The 555 of the 70's: The Unijunction Transistor
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- เผยแพร่เมื่อ 27 ก.ค. 2024
- Have you ever heard about unijunction transistors (UJT)? In this video you can see what these transistors can do and what they are good for.
Parts and Tools:
UJT 2N2646: amzn.to/3zzz4PW
PUJT 2N6027: amzn.to/3aOH3yq
Camera: amzn.to/3HkUJO0
USB Oscilloscope: amzn.to/3twlp8q
Multimeter:amzn.to/3NLlTjb
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0:00 - Introduction
0:17 - Difference Between Unijunction and Bipolar Transistor
1:39 - Function of an Unijunction Transistor
4:25 - UJT as Relaxation Oscillator
6:17 - The Programmable UJT (PUJT)
7:17 - Programmable UJT as Voltage Controlled Oscillator (VCO) - วิทยาศาสตร์และเทคโนโลยี
I found one in a box of parts given to me by an oldtimer and looked it up the datasheet. I came to your video and described it beautifully. Certainly I subscribed for a well done explanation sir.
Muy bien puesto el titulo !!!!!
I have a whole ton of the PUJ's 2N6027, time to play with them I guess. Thanks for the video and useful information, great as always Doc!!
I find they can be pretty good for interfacing simple resistor, or capacitive sensors to microcontrollers. the "variable property" into a digital pulse chain. That way... Rather than waiting around for a measurement, can use pin interrupts to record time of event, with time difference being the reading.
Circuit I suggest is to feed both gate pin and Trigger voltage pin by seperate constant currents. As long as current to trigger pin is largest..it's voltage is guaranteed to rise faster than gate...thus put can't latch on.
Trigger voltage generated by resistor to ground... V=i*R etc.
Constant current also make timing linear. And also avoids any issue with resistance of wire to sensor.
I have a lot of fun witn 2N2646 in the 70' years . But now, I play with rpi2040, thé times are changing
Fascinating! I had also never heard of these. (Not surprising as I really don’t know much about analog stuff)
Perfect
I've killed cmos 555s when using a variable capacitor as sensor... After a fair bit of head scratch... I concluded that a charged large capacitance, has a certain amount of stored energy.
If capacitance reduced suddenly... Stored Energy remains constant. Voltage has to go up to compensate for smaller capacitance.
Put circuits more robust under such conditions, as they will of course discharge cap if voltage goes higher than threshold. Such may muck up a sensor reading... But that's usually preferable to a component failling.
Always at the top!
You have instructed on how to calculate voltage V(p), and I have understood it. However, you haven't provided guidance on how to calculate V(v) (Valley Point). Is there a way to calculate V(v) (Valley Point) ?
You cannot calculate the valley point. It's a parameter of the UJT and can be found in the data sheet.
💜💙
How you manage to get a real one? Nowadays are all PNP fakes. Tried 4 different suppliers. All sent same PNP crap. 🙁
Maybe I was just lucky to get a functioning one.