and a was under tap water. All within 10 minutes time. The plating is now gone, but contact is restored.

Three AA batteries later the Litronix 2235 LED display said hello. It is an 8 digit calculator, but it has a 9-digit display. That's because a decimal point is shown in the position of a digit instead of being subscript intra-digit. What makes it even more peculiar is a dim LED showing that there is Memory content in the upper-left corner of the display.

The LED display. Can you see the small dot in upper-left corner?