Light work for new input pen

IN YOUR REVIEW of the dK'tronics light pen, to say that the suggested delay routine causes an immediate crash on the 48K Spectrum is a damaging comment and untrue.

Although I have no connection whatever with the company - I am just a well-satisfied customer - I feel compelled to tell you that I have found no difficulty with the delay and to denigrate the excellent device, however slightly, through what must surely have been an error on the part of your reviewer, is unfair.

The delay routine suggested can prove very useful but it is not obligatory. I have written a program for family use which gives two hours' amusement without having to use the Spectrum keyboard, except to enter the number wishing to play, and their names for the scorecards, after loading.

That worked perfectly with the delay routine which your reviewer condemned but I have now abandoned it to speed the action and add another competitive aspect to the game options, all of which, and there are many, are selected by pointing the pen at the appropriate areas on the screen.

Incidentally, I have not written this to sell my program. My efforts in that direction are strictly for home consumption and my own amazement.

I thought it only fair to say that the dK'tronics light pen has added very considerably to the pleasure I derive from my Spectrum and I hope that you will review your review.

Alfred Bone

Dolphin camp confusion

I WRITE with regard to an article in your June edition in which you talk of the holidays organised by Dolphin Activities Ltd as being Dolphin Camps. You will notice that Dolphin Activities Ltd does not use the term Dolphin Camps because that name is applied to some camps which we have organised since 1919.

The Dolphin Camps are canvas camps organised for preparatory schoolboys on the cliff-top at West Runton, Norfolk. In addition, for older children, we organise specialist camps for go-karting, canoeing, sailing.

You will appreciate that the similar names tend to cause some confusion which we are anxious to avoid.

N Taylor

Cheaper file solution

I WAS READING Sinclair User Hardware World May edition - when I saw the article for an improved printer spool.

I believe that I have a much cheaper method of dealing with the problem. A folded piece of printer paper is inserted in the slits in the side of the plastic ends and then wrapped around.

When the end is pushed into the roll of paper it fits much more tightly and seems to eliminate the problem.

Nicholas Atkinson

Unsolicited compliment

MAY I comment on the quality of your magazine? It has improved month by month and I find it an excellent mixture of reviews, comment, news items and advertisements. I look forward to receiving each new edition with increasing interest.

David Brown

Simple binary conversion

I HAVE FOUND that among my friends who own Spectrums and also note from many of the programs you publish that many people have difficulty in transposing binary numbers as used in graphics into decimal.

The eight digits can each be allocated a number, thus:

If any of the eight digits is expressed as a '1' in the binary number, the number below that digit is taken as the decimal. If more than one box is expressed as a '1', the sum total is the decimal:

Take the decimal numbers below the '1's which in this example are 64, 16, 8 & 1 and add them together = 89.

B Dickenson

Lower cost of planned cycle

THANK YOU for your review in the July issue. I wrote to you to inform you that we had reduced the price of Cycle Planner/Growth Tracker from £7.25 to £4.95. Unfortunately that was not conveyed in the review which had as one of its criticisms the cost of the cassette.

We had two quarter-page advertisements in Sinclair User May/June - and have refunded £2.30 to all mail order customers after May 25.

Medidata

Plea for more machine code

HAVING RECENTLY bought a Spectrum, I have restarted the quest for machine code programming, having already broken through on the ZX-81. I can say now that I am fairly proficient at it but I wish to make a complaint.

You have not yet in any Sinclair User issue made more than a passing reference to Spectrum MC and little more in the case of the '81. Machine code programming is not really so difficult if you try and it is most satisfying. I am sure it would become much more commonplace if you printed articles on MC programming techniques and advice, and fewer articles in the vein of User of the Month and fewer large, spacious illustrations and pictures.

Further, what about giving Andrew Hewson more pages? He is often helpful and is to be encouraged.

Finally, I am glad to see that you often review current software, as an unbiased opinion is often a good guideline on a certain tape. In the one tape I have bought which you had reviewed, however, I was misled by you. The game, Winged Avenger by Work Force was, you said, difficult. That is rubbish. When my sister, aged 11, and I play it, the only limiting factor to a high score is how many hours we have to spare to play. It is undoubtedly the worst Spectrum game I have seen, so please review games critically.

J H Fletcher

We are looking at a series on machine code programming on the Spectrum but will not be printing it at the expense of more general articles, such as User of the Month. Our readers have a wide range of interests and we shall attempt to continue to cater for all of them.

While one person's criticism is another's flattery, we always try to give readers a good idea of what to expect from the software on the market and will not be afraid to make critical remarks where they appear justified.

Keeping faith with Sinclair

I HAVE been reading Sinclair User for about five months and find it very good value, but I have had difficulty with Sinclair computers in the past.

I had two 81s which were faulty and then I got fed up with the two 81s and brought a TRS-80. It had no colour graphics so I bought a Spectrum, which I have had for a month and find it a very big improvement on the ZX-81. Keep up the good work.

R Cordes

Randomized screech

WHILE I was experimenting with the command RANDOMIZER USR on my 16K Spectrum I discovered that by typing-in RAND USR 1331 a magenta and blue-striped border was produced and a screeching sound was emitted from the computer. That can be stopped by pressing SPACE.

That strange bug, if it can be called that, can easily be accommodated in games, as it apparently has no effect on a program.

Does anyone know why it does it or how it does it? Also does anyone know a method of getting rid of the aggravating Spectrum buzz?

I would like to conclude by pointing out a bug in Andrew Hewson's decimal loader on page 102 of the June Sinclair User. Surely line 60 should read GO TO 20 or the numbers are poked into the same address each time?

Aidan Taylor

Portable computers

IF ANY READERS are looking for a cheap, strong carrying case for a small computer, could I recommend the Gear Box from British Home Stores? It is a strong plastic lunch box 36x28x12cm. and holds my Spectrum, all leads, a small tape recorder and a few tapes and books. I have lined it with thin foam. It does the job well and costs only £4.50.

Many thanks for an excellent magazine. My only complaint is what happened to the regular education slot?

Elizabeth Atherton

Disc limits warning

I BOUGHT a copy of Pete Shelley's cassette XL 1. I had problems loading the cassette into my Spectrum, so returned the cassette to the record shop, which exchanged it for another copy. That copy would not load.

I telephoned the record company, which told me that the cassette is only for the 48K Spectrum. Nowhere on the cassette or the packaging did it say so. I would like to warn other 16K Spectrum owners to prevent them buying the cassette hoping to load it into 16K Spectrums.

Bryan Griffiths

Extra resistor causes problems

LIKE ALL apparently simple solutions to the problem of ZX-81 over-heating, W D Langton's ideas of a 5ohm resistor in the power supply lead is likely to lead to additional problems which could be even worse than over-heating.

My ZX-81 with 16K memory draws, on average, 700ma and when the printer is working at full stretch it rises to 1,100ma. Now 700ma will cause a voltage drop of 3.5V, and 1,100ma a drop of 5.5V across the 5ohm resistor. That means that the original 10.5V - 10.75V on my Sinclair power pack - will drop to either 7.25V, or 5.25V if the printer is 'flat out'.

In addition, the value of the smoothing capacitors on the Sinclair power supply means that a ripple voltage of 2.2V at 700ma, and 3.4V at 1,100ma, is present. When the ripple voltage is subtracted from the voltage with the 5ohm resistor in circuit, it does not take much imagination to realise what can happen, as the ICs in the ZX-81 require a 5V supply. Hence the reason for the 5V regulator in the ZX-81.

There is a minimum voltage drop across the regulator which will not work properly unless the voltage to the regulator is at least 7V.

Practical consequences can be white-outs, crashes, printer malfunction - just name it, you have it.

The only really satisfactory solution is a regulated power supply of about 7.5V, which will cure all problems.

If a simple compromise 'cure' is sought, it is well worthwhile inserting four silicon rectifier diodes of 2amp rating into the supply lead instead of the suggested resistor; doing so will give a voltage drop of about 2V irrespective of the current drawn by the ZX-81, which is not the case should a resistor be used.

Another improvement would be to increase the value of the smoothing capacitors by 2000MFD. The ripple voltage on the supply line would then, at worst, be 2V instead of 3AV.

Although not perfect, the result would be that the ZX81 ran much cooler and any other problems would not be precipitated, or made any worse than before the modifications.

Charles Rowbotham

Is this a new record?

I HAVE just saved Bill the Worm from the ninth level in Mined Out for the 48K Spectrum. My score was 7,400; is that a record?

I have also scored 82,812 on the Silver Soft Cyber Rats and 153,350 on Artic 1 Galaxians. Why not print a league table of high scores every month?

Graham Lawrence

Expanding factorials

THERE ARE various programs for calculating permutations and combinations. They always have limitations because they necessitate, somehow or other, calculating the factorials of various numbers; the factorial of a number, of course, being 1x2x3x4 ... up to and including the number. Calculated that way, the biggest factorial which can be computed on a Spectrum is 34.

With a little improvisation, the range can be extended considerably, by using the logarithm key:

5 REM LARGE FACTORIALS
10 PRINT "FACTORIAL NEEDED?" INPUT X: PRINT X
20 LET A=LN 1 
30 FOR B=1 TO X
40 LET C=LN B
50 LET A=A+C
60 NEXT B
70 LET D=A/LN 10
80 LET E=D-INT D
90 PRINT "FACTORIAL OF X;X;" IS ";
10[to the power of]E;
"TIMES TEN TO THE POWER"; INT D

I have not discovered the limits of the program. I have established that the factorial of 2,000 is 3.3163794 times 10 to the power 5735. It must be said that my Spectrum is a little costive in yielding results at this level and patience is called for.

Rev H S Corran

Large demand at low price

IN THE JULY ISSUE, Early end for the ZX-81? you write that in your opinion there is probably a base price for computers of about £30 and also that a fall in prices would mean the early end of sales of the ZX-81.

In my school, and I am sure the same could be said for most schools, the only opportunity many children have for devising their programs is when they have the chance of time with one of the school machines. They would dearly love to have their own machines but their parents cannot afford the £40 for even a ZX-81.

If the basic price of a ZX81 fell to £30 or even lower, many parents would not only be able but also keener to buy. If a child did not sustain interest, the amount spent would not be too great. If interest was sustained it would be money well spent. Further opportunities birthdays and Christmas would provide extras or even a trade-in for something better.

D Gilbert

Club call in Tameside

I WOULD like to start a Sinclair computer club in the Tameside, Lancs area but first need to find if sufficient people would be interested.

Jacqueline Wright

Making notes while listing

THERE ARE two small improvements I think you could make to Sinclair User - the addition of small notes under the program listings illustrating how programs can be converted from the Spectrum to the ZX-81 or vice versa; and how about reviewing the software produced by smaller firms such as the ones which advertise in the Supermart.

Apart from that, does anybody know of a Basic statement which will read what is typed-in and give X that value, replacing the lengthy "IF INKEYS="2" THEN LET X="2" statements?

Alistair Hodgett (13)

Thank you for your tips, which we are considering. In our reviews we make no distinction between large and small companies. Because most companies advertising in Supermart tend to be small, new producers, there is not always time to review their products at the time they advertise.