Author Topic: How comes a monostable 555 being more expensive than a 8-pin microcontroller?  (Read 2124 times)

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Offline technix

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It's amazing how tenaciously some people like to hang on to their ideas about how things used to be done. Using a programmed device isn't "cheating", it's simply how this kind of thing is done nowadays. Other than analogue functions (eg. 4052) and specialist I/O, I can't remember the last time I used a 74 series logic chip. The cost is all in the packaging, board space and assembly; what's actually inside that SO14 package really doesn't matter at all. (Add 10p for programming if you really want).
My original idea was two Schottky diodes into a cap into LM393 into 555, with a side car of a TL431. If I go the PIC route the LM393 and the 555 are gone, but the TL431 + pot reference circuit and the Schottky diode peak detector is still there.
 

Offline CopperCone

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It's just a different way of thinking. That particular PIC *is* a dual comparator.

Don't think of it as a programmed device at all; just think of it as a compact, high temperature device, a bit like an LM293 but with a longer part number.

but it is a programmed device and there are all sorts of quirks of using a programmed device that you just can't ignore. The silicon is inherently more complicated and the process is more prone to quality problems because there are more complex inspection and verification steps.
 

Offline AndyC_772

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Do you have a concern that's specific and quantifiable enough to address?

Offline schmitt trigger

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I did a job last year which required a couple of comparators, on a tiny PCB which would withstand 125 deg C.

A PIC was the best option commercially. It runs code which programs the I/O registers at power-up, then sits in an endless loop.

It's amazing how tenaciously some people like to hang on to their ideas about how things used to be done. Using a programmed device isn't "cheating", it's simply how this kind of thing is done nowadays. Other than analogue functions (eg. 4052) and specialist I/O, I can't remember the last time I used a 74 series logic chip. The cost is all in the packaging, board space and assembly; what's actually inside that SO14 package really doesn't matter at all. (Add 10p for programming if you really want).

I'm not sure I've *ever* actually used a 555 timer in a commercial product. There's always some little corner of a microcontroller or FPGA available instead.

*Gasping for air*
You mean...I can no longer use my dual triode, Eccless-Jordan multivibrator anymore? There are a pair of triodes inside an ECC83/12AX7, so that is LSI in my book.  ;D
 


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