Mystery Component

IIRC the crystal was 3MHz, I assume they'd run the MOS shift registers as fast as they could get away with - and that would probably be what set the upper limit.

One shift register recirculated the product of calculations past a row of TTL 7475s which latched the "correct answer" every time it whizzed past.

I think the BCD to Nixie decoder/drivers were also TTL, the bulk of the chips (over 200) were DTL.

On a sunny day (Fri, 1 Feb 2013 18:40:50 -0000) it happened "Ian Field" wrote in :

In the late sixties or maybe very early seventies I build a frequency counter with 4790 decade counters, and 7475 latches, cannot remember the number of the nixie driver chips, also TTL. It had a 100 kHz crystal as reference, 5 digits, counted up to about 30 MHz, as that was the maximum where the TTL would still work.

This is a fairly common term for a composite device... it's packaged like an ordinary transistor (SMT or TO-92), but includes a current-limiting resistor in the base lead (and often a base-to- emitter pulldown).

It's used as a power-switching device, driven directly from a logic signal (often a microcontroller pin).

Think of it as "just about the simplest sort of 'integrated circuit' you can imagine". It's even simpler than the tiny little "simple glue logic" chips you can buy these days (e.g. a NOT gate in a four-pin SMT package, or a NAND in a 5-pin).

On a sunny day (Fri, 1 Feb 2013 11:13:45 -0800) it happened snipped-for-privacy@radagast.org (Dave Platt) wrote in :

For a very short moment I did think 'unijunction transistor', at least those are either on or off, but then I dismiossed that on context. I bought a bunch of 2n4246 UJTs last year from ebay. Make nice oscillators.

The Nixie drivers in the calculators might have been 8T series - but its a long time to remember obscure details like that!

Also called "pre-biased transistors" or "resistor-equipped transistors" (RETs).

does B-E look like a diode or a diode plus some resistors.

have a look at some datasheets, they'e just odinary transistors with a resistor network on base and emitter (or a single resistor on the base)

Best regards, Spehro Pefhany

When I was a kid RTL became very available in surplus surface-mount packages (called "flat pack"). Probably some big military change-over. DTL didn't seem to last long.

Spacing was tight for attaching fly wires.. looks like it was relatively coarse by today's standards- maybe 1.27mm pitch like today's SOICs.

Best regards, Spehro Pefhany

On a sunny day (Sat, 02 Feb 2013 05:25:57 -0500) it happened Spehro Pefhany wrote in :

You could get cheap DTLand TTL chips here sold as 'bipack'. Those were for example 7474 D flip flops with one defective flip flop in the package, or a 7400 with one or more gates defective. Once bought some of those, tested them, and marked the defective pins with red marker. Great for hobby projects :-) Not so good if you made a PCB I guess :-)

mm I have wire wrapped several designs with TTL.

package,

Hey I remember those, in UK you could get bags (literally) of 7400 and

I remember that one - when I worked at the calculator repair firm, the chip they used became temporarily unavailable.

After canibalising all the scrap boards we were pretty much scuppered - for some reason it wasn't practical to patch the 74141 in.

The (old) Peak Atlas reports 2 diodes if it can't find any gain.

Poly-Paks was THE place in the US to buy them. I bent the pins for any bad section, and used lots of them to either build or repair equipment that didn't need that section.

Poly-Paks also sold some parts by the pound. It was a good way for a kid to get an assortment of resistors, caps sockets & such cheap enough to learn electronics. Do you have any idea how many resistors were in a five pound box? :)

Unless, of course, you count DTL redux (LSTTL). ;-)

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Wonderful example of something inexpensive now that would be difficult and expensive 25 years ago.

?-)

There was a hobby magazine project published somewhere at least 2 decades ago, similar type of thing as the DCA55 - it was pretty much someone thinking up something impressive to do with a HD44780 LCD module.

IIRC it was mostly SSI/MSI - unfortunately I can't remember what magazine it was, or whether a PIC based version was ever released into the public domain.