The 'FotoStor MkI'

Forum for discussion of SSTV topics. Slow Scan television (SSTV) is a picture transmission method used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or colour.

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The 'FotoStor MkI'

Postby Steve Anderson » Wed Sep 29, 2021 4:35 pm

This in concept is very similar to Ralph Taggart's 'ROMscanner' device.

However, it's an update. The EPROM(s) have been replaced with larger capacity Flash Memory with the ability to program itself, not requiring chips to removed from the unit for an update or editing. The memory can be configured from a single 32Mb device to two 256Mb (32MB for a total of 64MB)

FotoStor Main 1.gif


From a SSTV perspective it stores frames at 128x128 pixels with an 8-bit video depth, i.e 16,384 bytes each. With a single 32Mb (4MB) memory that's 256 SSTV frames. With 2x128Mb (2x16MB=32MB) yields 2048 SSTV frames. Someone check my math!

For NBTV, following Ralph's arrangement, say twice that amount in NBTV video frames, around 5-6 minutes of video, less sound. A rough outline is above...

With the worldwide chip shortage I've tried to make this as flexible as possible r.e. memory chips. More anon...just looking at local suppliers and those in the UK, lead times are into mid-next year...ho hum...

Also all Flash memory runs at 3.3V, or at least the majority, so this will be a 3.3V device, not 5V.

Steve A.

My math is a bit wobbly, I'll come back to it later...

Before I go much further I need to think about the operator interface with this unit, frame selection via rotary switches and the like are out...
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Re: The 'FotoStor MkI'

Postby Steve Anderson » Wed Sep 29, 2021 7:08 pm

Actually why not do the SSTV output as PWM then filtered? No reason why not and easier, baseband SSTV then a FM modulator?...or both in parallel? More thought required...so many choices, so few chips...

There are a few/many other suppliers too, but I don't trust them, mainly of local origin to me, simply no-go for me...I'd rather pay twice the price and get something you know will meet specification...even if I have to wait...

I bought a dehumidifier to keep my printers happy. It worked, for two months, then crapped out. Guess where it was made? Really, do I need to say? Refund, replacement? Forget it....

Steve A.
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Re: The 'FotoStor MkI'

Postby Steve Anderson » Sat Oct 02, 2021 3:03 pm

I found this pretty little capacitive-sense keypad locally, outputs ASCII, binary or hex - ideal...OK on 3.3 or 5V. Even the manual unusually is in English (sort of)...not sure what I would do with the 'Help' key though...

If you decide to visit the suppliers website (URL in manual), be warned, it's 99% in the Thai language, currency too, with little to no English..

Originally I was thinking of an old phone keypad, except I don't have any old phones...

Steve A.

Manual Cap Keyboard 1.pdf
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Re: The 'FotoStor MkI'

Postby Steve Anderson » Sat Oct 02, 2021 3:58 pm

I'm sure most have seen something like this before...

-- Q U E S T I O N: Why do the numeric keypads on computers and calculators reverse the configuration on a telephone? I’m certain that thousands of wrong numbers are dialed daily because of this. — David K.

Q U E S T I O N: Why do the numbers on telephones go from 1 in the top left corner to 9 in the bottom right, while calculators and computer number pads go from 1 in the bottom left corner to 9 in the top right corner? — Joel K.

A N S W E R: A wonderful question, gentlemen, and something that I have puzzled over myself. After all, here are three devices that we use on a daily basis, and they all share a basic layout — an array of 10 numbers in a three-by-three arrangement with the zero sitting down below. Yet the numbers are reversed. So what gives? Why aren’t all such devices created equal, anyway?

Let’s first set the context. The time is the late 1950s. The place, Bell Laboratories, where researchers are preparing to introduce an alternative to the rotary telephone, something they called push-button dialing (which later came to be marketed as “Touch Tone” dialing). The question: how to arrange the numbers.

There were two logical models, of course. The existing rotary phone with its circular dial and counterclockwise number arrangement, with the 1 sitting in the upper right, was one. The calculator was the other. Back then, the industry-standard typical calculator had nine columns of numbers, with 10 numbers in a column, the lowest digits at the bottom, starting with 0 and moving up to 9, and was basically a mechanical adding machine that closely resembled a cash register.

One common explanation for the discrepancy between the phone and the calculator is that phone company engineers intentionally reversed the calculator layout because their research showed that people who were already adept at using a calculator punched the buttons too quickly for the telephone switching equipment to correctly register the numbers. But accounts from people who worked for Bell Labs at the time indicate that this version isn’t necessarily the case.

A Case Study

The real answer seems to lie in a study conducted at Bell Labs titled “Human Factor Engineering Studies of the Design and Use of Pushbutton Telephone Sets.” Published in the July 1960 issue of the Bell System Technical Journal, the report says that researchers tested a number different layouts including the three-by-three matrix with the zero at the bottom; versions with two rows of five numbers, arrayed either horizontally or vertically; and circular configurations with numbers laid out in clockwise and counterclockwise fashion. The study concluded that the three-by-three version with 1-2-3 in the top row was the easiest for people to master.

There was another reason as well. When it came time to match letters of the alphabet up with the numbers, putting 1-2-3 across the top made a lot more sense because it was the most natural way to get ABC in the top row. If 7-8-9 had been at the top, one of two things would have happened — the letters and the numbers would have run in opposite directions, or PRS would have been the first set of letters. Either arrangement would have seemed very odd, indeed.

All this raises another interesting question. When Bell Labs began exploring keypad layouts in the late 1950s they contacted all of the leading calculator manufacturers to find out why they had chosen to put low numbers at the bottom and high numbers at the top rather than the other way around. The answer, apparently, was a big shrug. It turns out that decision was largely arbitrary: no one had done any research about which layout was most convenient for users. Still, when it came time to place a numeric keypad on a computer keyboard, the calculator model with 7-8-9 at the top prevailed.

Todd Campbell is a writer and Internet consultant living in Seattle. The Answer Geek appears weekly, usually on Thursdays.


A bit of trivia for you! A lot of people are unaware of this until you mention it. Even the calculator keypad within your mobile phone is reversed to the dialing keypad!

Anyway, I digress, again!

Steve A.
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Re: The 'FotoStor MkI'

Postby Dave Moll » Sat Oct 02, 2021 7:02 pm

Steve Anderson wrote:The time is the late 1950s. The place, Bell Laboratories, where researchers are preparing to introduce an alternative to the rotary telephone, something they called push-button dialing (which later came to be marketed as “Touch Tone” dialing). The question: how to arrange the numbers.


As a further slight diression, push-button telephone dialling and "Touch Tone" (or more properly "MF" - multi-frequency dialling) are not entirely synonymous, as early push-button telephones (and some later ones as an option) produced strings of loop-disconnect pulses to simulate a rotary dial, thus enabling push-button telephones to be used on electro-mechanical exchanges.
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Re: The 'FotoStor MkI'

Postby Steve Anderson » Sat Oct 02, 2021 7:55 pm

Back to the FotoStor, initially it looks like I'm going to be using 2x32Mb Flash memories, as the larger ones are zero stock here. That's 64Mb, (8MB) in total, which for 16kB SSTV frames is a total of 512 SSTV pictures. When the 64Mb versions return that'll double to 1024. If using Ralph's 'ROMscanner' arrangement of 32x256 pixels, a total of 1024 or 2048 frames of NBTV respectively. Though if you paired that down to 32x128, a total of twice that amount, or even 32x64 (still OK), four times that, 4096 or 8128 frames....you could go on and on...

There are also 128Mb versions, but so far only from companies I've not seen or heard of before, e.g. 'Winbond'. I'll give 'em a miss thanks....

One of the issues is just because it's 64Mb (or whatever), depending on who makes it, the memory map, instruction set, and protection arrangements are often different. It's not like a 7400 is a 7400 is a 7400...whoever makes it. So I need to use something universally available, back to Microchip again...perhaps Atmel...but although twice the price per byte of these unknown companies, they'll work and not fail just because you looked at them. (Remember early CMOS? I do!)

The SSTV-VGA up-convertor is stalled as my old Tek 100MHz quad channel 'scope isn't up to the task. But for this it's fine...another investment, but it's needed for 'real work'. I might have to invest in a decent logic analyser too...I'm supposed to be retiring at my age...

Steve A.
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Re: The 'FotoStor MkI'

Postby Steve Anderson » Mon Oct 04, 2021 6:39 pm

Retiring or not, here I am! Conceptual sketch of 'Fotostor MkI' attached. Memory chips to be sorted out. The plan is that the micro will interrogate each whether present or not and their size/layout. To limit the number of variables the limit will be, 1 or 2 chips (if two, both must be the same), all sourced from Microchip, and each between 16Mb and 128Mb each (2MB to 16MB). This could/will be expanded in the future...start simple...then add...

There will be a requirement for some peripheral stuff added to this, but generally quite simple...

As things stand I can get all the chips I need for this now, or I already have them.

The 'jumper', JP101 could be a recessed switch needing something like a small screwdriver, ball-point pen or similar, just to make sure it doesn't get accidently moved.

Steve A.

Added a 'Sync Add' output on RC5 (pin 16) for the baseband NBTV and SSTV outputs. Not worth re-uploading the circuit again at this stage...

FotoStor Main 2.gif
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