Easy socket for ZM1001 (and ZM1000 if necessary)

At HAM Radio Messe 2016 I bought a board from Philips PM2421 meter. It mounts 4x ZM1000 numeric nixies and 1x ZM1001 symbol nixie (+, -, ~, X, Y, Z). I tried to reuse the existing circuitry, especially to take advantage of the sockets on board, but there are limitations too: the thousands nixie has been wired only to show 0 or 1 (good for a 12-hour clock) and interfacing to the existing digital logic is not straightforward. On the other hand I could cut traces and feed data to the buffer or to the driver, but then I would have a large board behind the display ... for nothing!

Further down the conversion road I decided to unplug the symbol nixie, that would not be used in a clock anyway. Plan was to try to unsolder its socket, but the dense pinout looks familiar. A quick check at the datasheet reveals that those pins are 2.54 mm apart (or 0.1" if you prefer). Moreover the ZM1001 has only 6 symbols + the anode, so a "modern" socket can be built out of few female headers on a breadboard or custom PCB.

Here's a possible layout (bottom view):

There are no overlapping (red) lines and, if the homebrew socket does not bring unused pins to the board, a simple veroboard can be used:

Veroboard view of the homemade partial socket.

Mind that ZM1001 has two Anode pins, but just one grid, so using just one is fine. At least it looks so, and the datasheet does not suggest against it.

The tube sits well in the socket and has headroom so that pins are not stressed.

So, socket completed. The trick is that unused pins stay floating in the air and are not connected to anything, so routing without a PCB is simplified. The circuit above made with veroboard has copper strips running along its longest side and required very few cuts and jumpers to make it work with the 7441. Also, thanks to the fact that only 6 symbols are used, I can use 7441 outputs all on the same side.

100 years of DST dates for Europe: 2016-2116

As described in an earlier post, I want to try implementing automatic DST switch over in my homemade clocks. At least in those that have a firmware inside.

The plan is to hardcode the switch over date, keep track of DST status in non-volatile EEPROM and check whether a change should be made at power up. The array starts on year 2016, so in case the RTC is reset the firmware must ensure it is taken immediately to year 2016.

So, according to the packing format described in the earlier post, this is how 100 years of DST dates for Europe looks like:

int DSTdays[100] = {
0x25, // 2016-03-27 to 2016-10-30
0x14, // 2017-03-26 to 2017-10-29
0x03, // 2018-03-25 to 2018-10-28
0x62, // 2019-03-31 to 2019-10-27
0x40, // 2020-03-29 to 2020-10-25
0x36, // 2021-03-28 to 2021-10-31
0x25, // 2022-03-27 to 2022-10-30
0x14, // 2023-03-26 to 2023-10-29
0x62, // 2024-03-31 to 2024-10-27
0x51, // 2025-03-30 to 2025-10-26
0x40, // 2026-03-29 to 2026-10-25
0x36, // 2027-03-28 to 2027-10-31
0x14, // 2028-03-26 to 2028-10-29
0x03, // 2029-03-25 to 2029-10-28
0x62, // 2030-03-31 to 2030-10-27
0x51, // 2031-03-30 to 2031-10-26
0x36, // 2032-03-28 to 2032-10-31
0x25, // 2033-03-27 to 2033-10-30
0x14, // 2034-03-26 to 2034-10-29
0x03, // 2035-03-25 to 2035-10-28
0x51, // 2036-03-30 to 2036-10-26
0x40, // 2037-03-29 to 2037-10-25
0x36, // 2038-03-28 to 2038-10-31
0x25, // 2039-03-27 to 2039-10-30
0x03, // 2040-03-25 to 2040-10-28
0x62, // 2041-03-31 to 2041-10-27
0x51, // 2042-03-30 to 2042-10-26
0x40, // 2043-03-29 to 2043-10-25
0x25, // 2044-03-27 to 2044-10-30
0x14, // 2045-03-26 to 2045-10-29
0x03, // 2046-03-25 to 2046-10-28
0x62, // 2047-03-31 to 2047-10-27
0x40, // 2048-03-29 to 2048-10-25
0x36, // 2049-03-28 to 2049-10-31
0x25, // 2050-03-27 to 2050-10-30
0x14, // 2051-03-26 to 2051-10-29
0x62, // 2052-03-31 to 2052-10-27
0x51, // 2053-03-30 to 2053-10-26
0x40, // 2054-03-29 to 2054-10-25
0x36, // 2055-03-28 to 2055-10-31
0x14, // 2056-03-26 to 2056-10-29
0x03, // 2057-03-25 to 2057-10-28
0x62, // 2058-03-31 to 2058-10-27
0x51, // 2059-03-30 to 2059-10-26
0x36, // 2060-03-28 to 2060-10-31
0x25, // 2061-03-27 to 2061-10-30
0x14, // 2062-03-26 to 2062-10-29
0x03, // 2063-03-25 to 2063-10-28
0x51, // 2064-03-30 to 2064-10-26
0x40, // 2065-03-29 to 2065-10-25
0x36, // 2066-03-28 to 2066-10-31
0x25, // 2067-03-27 to 2067-10-30
0x03, // 2068-03-25 to 2068-10-28
0x62, // 2069-03-31 to 2069-10-27
0x51, // 2070-03-30 to 2070-10-26
0x40, // 2071-03-29 to 2071-10-25
0x25, // 2072-03-27 to 2072-10-30
0x14, // 2073-03-26 to 2073-10-29
0x03, // 2074-03-25 to 2074-10-28
0x62, // 2075-03-31 to 2075-10-27
0x40, // 2076-03-29 to 2076-10-25
0x36, // 2077-03-28 to 2077-10-31
0x25, // 2078-03-27 to 2078-10-30
0x14, // 2079-03-26 to 2079-10-29
0x62, // 2080-03-31 to 2080-10-27
0x51, // 2081-03-30 to 2081-10-26
0x40, // 2082-03-29 to 2082-10-25
0x36, // 2083-03-28 to 2083-10-31
0x14, // 2084-03-26 to 2084-10-29
0x03, // 2085-03-25 to 2085-10-28
0x62, // 2086-03-31 to 2086-10-27
0x51, // 2087-03-30 to 2087-10-26
0x36, // 2088-03-28 to 2088-10-31
0x25, // 2089-03-27 to 2089-10-30
0x14, // 2090-03-26 to 2090-10-29
0x03, // 2091-03-25 to 2091-10-28
0x51, // 2092-03-30 to 2092-10-26
0x40, // 2093-03-29 to 2093-10-25
0x36, // 2094-03-28 to 2094-10-31
0x25, // 2095-03-27 to 2095-10-30
0x03, // 2096-03-25 to 2096-10-28
0x62, // 2097-03-31 to 2097-10-27
0x51, // 2098-03-30 to 2098-10-26
0x40, // 2099-03-29 to 2099-10-25
0x36, // 2100-03-28 to 2100-10-31
0x25, // 2101-03-27 to 2101-10-30
0x14, // 2102-03-26 to 2102-10-29
0x03, // 2103-03-25 to 2103-10-28
0x51, // 2104-03-30 to 2104-10-26
0x40, // 2105-03-29 to 2105-10-25
0x36, // 2106-03-28 to 2106-10-31
0x25, // 2107-03-27 to 2107-10-30
0x03, // 2108-03-25 to 2108-10-28
0x62, // 2109-03-31 to 2109-10-27
0x51, // 2110-03-30 to 2110-10-26
0x40, // 2111-03-29 to 2111-10-25
0x25, // 2112-03-27 to 2112-10-30
0x14, // 2113-03-26 to 2113-10-29
0x03, // 2114-03-25 to 2114-10-28
0x62, // 2115-03-31 to 2115-10-27
0x40, // 2116-03-29 to 2116-10-25
};

The row index is computed as (year - 2016). Each row is a BCD representation of intoDST and outFromDST dates, minus 25 (since the last Sunday always falls on 25th or later). So, 0x62 means on 31st (of March) we enter DST and on 27th (of October) we leave DST.

In order to avoid endless loop or complicated date jumps, the firmware will not change the time before 3 AM.

And this is the Perl script that produces the array above. It can be adapted to suit different DST rules, if a reader wants to follow my route.

#!/usr/bin/perl
use strict ;
use warnings ;
use DateTime ;

print "int DSTdays[100] = {\n";
for my $y( 2016..2116 ){

   my $ONdate = DateTime->last_day_of_month( year => $y ,
         month => 3 ) ;
   while ( $ONdate->dow != 7 ) {
      $ONdate = $ONdate->subtract( days => 1 ) ;
   }
   my $OFFdate = DateTime->last_day_of_month( year => $y ,
         month => 10 ) ;
   while ( $OFFdate->dow != 7 ) {
      $OFFdate = $OFFdate->subtract( days => 1 ) ;
   }
   my $ONymd = ($ONdate->day - 25) ;
   my $ONymdx = $ONdate->ymd ;
   #print "$ONymd;" ;
   my $OFFymd = $OFFdate->day - 25;
   my $OFFymdx = $OFFdate->ymd ;
   #print "$OFFymd\n" ;
   print "0x".$ONymd.$OFFymd.", // ".$ONymdx." to ".$OFFymdx."\n";
}
print "};\n";

Last but not least, this should be implemented in a clock firmware. And DST will be over in 4 days...

Cheating on DST calculation

My homemade clocks currently lack a commodity feature: automatic switch to daylight saving time and back. Throughout Europe this change occurs in the early hours of the last Sunday of March and October. I do have an RTC that can keep track of day-of-the week, but no clocks o' mine display it, so it is usually left out when setting date and time.
On the other hand I usually have lots of unused code/EEPROM space in my Arduinos, so I am seriously considering to hardcode a static table of the last Sunday of March and October. It is a lazy solution, but a change in the official DST rules would require a firmware update anyway.

Without carefully packing up data, I would need two bytes for each year, one byte per last-Sunday value. Something like:

int DSTdates[3][2] = {
   {27, 30}, // 2016, get it with DSTdates[currentYear-2016][0] and DSTdates[currentYear-2016][1]
   {26, 29}, // 2017
   {25, 28} // 2018
};
My usual Arduino sketch leaves way more than 1000 bytes free for variables. If I hardcoded DST changeover for 50 years, that would account for 100 bytes. I could even leave it like that, but let's discuss further optimizations.
DST for 2016 will be over in a week, that is more or less the amount of time it will take me to implement this function and update my clock firmwares around the house. Nevertheless, since we still live in 2016, I need to keep that line in the bidimensional array otherwise it would break the lookup algorithm that begins from 2016.
Second optimization. The last Sunday of March and October will always be on day 25 or later, so the array data can be rearranged substracting 25 from every number. That means the day range will be between 0 (= 25 - 25) and 6 (= 31 - 25). If we think of these numbers in BCD, they now fit in one single byte. In the previously allocated 100 bytes I can now store 100 years of DST changeover! This is how it looks now:

int DSTdates[3] = { 25, 14, 03 };  // 2016, 2017, 2018

While the code above is not human-readable, a simple lookup function does the trick. And since I will write a simple program to generate the array, I don't worry about those unreadable values as long as the unpack function works.

Now I need the script to generate the array. Stay tuned!

Olivetti Logos 262 PD expanson: calcuclock complete!

There you go! My first desk calculator conversion is complete!

I bought an Olivetti Logos 262 PD from 1980's, whose only guilt was to have a VFD display. I reverse-engineered the keyboard connection and designed a circuit to emulate keypresses with a microcontroller. Once the circuit has been built and tested, I wrote an Arduino firmware that reads an RTC (battery-backed clock) and types the numbers into the calculator. Last but not least, the clock circuitry can be disabled and the calculator used as originally intended.

Display modes are bonded to the way a calculator interacts with humans. Mode is changed towards the end of every full minute and includes:

• YYYYMMDD.HHMM
• HHMM.DDMMYYYY
• HHMM
• DDMMYYYY.HHMM
• HHMMSS
• HHMMSS.DDMMYY

The latter two modes are interactive in a way that the displayed information changes every second.

 One more thing needs to be implemented, both in hardware and software: a way to set time and date!

If you need inspiration, the firmware is on github. While I have lots of notes on scrap paper, I do not have a complete schematic diagram to share. If I locate another calculator to convert I will draw a diagram so that it can be reproduced.