Electronics > Projects, Designs, and Technical Stuff
Need some help with a 555 timer circuit
Ian.M:
A couple of hours, most of which was wasted on the switch bounce generator- see below. I can layout a basic 555 sim in under ten minutes then its just a matter of a little copy/paste to daisy-chain them and gutting most of the timing components round U1. I use a mouse macro utility, so a lot of the layout is just muscle memory following my train of thought. Probably the most tedious chore is reordering reference designators. D3 got away from me as I originally had two more Schottkys for ESD protection at the input, but I decided they were superfluous, removed them and forgot to rename the remaining diode as D1.
There is no separate schematic file as I did it all in LTspice. If you delete all the simulation crap at the bottom, you can export the netlist, but unless your preferred PCB design package supports working from a raw netlist in a friendly manner, you'd probably do better to manually redraw it.
N.B. the switch bounce portion of the sim is buggy and inefficient. I've spent the better part of yesterday sorting that out so it simulates switch bounce efficiently.
Pizzashape23:
Yeah, I just finished redrawing it and it looks great, seriously i cannot express how much of a legend you are and how much help you have provided.
Ian.M:
Please at least breadboard it and confirm correct operation before you start ordering PCBs! When you get to the layout, I'd probably put a footprint for a 500K multi-turn preset for the timing resistor, (with a 10K 'end-stop' resistor in series), and some spare footprints for extra timing capacitors in parallel, so you can adjust the pulse-width over a considerable range.
Pizzashape23:
Of Course, and yeah, the pot and extra footprints sounds like a great idea.
ledtester:
There are possible solutions using a couple of NAND gates or NOT gates:
https://www.electronics-tutorials.ws/sequential/seq_3.html
so you could use a single CMOS logic IC, e.g. a CD40106 or a CD4093.
There are also chips dedicated to this purpose, e.g.: CD4538, 74LVC1G123:
https://www.nexperia.com/products/analog-logic-ics/synchronous-interface-logic/multivibrators/74LVC1G123DP.html
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