Schmitt-trigger in oscillator , will it oscillate ?

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Guyzz

I need to make a simple simcard reader (fast), and this one is simple.

http://www.ladyada.net/make/simr...

They use a 74HC04N in the oscillator circuit , but i only have some 74ACT14 home.

Would a 74ACT14 oscillate ?

Here they use a schmitt-trigger in fig. 1a , and also have a citcuit much like the one above in fig. 1c
http://www.linear.com/pc/downloa...

/Bingo

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74ACT14 should work. Possibly adjustment of R1 up would be needed. Schmitt trigger has already some positive FB, the rest is the same as regular gates in series.

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Schmitt triggers are definitely not recommended for oscillator designs. It may work by heavily adjusting R1 (feedback resistance) to smaller, but that would load the crystal too much. Also the positive feedback on input also means more current is needed to overdrive the positive feedback.

Besides it is an ACT so it uses TTL compatible voltage levels, so the bias point for the input is definitely not half of the vcc.

I'd say best would be to use 74HCU04 than 74HC04 even.

Just put the crystal next to AVR and have it output the clock to the card.

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Just buffer the clock out from a small AVR

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@Jepael / Sparrow

I was afraid of that ...

I read several comments in the appnotes , where they mentioned "Low freq".

I have a LS04 , and might try a ttl oscillator , buffered with one of the ACT14 gates (at OUT).
http://www.eleccircuit.com/wp-co...

Meaning i'll use a LS04 for clock , and an ACT for the rest of the above circuit.

Will try it out asap.

/Bingo

Last Edited: Sat. May 14, 2011 - 12:14 PM
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Where in DK do you live, I have everything (if I can find it).

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sparrow2 wrote:
Where in DK do you live, I have everything (if I can find it).

Thanx Sparrow ... (CPH)

But i need the stuff monday.

Have 200 simcards i have to , discontinue @ TELENOR.

And no info on the cards , so i need the above simcard reader to read out sim serial , (expect to semicolon separated CSV).

Then i can ship that to TELENOR

/Bingo

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I have seen Schmitts work as oscillators, and once had an argument with someone I was working with who used one in a design (it did oscillate), but I'd use a 74HC04.

Leon Heller G1HSM

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Found a 74AC20 in the drawer ...
Used it as the 2 "Nor Gates" in the osc.

Seems like it works , the ringing might be the "breadboard" that it's currently build on.

/Bingo

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Why not just use an AVR to read out the sim's? If you have an Arduino [or any other development board with a serial port for that matter], shouldn't take you more than an hour or so to put something together to read the serials.

Oh, IIRC the protocol is ISO-7816. You send a reset, and it sends back an "Answer to Reset" within 40,000 clocks. The ATR defines the rate for any communications going forward. the initial clock divider used for the baud rate is 372. The default communications rate is around 9600baud when clocked at 3.571MHz. [note this applies to asynchronous cards only, which I believe sim's are]

Writing code is like having sex.... make one little mistake, and you're supporting it for life.