Hi,
I'm trying to make an LED blink without using a microcontroller or two transistor oscillator circuit. Basically with one capacitor, transistor (2N3904), LED and resistors, but i cant make it blink.
I found on youtube this video about a single transistor oscillator circuit where, for how much I was able to understand, is relayed on the resistance of the transistor and the "braking" point of the component or something like this, but I'm not shore if the source of the video is reliable. Can somebody check it and say if is possible to make an oscillator circuit with one capacitor and transistor and is there any other method to make it blink? here is the link to the video:
You can make a single transistor oscillator/LED blinker with a resistor, capacitor and a unijunction transistor (UJT). Search google images for "unijunction transistor relaxation oscillator"
Wawa:
IMHO all questions should be arduino related.
IMHO this is very related to Arduino - Arduino alone does very little without other electronic. This is nice example of "strange" behavior that can be used for an Arduino project or may lead to an unexpected failure if unknown. Here is some explanation of the circuit.
The old-school answer to this question is "use a unijunction transistor relaxation oscillator". I've
never seen a unijunction transistor, even way back when, I doubt you'll find one these days!
You are missing the point: the links claim ANY common BJT can be used this way - provided voltage is high enough. "Negative resistance" and quantum tunneling is involved, quite interesting. I will definitely try if and how this works when I get time.
No such thing these days, use parametric search on any of the reputable semiconductor suppliers web sites and there is just about a different semi for every application.
In the good old days, (showing my age), it was a handful of different semiconductors that were readily available that had to do most of your projects.
LM555, OC44, OC70, 2N3055, BC546 to 549, BC556 to 559, TIP31 and 32, LM741, LM3900, LM78XX, LM723, LM380
The reverse biased EB junction would normally work like a zener diode due to its high doping
concentration (in the emitter at least). It won't be optimized for negative resistance behaviour though,
and over driving the junction backwards is a very easy way to fry a BJT, so keep the current limited.
Hi,
I've thought to an idea to test if will work to use a NPN mosfet for discharging the capacitor connecting the gait of the mosfet to the positive side of the capacitor, but i must do the math for the voltage levels in order to close the mosfet when reached the voltage needed and also there are some additional things for the mosfet so it can open when the voltage is low (a resistor or something like this), but definitely I'll try to find a UJT transistor, sounds fun hehe
Tested and it WORKS. I used unknown NPN BJT (fake LM35), circuit from link in post #9 and the LED is flashing nicely. 9V was not enough but adding one AAA to get 10.5V made it. There is about 9.8 V over the cap and around 8.2V CE voltage (measured by DMM, changing quickly; LED blink much slower when measuring the transistor).
