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Author Topic: Question about alarm clocks and transistors  (Read 2434 times)

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Offline TheDarkLordTopic starter

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Re: Question about alarm clocks and transistors
« Reply #30 on: November 21, 2011, 12:40:34 PM »
And here it is :)


Thank you ;D That circuit looks much more complicated, but I'm always up for a challenge. Could you just briefly explain what's happening with the timer, in terms of input, trigger, output?


(Google "multivibrator tutorial" or similar to get a more in-depth look at them).


My mistake, I should have done that earlier. It's a pretty interesting topic!

Oops, just realized I didn't give the 555 any supply (that's what happen when you get interrupted by mundane stuff like dinner ;D) - Kicking myself and will change that as well.
Won't be any major changes though - I'll update and repost, but its 3 a.m. so it'll be after nap-time :)


I actually noticed the power supply was missing to the 555 - but you spotted it yourself before I could point it out :P


A potentiometer is a "potential divider" (metering out the potentials/voltages).

A trimmer can be either a trimming potentiometer, with "trimming" meaning something to adjust once or rarely/from time to time, while a normal potentiometer is something you adjust often (like eg. the volume on a radio/HiFi).

A trimmer can also mean a variable resistor, i.e. a resistor which is not used as a potential divider.
Some trimmers are made as just variable resistors (to save a bit in large scale production), but they're mostly found in consumer electronics like clock radios, cheap radios and such. Usually, you just use trimmer potentiometers as variable resistors by shorting the wiper to one end (as in this schematic).


OK, I see what a trimmer is now. For my purposes I'd rather use a potentiometer just so I'm able to have control over how much water gets dumped on me :D

Which of the first three products on this page would be the most suitable?

Potentiometer #1 and #3 are regular carbon track potentiometers, so is #2, but with an added on/off switch (all the way counter clockwise the switch is off).


So, if I use #2, then I won't need to install an additional switch for the entire circuit?


If you want it to be continually adjustable, you could use something like #1 of course - in that case, use as short leads as possible and connecting the metal encapsulation to either ground or V+ may be a good idea, as it will keep it from picking up noise. If the leads should act as antennas, a small cap (~10..100pF) can be used  at the board connection points.


Yes, I do want it to be continually adjustable. On the schematic you've said "20s - 72s". If I want this range to be slightly lower (maybe from 10s - 60s) what value potentiometer should I use? I know the equation is there, but I'm having a little trouble converting with all the zeroes :P Thanks.
I'll have to do some more reading into how it picks up noise - it's similar to how you told me I couldn't leave the base of Q2 'floating' earlier. It seems interesting, but I'm not able to completely understand the occurrence.
And just to clarify, what is "pF" in terms of F? Like "uF" is micro-Farads..

Thank you so much once again ;D I can honestly say that you're my role model - I want to be as knowledgeable as you are in this field. :) What is your profession anyway?

Offline Soeren

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Re: Question about alarm clocks and transistors
« Reply #31 on: November 21, 2011, 03:13:40 PM »
Hi,

Thank you ;D That circuit looks much more complicated, but I'm always up for a challenge.

Look at it as blocks, then it get's much easier :)


Could you just briefly explain what's happening with the timer, in terms of input, trigger, output?

You didn't see the description in the schematic?


OK, I see what a trimmer is now. For my purposes I'd rather use a potentiometer just so I'm able to have control over how much water gets dumped on me :D
You do have control with a trimmer as well just not as readily.


So, if I use #2, then I won't need to install an additional switch for the entire circuit?
You don't need to install a swith at all, when the alarm is off, there's no drain.


On the schematic you've said "20s - 72s". If I want this range to be slightly lower (maybe from 10s - 60s) what value potentiometer should I use?
Still 1MOhm. It's that value that gives the ~50s variance. Change R6 to 180k to get get around 9s as the lower limit.


I know the equation is there, but I'm having a little trouble converting with all the zeroes :P
??? Zeroes are easy to convert, but pay attention to what side of the decimal point they're at ;D

If you have a math calculator, you can enter a number like 47 as 47E-6 and 1MOhm as 1E6.
G  E9
M E6
k E3
m E-3
E-6
n E-9
p E-12


I'll have to do some more reading into how it picks up noise - it's similar to how you told me I couldn't leave the base of Q2 'floating' earlier. It seems interesting, but I'm not able to completely understand the occurrence.
And just to clarify, what is "pF" in terms of F? Like "uF" is micro-Farads..
The noise shouldn't be a problem as long as impedances (resistances) are kept reasonably low, so don't worry too much about it for now. The function, if the impedance is high, is comparable to a radio antenna.

1,000 pF (pico-Farad) equals 1nF
1,000 nF (nano-Farad) equals 1F


Thank you so much once again ;D I can honestly say that you're my role model - I want to be as knowledgeable as you are in this field. :) What is your profession anyway?
Thanks for the kind word, but be careful what you wish for  ;D
It probably doesn't come as a huge surprise that I'm an electronics engineer.
You're on the right track... Curiosity is probably the single most important trait to get you going in any technical discipline!


Please read what I wrote on the schematic and then tell me if you need any clarification :)
Regards,
Sren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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