Frustration

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Electronic can be quite frustrating.

I put together a circuit for a laser alarm.

It does not work.  

There is no way to tell if a design will be successful even if you follow the authors exact directions.

I will keep plugging away and reading Practical Electronics for Inventors.

:-)

Re: Frustration
On 14/05/2019 10:22 am, AK wrote:
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Making something is good and relatively easy, when it doesn't work and  
you try to find out why is when the real learning begins. Apart from  
those who are gifted and can learn with no effort I have no doubt the  
people giving you advice here have gone through the same experience.
Just stay calm and double check every thing. Best of luck.

Re: Frustration



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Re: Frustration
On Tuesday, May 14, 2019 at 4:45:42 AM UTC-4, Look165 wrote:


From the nonsense that you post, I can see why you believe that. If it were
 true we would still be trying to develop the first tubes, and using Alexan
derson Alternators to transmit Morse Code.

https://en.wikipedia.org/wiki/Alexanderson_alternator

Re: Frustration
On Mon, 13 May 2019 19:22:56 -0700 (PDT), AK

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If you look at the schematic and have some idea in your mind on how it
is supposed to work... you take your multi-tester and measure a few
things like the junction of the resistor and LDR.  If it is greater
than .6 volts the transistor (assuming you used a bipolar junction
transistor) should switch on.

Or are you using the 555 schematic?  (The trigger for a 555 has to be
less than 1/3 the supply voltage)  12V supply the trigger has to dip
lower than 4V...

Use logic and think about what is supposed to be going on then use the
meter to see what is really going on.

Re: Frustration
On Tuesday, May 14, 2019 at 5:53:47 AM UTC-5, default wrote:
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How specifically do I measure the junction of the resistor and the LDR?

I am using the 555 chip.

Andy

Re: Frustration
On Tuesday, May 14, 2019 at 6:21:59 AM UTC-5, AK wrote:
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I asked how to specifically do this, but did not get a reply.

got a voltmeter to test pin 3&6?
when pin 6 is >6v then pin 3 = 0v
when pin 6 is <6v then pin 3 = 9v

Can someone please show me how?

I assume one probe goes to the pin but where does the other go?

Thanks.

Re: Frustration
On Tue, 14 May 2019 04:27:22 -0700 (PDT), AK

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I'm not glued to the PC this morning...

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Measurements are assumed to be to ground or voltage minus unless
otherwise stated

I don't have the schematic in front of me but I think pin one is
ground on the 555?


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Re: Frustration
On Tue, 14 May 2019 04:27:22 -0700 (PDT), AK

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OK I found the schematic again... and now I understand he's using the
555 as a simple latch to keep the buzzer on indefinitely  

When there's light on the LDR Pin 6 should be low and pin 3 should be
high. (presumably you toggled the toggle switch to set those
conditions)

When light is interrupted Pin 3 goes low and turns on the buzzer until
you flip the toggle switch to turn it off again

Do you have the toggle switch wired as shown?  What voltage on pin 6
with light on the LDR, and what voltage on pin 6 with the light
interrupted (blocked)?  That voltage has the change significantly
between light and dark.  

When the voltage on  pin 6 is greater than the voltage on  pin 5, pin
3 should be high and the buzzer OFF.

When the voltage on pin 6 dips below 2/3d of your power supply voltage
pin three should go low and stay low, and the buzzer should be ON
until the toggle switch is toggled.

Re: Frustration
On 5/13/2019 9:22 PM, AK wrote:
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   Are you know using the 555 circuit.
                          Mikek

Re: Frustration
On Tuesday, May 14, 2019 at 7:29:08 AM UTC-5, amdx wrote:
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I do not understand your question.

Do you know of any circuit that will detect someone crossing a light path?

It does not necessarily have to use a laser.

Andy

Re: Frustration
On Tue, 14 May 2019 07:18:43 -0700 (PDT), AK

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Get a CdS photoresistor and a battery and a few resistors and a
flashlight and a DVM and experiment.

Start by connecting just the photoresistor to the DVM and measure
ohms.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Frustration
On 5/14/2019 9:18 AM, AK wrote:
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I'm surprised you have already forgot about the first transistor  
circuit you posted and then my response with a google search with 25  
more transistor circuits.
  After I posted you answered the question to someone else, yes you are  
using the 555 circuit.
  I'm disappointed, you had a chance to learn how to bias a transistor on
or off and then see how the changing resistance of your LDR would cause  
the switch on and off.
  You should find it interesting to bias a transistor to have the buzzer  
quiet, change the value of one resistor and make the buzzer buzz.
  Then put the original value back in with the LDR in parallel and see  
light make the buzzer go on and off.
You were to quick to abandon the original circuit.

                             Mikek

Re: Frustration
On Monday, May 13, 2019 at 10:22:59 PM UTC-4, AK wrote:
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Hmm, Well a common pitfall when starting in electronics is to copy all  
of some circuit.  Plug it in and find it doesn't work.  
A better approach would be to build up one little part of it.. make sure  
you know how that little part is supposed to work, and confirm it's  
working as expected.  (Or not and go figure out why.)  
Then add the next little piece.  

Do you have an oscilloscope?  

Re: Frustration
On Tue, 14 May 2019 07:19:09 -0700 (PDT), George Herold

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He is working on a pretty basic circuit. 555 monostable, with a LDR on
the trigger and buzzer on the output.

Re: Frustration
On Tue, 14 May 2019 07:19:09 -0700 (PDT), George Herold

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Here is the schematic
https://cdn.makezine.com/uploads/2013/11/laseralarm.jpg

He's using the 555 as a simple latch to turn on the buzzer until the
toggle switch resets it.

Re: Frustration
On Tuesday, May 14, 2019 at 11:22:42 AM UTC-4, default wrote:
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OK, I haven't used a 555 in decades, and have mostly forgotten how it works.

Maybe he could try a comparator and a S/R flip flop.. Or  
just a comparator to LED + resistor.  

George H.    

Re: Frustration
On Tue, 14 May 2019 09:34:32 -0700 (PDT), George Herold

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I had need of a break-beam photo detector in the 60's to keep my
motorcycle from being stolen.  I used a potentiometer, photocell, and
SCR for the latch to keep a doorbell ringing.  (the inductive kick and
contacts opening meant it wouldn't latch until I added an electrolytic
cap across the bell) We didn't have integrated circuits.

Re: Frustration
On Tuesday, May 14, 2019 at 9:19:12 AM UTC-5, George Herold wrote:
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I have tested the individual parts of circuit that I familiar with. I do not have a scope.


Re: Frustration
On Mon, 13 May 2019 19:22:56 -0700 (PDT), AK

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Electronics is frustrating if you put together things that you don't
understand, and they don't work. Why not just buy stuff all done?

If you do want to learn about electronics, start with very simple
circuits that you invent yourself, and do the math, and make it work.

Start with a battery and some resistors a DVM. Do the simple math all
along the way.

After that makes sense, add one big capacitor. Then an LED or two.
Don't move on until you understand it.

An introductory EE course at a community college would be hugely
helpful.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


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