An improved calendar?

Updated 28 Feb.

Following my last post, here is one suggestion for a new calendar, having a different number of days for 8 of the months in the year (highlighted). The current number of days per month is in the second column, the proposed number is in the third, the difference is in the fourth and the accumulated difference is in the fifth, which we'd expect to vary over the year, but to be 0 by the end, as indeed it is!

January	31	30	-1	-1
February	28	29	+1	0
March	31	30	-1	-1
April	30	31	+1	0
May	31	31	0	0
June	30	31	+1	+1
July	31	31	0	+1
August	31	31	0	+1
September	30	31	+1	+2
October	31	30	-1	+1
November	30	30	0	+1
December	31	30	-1	0

Let's see what difference this makes to the dates for equinoxes and solstices: 

• first, we'll fix the 2025 Autumn Equinox at Sep 22 (i.e. unchanged)
• the 2025 Winter Solstice is also unchanged on Dec 21, as there are still 91 days in total in the three months of September, October, November
• the 2026 Spring Equinox, almost exactly 89 days later is now on Mar 21, one day later in the calendar than now, as there are now 89 days in the three months December, January and February, as opposed to the actual 90
• the 2026 Summer Solstice, nearly 93 days later is also unchanged on Jun 21, as the number of days in total in March, April and May is still 92
• the 2026 Autumn Equinox, again nearly 93 days later is now on Sep 22, one day earlier in the calendar than now, as the number of days in total in June, July and August is now 93, rather than 92.

So, we can see that with the new equinox dates there would be less variation in these day numbers than before, i.e. on the 21st or 22nd of the month, as opposed to the 20th to 23rd (at least for the years quoted).

If there is a leap year, then we could give the extra day to February, as now, to make it a "proper" month with 30 days, so the number of days in any month would now only ever be 29, 30 or 31.

One final point - why not make December the shortest month, at 29 days and 30 in a leap year? Well, think of the potential for confusion, e.g. do we celebrate New Years Eve on the 29th or is there a 30th this year? January then? Well, it's so close to February, so let's stick with tradition.

The diminution of February

Updated 28 Feb.

My other half was pondering recently as to why February has so few days compared with the other months and with its immediate neighbours in particular. I responded that the Earth's orbit is not circular and during Winter, the Earth is a little closer to the Sun and moves more quickly, so something has to give at that time of year. Perhaps for some reason, it was decided that January and March were too important to give up any days, but February could take the hit instead and in a big way.

Anyway, I decided to look at the numbers. The dates and times (GMT) of recent and future equinoxes and solstices is as follows, with the last column being the time between the last event and current event (by my reckoning)*.

Autumn Equinox ‘25	22 Sep	18.19	-
Winter Solstice  ‘25	21 Dec	15.03	89 d, 20 h, 44 m
Spring Equinox  ‘26	20 Mar	14.46	88 d, 23 h, 43 m
Summer Solstice ‘26	21 Jun	08.24	92 d, 17 h, 38 m
Autumn Equinox ‘26	23 Sep	00.06	93 d, 15 h, 22 m

Those 'deltas' confirm the point I made and that it would make sense to have longer months in the Summer (by which I mean between the Spring and Autumn equinoxes), of generally 31 days, and shorter ones in Winter (by which I mean between the Autumn and Spring equinoxes), of generally 30 days, suitably adjusted to ensure 365 days per year and 366 in a leap year, of course. It should also mean less variation in the day number of the equinoxes and solstices.

(*Also by my reckoning, totalling those deltas makes about 365 and one quarter days, as we should expect).

Pumped Storage

Originally posted on the RetroMat website a few years' ago, but is better placed here.

An often-heard criticism of reliance upon sources of renewable energy - specifically solar and wind power - is that they're no use when the sun isn't shining or the wind isn't blowing. This is not a trivial point - here in the UK, we do get such days nationwide, particularly in the winter.

Pumped storage schemes, whereby water is pumped from a lower reservoir to a higher one during periods of low demand and then released to flow back down and generate energy during periods of high demand, may look like a possible, if partial, solution. One such scheme is the Dinorwig power station in North Wales. (Another, 3 times the size, at Coire Glas in Scotland was proposed in 2013 and as at Feb 2026, is still proposed rather than under construction). The classic scenario for which it was intended is at the end of or during the commercial breaks of popular TV programmes when there is a rush to put electric kettles on to make cups of tea or coffee, i.e. to meet short bursts of high demand. However, it  can hold around 9 GWh of energy, enough for the daily requirements of about 1 million households, so can also be used for short-term storage. 

I read a while ago about a proposal to install such a system on a small scale in a high rise tower and this led me to wonder - briefly -  if it might be a practical solution for use in (2-storey) homes here in the UK, where traditionally we have had cold water storage tanks in the loft. There's been a move away from these in recent years with tanks being removed when combi boilers are installed. What if these were left in place and adapted for pumped storage instead? Could they be of use, even if drawn on for brief periods only?

Let's assume such a tank can hold 200 litres of water and is 5 metres above ground level. The potential energy stored in the tank is the weight of the water (200 kg)  times the acceleration due to gravity (~ 10 metres/second/second) times the height of the water (5 m), i.e. 10k Joules. That's 1 kW for 10 seconds, so 1/360 kWh, barely enough to power a low energy bedside light for 40 minutes! By contrast, batteries provided with domestic solar power systems typically store several kWhs. 

Not surprisingly, it's a fraction of the energy needed to boil water for a cup or two of tea, say a half litre of water. To boil this amount from room temperature (perhaps 20 degrees C ) requires the mass of the water, 0.5 kg, times the Specific Heat Capacity of water, 4200 J/kg/degree C, times 80 degrees, i.e. 168k Joules. That's only around one 1/20 kWh, but is still about 17 times the potential energy stored in the cold water tank!

So, it's a non-starter for our 2-storey home.  What about high-rise accommodation? Let's consider that water tank 100 metres up. In this case, it would store 20 times the potential energy, 200k Joules, enough to power that light for a little over half a day, and also now to boil that kettle! To provide that energy for all the households in the building, there would need to be a lot of water stored at the top, however.  Just think of the extra weight and the need to support it. Even if feasible,  managing peak demand through pricing would surely be a more effective solution. 

And anyone thinking that the problem of balancing supply and demand could be solved by simply building more pumped storage schemes should consider this:  in the UK we would need the equivalent of around 30 Dinorwig  power stations to store just 1 day's worth of electrical energy for domestic consumption alone and that's before considering any losses due to conversion, transmission and plant outages.

Back to those batteries used with domestic solar power:  those could keep an average home going for just a few hours - very useful in times of occasional power cuts of short duration, but much less so during a prolonged shortage of energy-generating capacity. EV batteries on the other hand can store 10s of kWhs of energy, enough for a household for several days of outages. It's an interesting idea to use these to back up domestic supply, even if it does mean people not being able to use their cars as a result. 

However, EVs are still very expensive to buy (even if much less so to run than petrol or diesel ones) and if we want to keep the lights on for everyone, then for the foreseeable future we'll continue to need to have substantial backup generating capacity in the form of gas turbines which can be switched on and off readily (unlike nuclear power stations). 

And here's a video on YouTube from someone who seems to know what he's talking about who's of a similar opinion, although I tend to think of wishful thinking/delusion/over optimism rather than hoax here. 

Unfortunately, there is a disastrous lack of critical thinking going on with energy policy when the climate zealots are in charge, as they are here in the UK. In particular, the "exporting" of our manufacturing industry sector and of our carbon footprint in the drive to so-called "net-zero", an accounting sleight-of-hand that will have no impact globally and a very damaging one here.

A home-built 4-bit TRANSISTOR computer

Here's another terrific home-built computer project, but this time a 4-bit one using transistors - over 960 of them! It holds just 10 bytes of memory - just over half that of Ben Eater's SAP-1. I wonder what can be done with that?

Plugboard Programming

I've just come across this wonderful item about hard-wired programs on a tabulating machine  - the IBM 403 Accounting Machine, released in 1948.

It was news to me that the plugboards were removable, so that programs could be retained and reused as required - that picture of shelves of wired plugboards is going to stick in my memory!

Perhaps this could serve as inspiration for programming the simple transistor-based computer I've been mulling over? I'd already thought about doing something similar to store the sequences of notes used for an analogue synthesizer.

A (constrained) home-built 8-bit computer

Updated 21 Feb 26

It's this one, of course, by YouTuber Ben Eater. It's IC-based, with not a transistor in sight. I've had a good look at some of his excellent videos, in particular the ones about the registers, the ALU (AU really) and CPU control logic. He even gets to write his own operation codes, micro instructions and assembly language!

His computer is based on one of the machines (the SAP-1) in the book Digital Computer Electronics by Albert Paul Malvino. It has a proper computer architecture and seems very much designed from the top down, whereas I was thinking of moving in the opposite direction, from the arithmetic unit (see a previous post).

It's intended to demonstrate how computers work - the machine can be stepped through instructions one clock cycle at a time and there are LEDs to show the contents of stores. Even so, it's severely limited by having just 16 bytes of program memory! I wonder why it was designed like this? Even with 64 bytes (lines), say, you would be able to write some interesting programs, as I did with a Diehl programmable calculator of similar capacity over 50 years ago. I can only assume it would not be easy to expand it, otherwise surely it would have been done? (The next computer in the book, the SAP-2, can address up to 64k Bytes of memory). 

I suppose much more capacity for storing programs would highlight how tricky it is to program with those small dip switches, so larger ones would be needed. A punched paper tape machine and reader would be very useful, if unlikely, additions, but in the absence of those, I think a modern means of programming the EEPROM is quite permissible, as indeed the builder shows with an Arduino. And a ROM with routines for multiplication and division and handling of decimal numbers would be cool, too. 

The following notes are here really for my own benefit.

Some key features/highlights:

• an arithmetic unit (AU) supporting addition and subtraction
• two registers, A and B, the contents of which are automatically added into the AU
• registers and other stores can receive (load) and send (enable) contents
• communication between pairs of stores is via an 8-bit bus, one store in send mode, one store in receive mode - no need for point-to-point wiring, hence expandable
• use of tri-state (0, 1, disconnected) gates to control which stores can send (and receive?) data at a time
• 16 bytes* for program storage (in EEPROM), each byte comprising:
• a program line: 4 bits for instruction, 4 bits for associated data
• a data/variables, typically after lines of code: 4 bits
• programming via dip switches (for memory location and content)

*limited by the use of a 4 bit Memory Address Register.

Program instructions

The machine in the book provides the following operations:

• ADD
• HALT
• LDA (load A register)
• SUB                        
• OUT (send contents of A register to output on 3 digit decimal display)

The builder adds these:

• JC (conditional jump) 
• JMP (jump)
• LDI ("load immediate")
• STA ("store accumulator")

These are each implemented by several steps of micro instructions, stored (semi-permanently) in EEPROM:

• AI (A register in)
• AO (A register out)
• BI (B register in; there seems to be no corresponding B register out)
• CE (program counter enable - increments counter)
• CO (program counter out)
• EO (AU sum/sigma out)
• HLT (halt)
• II (instruction register in)
• IO (instruction register out - lower 4 data bits only)
• J (jump)
• MI (memory address register in)
• OI ?
• RI (ram in)
• RO (ram out)
• SU (subtract signal?)

Note that most of these micro instructions simply send data from the output of one store to the input of another, i.e. they act as virtual wires. In fact, before building the control logic, Ben Eater demonstrates here exactly what is required of it by making direct connections between the relevant input and output gates:

Each instruction is first fetched into the instruction register by the following micro instructions:

• CO MI (puts the program counter into the memory address register)
• RO II CE (puts the instruction into the instruction register and increments the program counter)

Simple worked example provided by the builder:

This program adds two numbers, stored in RAM, together. 

Here are the micro instructions, in two steps, for the operation LDA 14 (load contents of memory location 14 into the A register):

• IO MI (loads data portion (lower 4 bits) of the instruction (14) into the Memory Address Register)
• RO AI (sends data at this memory location to the A register, from where it is automatically added to the AU)

If memory location 14 holds the number 28, then the A register and AU both contain 28.

Then ADD 15 (add the contents of memory location 15 to the AU, after being fetched), comprises the following micro instructions:

• IO MI (loads data portion (lower 4 bits) of the instruction (15) into memory address register)
• RO BI (sends data at this memory location to the B register, from where it is automatically added to the AU)*
• EO AI (sends data from the AU to the A register).**

*If memory location 15 holds the number 14, then the B register contains 14 and AU 42, ie. it has added the contents of the registers together. The rest of the code copies that data to output for decimal display.

** The A register now contains 42 and that number will also be added to the AU, but that is ignored here

Then OUT, to display the output, after being fetched:

• AO OI

It may seem that's a lot of steps to achieve fairly little - after all just entering the required data directly to registers A and B would have resulted in the AU displaying the answer, albeit in binary, automatically. That said, the author also provides a program to multiply two numbers and another to generate Fibonacci numbers. These and a couple of others can be seen here, for example.

(The Fibonacci one could be done in hardware alone by connecting the output of the AU to the input of the A register, i.e. equivalent to micro instruction EO AI, entering the number 1 into the A register and then starting the clock. We'd just need to make sure that automatic updating of the AU by the A register is disabled while AU itself updates the A register).

More thoughts on a "Computer Demonstration Model"

Updated 18 Feb 26

Recently I took another look at the book Computer Models, by A. Wilkinson, published in 1968 and mentioned towards the end of this item on my RM website. On page 107, in a section titled Suggestions for Further Development, the author notes the limitations of his model, which is essentially a very simple calculator, and says a programme of instructions to be arranged and carried out ... is essential if the model is to do a complete programming job. 

Indeed and this makes me wonder what the simplest programmable transistor-based computer would comprise? What instruction set would it need? The author's machine can already be told to add and subtract. There is a shift register operation too under the covers, so let's make that available. A compare instruction for logic, is needed of course. And ones to move data (numbers) between storage areas. No doubt others too - a look at the Diehl calculators is needed.

Let's number those instructions. The simplest form of programming would be a sequence of individual steps on a sheet of paper for an operator to carry out, each comprising an instruction number (selected by a rotary switch perhaps) and a piece of data, according to an agreed syntax, followed by the operator pressing a button to run that step. To use logic (repeated addition for a multiplication program, say), the operator would need to jump to another location on the sheet. By default we could put, say, '+1' at the end of each instruction to tell the operator to move to the next step. If we need to jump, then it would be plus or minus some other number.

Or write the program on a punched card, pushed into a reader, either by the operator or automatically (I'm thinking of Computacar from ~1970!) one low-level instruction step at a time. This reader could be opto-electronic or electro-mechanical. Handling jump instructions would be tricky though.

This could be a very interesting project!

Solar Spring

By my reckoning, in the small hours this morning we reached the halfway point between the Winter solstice and the Vernal equinox, so by this measurement it is Springtime. It also seems like Spring today with sunshine and birdsong!

The Gaelic peoples called this time Imbolc, which these days is celebrated on Feb 1st, a little too soon.

Feb 2nd was Groundhog Day, obviously related, in the US and Canada.

Then there's the Christian Candlemas, also celebrated on Feb 2nd, timed no doubt to replace any pagan festivities.

I find it surprising that the old Germanic and Nordic peoples don't seem to have marked or celebrated this time. Could it be perhaps because they only recognised the seasons of Winter and Summer, the latter starting in May?

Practical Wireless mini-two transistor radio

This project appears in a nicely-presented article starting on page 332 of the September 1969 edition of Practical Wireless Magazine. I first came across it, perhaps during a wet break, in the school library during my first term at secondary school in that month and year. I recall reading and re-reading the article with fascination - a real working miniature radio that I could build all by myself!

No doubt the inspiration came from commercially-available micro radios of the time, such as this one, claiming to be the world's smallest radio, from Sinclair Radionics. I suspect the makers of these radios wanted to give the impression that they were miniaturized fully-functional radios rather than the minimalist ones in very small packages that they actually were.

To make the most of the two transistors in the mini-two, the designer eschewed reflexing in favour of regeneration (a limited amount, according to the author), using a so-called gimmick capacitor consisting of a pair of insulated wires twisted together. Since this was inside the case, it would have meant taking the cover off in order to optimize reception for each newly-tuned station!

A complete lack of technical know-how on my part didn't stop me from buying the components, including the hairgrips box (the contents of which may be of use to our longer haired friends, as the author put it) for the container, and obtaining a soldering iron from a friend who was also intrigued by the radio. However, the project had a long gestation and I didn't get around to building it until the mid-1970s. Even then, I didn't bother with the case and tuning knob!

As far as I recall, after all those years of anticipation, I was disappointed to discover that I could only pick up one station with it and only that after wandering around the house trying to get a signal, fiddling with the controls as I went. Sadly it was put to one side before being discarded some time later during a clear-out. Perhaps if I'd persevered, I'd have got more out of it. On reflection, it seems pretty impressive that it could receive any station without an external aerial. 

Fast-forward to a few years ago and I was curious to compare its performance with some other minimalist radios I've been playing with, notably this one that uses a Darlington Pair transistor so I attempted to re-create it. Getting hold of the specified transistors was no problem. To save time, but deviating from the design, I opted to use the the coil and tuning capacitor in a Maxitronix crystal radio and connected that to a breadboard containing the required components, using the small winding of the coil to take the signal to the circuit.  I used two slightly depleted 9 volt batteries for power, giving around the required 15 volts. I dispensed with the gimmick capacitor and instead used a 25 pF trimmer, no longer being interested in the miniature aspect of this radio.

It did pick up BBC Radio 5 Live, possibly Talk Sport, and others at night, but in order to do so, it had to have an aerial connected to the larger coil, no doubt because there are far fewer MW stations around these days, so we can no longer rely upon the presence of powerful nearby transmitters. It was somewhat fiddly to tune, reception was dependent on the position of the aerial and some regeneration was always needed. Volume was acceptable, but there was some background whistling. My perception of it was less favourable than the Darlington Pair radio and the single-transistor-with-reflexing-and-regeneration version of the Ladybird radio. Sadly, my evaluation was cut short when the crystal earpiece I had been using was dropped and rendered unusable!

Overall, I'd say that while the radio has an interesting design, it's really a curio of limited usability. As for being an ideal project for the beginner, regrettably, I have to disagree with the author - as a newbie, after all that hard work, the last thing you want is disappointment! Perhaps the series of articles in PW entitled Simple Receivers for Beginners beginning in June 1968 would have been a better starting point?