Comment on this Circuit

[akg]

Hi all..
some threads below . 'audio' has posted a ckt of RF Tx using logic chips
now i think this ckt is really ingenious in the design.. using chip that is never intended to use like that...
what do u think ? ....

 

[audioguru]

I don't think a crystal mic has enough current to force the input of an LsTTL gate low.
I don't think a Schmitt trigger inverter will oscillate with its input directly connected to its output.
Maybe miracles happen.

 

[akg]

I don't think a crystal mic has enough current to force the input of an LsTTL gate low.
I don't think a Schmitt trigger inverter will oscillate with its input directly connected to its output.
Maybe miracles happen.

i was also confused by the usage of schmitt triggered ttl , but his website says "it works" .. :roll: ... hmmm..
visit **broken link removed**

 

[audioguru]

his website says "it works" .. :roll: ... hmmm..

Watch out for circuits on the web. Maybe his wire from the output of the Schmitt trigger inverter to the input had resistance. Then it would oscillate.

I spotted one of his FM transmitters with its preamp transistor incorrectly biased. Maybe he connected it with its collector and emitter wires reversed by mistake, then the transistor's current gain would be low and the transistor would work.

 

[Roff]

I'm betting it works.
Anybody have a 74LS13? 74LS132?

 

[audioguru]

I guess the output of a 74LS13 must have some output resistance that would allow it to oscillate. Right?

 

[Roff]

I guess the output of a 74LS13 must have some output resistance that would allow it to oscillate. Right?

And propagation delay. Note the tuning capacitor on the output which uses the output resistance to create variable delay, and hence variable frequency.

 

[akg]

Maybe miracles happen.

as far as i know.. electronics is a science.. so is there any chance for miracles ?? if it works then there should be some reason .. the best thing would be to test it..does any one has the ic , and a 5min to spare?? . (i have time but no ic :wink: )

 

[eblc1388]

as far as i know.. electronics is a science.. so is there any chance for miracles ??

Certainly, according to Mr. M.... :shock:

 

[Nigel Goodwin]

as far as i know.. electronics is a science.. so is there any chance for miracles ??

Certainly, according to Mr. M.... :shock:

A miracle is simply something you don't understand YET! - so there's certainly scope for them in electronics.

As regards the circuit above, the chances of it working depend entirely on what's inside the 'little plastic box with legs on' - it's entirely possible that some makes of 74LS13 may work? - but using a logic chip in this kind of way is completely dependent on how it's constructed, and different manufacturers will make them differently.

But it's such a crap circuit anyway!, even if it worked it's only a novelty.

 

[akg]

A miracle is simply something you don't understand YET! - so there's certainly scope for them in electronics.

hmm...... :roll: ....u r a veteran so no arguments...
i'll have a check ... :?