CD4093 - Part One (Finally...maybe...)
I love a good Schmitt Trigger IC (well, who doesn't?), but I had no fun at all when I tried to make a circuit using the CD4093 Quad Schmitt Trigger IC configured as a "mains" power detector, as documented on a previous blog.It was a disaster, and the whole blog ended up being about the ever reliable CD4017 standing in and actually working as a mains detector. Now, with some experience but also some trepidation I return to the CD4093, firstly as a legitimate one shot Schmitt Trigger NAND gate, and then maybe as a magnetic window/door alarm thingy. If I end up using the CD4017 again for this project, I promise not to mention the CD4093 ever again!
The first order of business is to plug in a chip and make sure it's not full of little socks (long story) and then configure one of the NAND gates available to act as a Schmitt trigger (in this case to set the sensitivity of a light dependent resistor). Note that all other inputs on the other three NAND gates are pulled high (or low) as recommended, although in quick testing I abandoned that for brevity.
The circuit I have in mind for the quad-NAND gate IC needs all four gates, so I set about testing all four. In the first chip tested, pins 4/5/6 didn't work! I swapped the miscreant out for another chip from the same batch and...pins 4/5/6 failed. Was the whole consignment on the nose? I dug into a bucket and found a CD4093 from another supplier and after testing found that...pins 4/5/6 were duds! What?
Mmmm, finally I twigged and changed the ultra-cheap "Mr Crappy" breadboard for another ultra-cheap breadboard (thanks Ben Eater "not all breadboards are the same") and then success, as all four NAND gates on all three chips tested fine and as expected (see video below). The next step will be to hook up the hall effect sensor etc., and then maybe in Part Two of this blog we might finally see a successful CD4093 project and my faith in Schmitt Triggers will be restored.
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