I've done LED flasher type circuits before on here but usually they were for something someone wanted so they did specific things like fade in and out and so on.
So I thought for a little 10 minute project I would do one of the very first projects I ever made as a little boy. I was very proud when I made my first LED flash. it's not like now where people just load up the "blink" sketch in Arduino. this is a proper old school relaxation oscillator.
my original one had a few more components but I've managed to whittle this down to 3 resistors, 2 transistors and a capacitor + an LED obviously.
this particular circuit is known as a relaxation oscillator and there's lots of theory and stuff behind that but in extremely simple terms: it charges a capacitor until something "disturbs" it. in this case the "disturbance" is the threshold voltage of Q2 (the voltage at which the Base conducts) this quickly discharges the capacitor which results in a short blink.
which looks nicer than the conventional square wave oscillator which the LED stays on the same length of time as it is off
everyone loves a flashing LED
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| if you get this reference then you're ace. |
Would this work with a BC547 and a BC557?
ReplyDeleteI would imagine so - they are general purpose (just check the pinout)
DeleteI chuckled to myself when I read this project, the first thing I can remember building was an astable multivibrator, I put two LEDs @R1 & R4 {I think lol} they were red and green, and I put in a pot somewhere {R2 or R3?} and varied the flash rate.
ReplyDeleteThe family was mildly amused, especially my little 3 year-old {at the time} niece. What was also interesting and amusing, to me at least lol, was that at the time my father kept tropical fish, including something called neon tetra, which have a very fluorescent neon red and blue colouring. I noticed that when I got to a pretty fast flash rate and held the unit close to the aquarium that the neon tetra went straight to it - en masse - and followed it all around the tank...no other fish took any notice.
Although I had a pretty good flash rate, no angels or statues were ever embarrassed by their exposure...
Been great looking around your site, I've been away from hobby electronics for years, and you've kind of brought me back home to it, perusing your site I've built a Deacy amp and a few treble boosters, so far; although the Deacy is still looking for a cabinet...I'll stick a post up in the appropriate place, when I eventually get round to making/buying the cabinet lol
You know, I been away so long and have become so ignorant that I had no idea that lead solder isn't used any more, and I'd probably be lynched for using {if I still had any} trichloroethane for cleaning the boards lol
I hate the weeping angels. They creep me out every time. You site is fantastic, though.
ReplyDeleteHey Paul!
ReplyDeleteIf I wanted to add another LED to this (so I have 2 simultaneously flashing LEDs), what would that entail? Thanks!!
Hello Paul, I am stuck at home in Cape Town and I would like to build your flasher but my resistor collection only goes up to 1M Oh. Can I adjust the values in order to be able to use a 1M Ohm? Thanks - Nick.
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