/diy/ - Do It Yourself

I'm not an expert, but the polarity of the transistor in the circuit seems to be incorrect.

>>464786
there's some freaky shit going on in that circuit
maybe you could try a latch with the output connected to the input via some capacitors and big resistors

>>464787
really, what you want is a schmitt trigger set up to charge or discharge a capacitor depending on its state
just put a resistor to a big capacitor from the output and to ground, then put the high end of the capacitor to the input

>>464776
Try this one.

OP here,

Thanks guys! You are all a great help. Another FYI we are using a 9volt battery.

>>464786
I'm not surprised you'd think that. A lot of EEs don't even know this magic.

http://en.wikipedia.org/wiki/Bipolar_junction_transistor#Regions_of_operation

- Reverse-active
>: By reversing the biasing conditions of the forward-active region, a bipolar transistor goes into reverse-active mode. In this mode, the emitter and collector regions switch roles. Because most BJTs are designed to maximize current gain in forward-active mode, the βF in inverted mode is several (2–3 for the ordinary germanium transistor) times smaller. This transistor mode is seldom used, usually being considered only for failsafe conditions and some types of bipolar logic. The reverse bias breakdown voltage to the base may be an order of magnitude lower in this region.

In OP's circuit the capacitor is initially uncharged. In this state most of the current flowing through the 1k resistor will go into it. Current can not enter a charged capacitor. Once the cap is charged current will start pushing up against the 2N2222. This puts it into reverse mode allowing it to conduct through the LED and discharge the capacitor.

Does anyone have some good EE books for someone who is interested in schematics and electronic engineering?

>>464776

>>464811
If an EE doesn't know reverse biased BJT's (or any applicable component, really, like diodes), they are fucking fail. It's covered in practically every introductory electronics course at every certified school I've ever seen. The reverse bias specs are right there underneath the forward bias specs of these parts in every major supplier (newark, mouser, digikey, etc).

>>464833
I didn't say they weren't aware of reverse mode. Using it to do something useful like flashing an LED isn't something commonly taught. Reverse mode is just fail mode to most of us.

>>464833
>>464838

It isn't just the reverse mode operation or the B-E breakdown, as those modes aren't enough to make the circuit oscillate. There's some dynamic negative resistance involved in the transistor breakdown which makes the circuit work. "Work" in a loose sense, as it's a bad circuit relying on unspecified parameters with unspecified tolerances and temperature coefficients.
You can also reverse the transistor. It'll still work, but you'll need much higher supply voltage.

OP: >>464823 is a much better circuit if you want to explain its operation or analyse it.

>>464813
An excellent book:
http://thepiratebay.sx/torrent/3965200/The_Art_Of_Electronics

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