Help on a Simple LED and Short Beep Circuit

Thread Starter

n2glox

Joined Aug 29, 2009
38
Well, if you hooked it up in reverse polarity, you probably fried it.

Didn't think to put in a diode to protect against that. Sorry.

I'm surprised you didn't fry it when you ran it on 17v. It wasn't designed for that much voltage.

You probably fried the LED and the 7805 regulator. Replace the LED and the 7805. Or, you could see if you can get the LED to light up.

If you're getting 5v at the output of the regulator, it's probably OK.

If the LED doesn't come on, it's fried.
After I fix the fried stuff and switch out the speaker, I will re-run experiments with different set ups to see if the weirdness is still there. The frying came after i noted the weirdness above. I want to see what it does exactly, and I need to write down the exact behavior.
 

Thread Starter

n2glox

Joined Aug 29, 2009
38
Simply connect your normally open reed switch to the test probes terminals of continuity tester circuit. But you will need to trade your 555 IC by LM 3909 with some one.
well I already have a circuit built based on SgtWookie's suggestions. And I would prefer not to rebuild. But why the 3909 vs 555?

Jeff
 

SgtWookie

Joined Jul 17, 2007
22,230
Jeff,
The LM3909 is a long-obsolete LED flasher that was designed to operate from a single 1.5v battery. It would not work with your 12v supply.
 

Thread Starter

n2glox

Joined Aug 29, 2009
38
Jeff,
The LM3909 is a long-obsolete LED flasher that was designed to operate from a single 1.5v battery. It would not work with your 12v supply.
Thanks.

I have now replaced the 7805 and the speaker and I still get nothing. I figure that I need to check the 2n2222a, the 555, adn maybe the diode to see what got fried.

How do I use my voltmeter to check these components without taking a part the circuit? Do I need to check the capacitors? How do I check to see if the 7805 is putting out the 5v?

I appreciate any help.
 

SgtWookie

Joined Jul 17, 2007
22,230
Here's a start:

1) Make sure that S1 is open (no connection), 12v applied.

2) Set meter to measure DC volts, 20v range or autorange.

3) Measure from the base to the emitter of Q1. You should measure nearly 0v. If not, S1 is closed (open it). If S1 is open, Q1 is shorted; replace it.

4) Measure from the collector to the emitter of Q1. You should measure about 12v.

5) Measure from the emitter of Q1 to GROUND. You should measure 0v. If not, there is a problem with the connection between the emitter of Q1 and GROUND.

6) Measure from the IN terminal of the 7805 to GROUND (12v return) - you should measure about 12v. If not, the 12v supply is off or there is a wire broken somewhere between the 12v supply and the IN terminal.

7) Measure from the IN terminal of the 7805 to it's ground pin. You should measure about 0v. If not, Q1 may be shorted.

8) Measure from the junction of R3/S1 to GROUND. You should measure about 12v. If not, R3 may be open.

9) Close S1.

10) Measure from the base of Q1 to GROUND. You should measure about 0.7v-0.9v. If much higher, Q1 is blown. If near 0v, base is shorted to emitter.

11) Measure from the collector of Q1 to the emitter of Q1. You should measure less than 0.3v. If much more, Q1 is burned open.

12) Measure from the GROUND terminal of the 7805 to the IN terminal of the 7805. You should read about 12v. If not, check the connection between Q1 collector and the 7805 GROUND terminal.

13) Measure from the GROUND terminal of the 7805 to the OUT terminal of the 7805. You should read about 5v. If not, the 7805 is bad or the 555 timer is shorted internally.
 

Thread Starter

n2glox

Joined Aug 29, 2009
38
Here's a start:

1) Make sure that S1 is open (no connection), 12v applied.

2) Set meter to measure DC volts, 20v range or autorange.

3) Measure from the base to the emitter of Q1. You should measure nearly 0v. If not, S1 is closed (open it). If S1 is open, Q1 is shorted; replace it.

4) Measure from the collector to the emitter of Q1. You should measure about 12v.

5) Measure from the emitter of Q1 to GROUND. You should measure 0v. If not, there is a problem with the connection between the emitter of Q1 and GROUND.

6) Measure from the IN terminal of the 7805 to GROUND (12v return) - you should measure about 12v. If not, the 12v supply is off or there is a wire broken somewhere between the 12v supply and the IN terminal.

7) Measure from the IN terminal of the 7805 to it's ground pin. You should measure about 0v. If not, Q1 may be shorted.

8) Measure from the junction of R3/S1 to GROUND. You should measure about 12v. If not, R3 may be open.

9) Close S1.

10) Measure from the base of Q1 to GROUND. You should measure about 0.7v-0.9v. If much higher, Q1 is blown. If near 0v, base is shorted to emitter.

11) Measure from the collector of Q1 to the emitter of Q1. You should measure less than 0.3v. If much more, Q1 is burned open.

12) Measure from the GROUND terminal of the 7805 to the IN terminal of the 7805. You should read about 12v. If not, check the connection between Q1 collector and the 7805 GROUND terminal.

13) Measure from the GROUND terminal of the 7805 to the OUT terminal of the 7805. You should read about 5v. If not, the 7805 is bad or the 555 timer is shorted internally.
After Step 9 the Q1 came out as screwed. SOme of the first 8 steps were a little confusing, but I need to replace Q1 before confirming the other stuff.

I may try to make temp connections before soldering the q1 so I can make certain it works.

Thanks again.
Jeff
 

SgtWookie

Joined Jul 17, 2007
22,230
OK, if you measured about 12v on the base of Q1 in step 10, then Q1 is toast.

I kind of set it up that way so that Q1 would be sort of a crude fuse. If the circuit is pulling more than about 100mA current continuously, Q1 will burn up rather than the rest of the circuit.

Radio Shack stocks 2N2222/PN2222 transistors in a TO-92 plastic case. They're actually less expensive than fuses; just a bit more effort to replace.

If you happen to buy the 15-transistor assortment that RS stocks (about $2) they call them all 2222-type NPN's, but only about 4 of them will actually be 2n2222-type transistors. The others are fine for hobby-type projects (usually 2n4401, 3904, etc), but you really want the 2n2222's for this application.
 

Thread Starter

n2glox

Joined Aug 29, 2009
38
OK, if you measured about 12v on the base of Q1 in step 10, then Q1 is toast.

I kind of set it up that way so that Q1 would be sort of a crude fuse. If the circuit is pulling more than about 100mA current continuously, Q1 will burn up rather than the rest of the circuit.

Radio Shack stocks 2N2222/PN2222 transistors in a TO-92 plastic case. They're actually less expensive than fuses; just a bit more effort to replace.

If you happen to buy the 15-transistor assortment that RS stocks (about $2) they call them all 2222-type NPN's, but only about 4 of them will actually be 2n2222-type transistors. The others are fine for hobby-type projects (usually 2n4401, 3904, etc), but you really want the 2n2222's for this application.
It worked. I replaced the 2n2222 and it works fine now. Now I have to figure out the speaker. THe buzzer I bought, a new one from RS is rated at 1.5v minimum and is not making much noise, very soft (really inaudible). My auto-detecting voltmeter is not fast enough to detect the voltage. Any suggestions? I am scouring Mouser and Jameco, but the lowest is about 1.5 v. I am also looking at some online sources about different kinds, but not finding much since voltage usually relates to loudness.

Thanks again for all of your patience and help.
 

SgtWookie

Joined Jul 17, 2007
22,230
Which circuit are you using now? I just noticed the last one that I posted was Alerter3, but you marked up and posted Alerter2?

Anyway, if S1 is closed (garage door open) or you short the collector of Q1 to ground, and C1 is shorted to ground, the buzzer should sound continuously.
 

talking

Joined Dec 10, 2009
12
There is just one very bad circuit design in the circuit you posted, using the 78L05 regulator.

You should NEVER turn off a 3-terminal regulator by letting the common pin float as the output will rise to nearly the input voltage.
If any devices powered by the regulator are connected to ground, they will be instantly damaged.
You get away with this design-mistake by having everything floating, but it is never to be recommended.
 
Last edited:

SgtWookie

Joined Jul 17, 2007
22,230
There is just one very bad circuit design in the circuit you posted, using the 78L05 regulator.

You should NEVER turn off a 3-terminal regulator by letting the common pin float as the output will rise to nearly the input voltage.
That's the idea. The output across the regulator, and within the circuit, will soon be 0v.

I don't know where you got the idea that you can't do that, but you are incorrect.

If any devices powered by the regulator are connected to ground, they will be instantly damaged.
There IS no other path to the 12v return than through the collector emitter junction of Q1.
You get away with this design-mistake by having everything floating, but it is never to be recommended.
The entire circuit IS floating; it's powered by a wall wart, and there IS no real ground - furthermore, if any part DID connect to a real ground, it would have no effect, since the entire circuit is isolated by the transformer in the wall wart.

Would it make you more happy if I re-labeled +12v as 0v, and changed ground to -12v?
 

Thread Starter

n2glox

Joined Aug 29, 2009
38
Which circuit are you using now? I just noticed the last one that I posted was Alerter3, but you marked up and posted Alerter2?

Anyway, if S1 is closed (garage door open) or you short the collector of Q1 to ground, and C1 is shorted to ground, the buzzer should sound continuously.
I am using #2. #3 is the next project after I got the first one working. I am using #2 with the modifications I indicated (s2, deleted R5, and added the 10000 ohm resistor to Q1). I am not certain what you are suggesting. It does beep but it so soft it can only be heard from a few inches. I just want it louder. I assume that I do not have enough voltage for the buzzer. Is there any way to get it louder?

Thanks

Jeff
 

Thread Starter

n2glox

Joined Aug 29, 2009
38
BTW i still want it to beep every 20 seconds like it does now, just louder. Is there a way to run the power off of the input with a resistor or something, maybe a trimpot yet still switch that source of power on using something else?

Jeff
 

SgtWookie

Joined Jul 17, 2007
22,230
I am using #2. #3 is the next project after I got the first one working. I am using #2 with the modifications I indicated (s2, deleted R5, and added the 10000 ohm resistor to Q1).
OK, that's fine.
Just for future reference; the original file format was .png - you edited it and saved it as a .jpg file. For schematics, .png format is much preferred, as this format preserves all of the original information in the drawing and doesn't get blurry/fuzzy like .jpg format files do. Once you save an image in .jpg format, trying to revert to .png format is a problem.

MS Paint can save in many different formats, but for here, .png is preferred.

I am not certain what you are suggesting.
OK then - the 555 pins 2 and 6 are connected together, and also to one side of C1. Run a wire from pin 2, 6, or that same side of C1 to the emitter of Q1, and the buzzer should sound continuously.

It does beep but it so soft it can only be heard from a few inches. I just want it louder. I assume that I do not have enough voltage for the buzzer. Is there any way to get it louder?
Did you try just taking the buzzer out of the circuit and connecting it up to 12v? Right now, it's running off of 5v maximum.

The regulator was originally put in because of the buzzer's 5v requirement.

You could increase the output voltage of the 7805 regulator by adding resistance between it's GND terminal and the junction of where the collector of Q1 joins the ground side of C3. A 1k resistor should bring the output of the regulator to around 10v.
 

Thread Starter

n2glox

Joined Aug 29, 2009
38
OK, that's fine.
Just for future reference; the original file format was .png - you edited it and saved it as a .jpg file. For schematics, .png format is much preferred, as this format preserves all of the original information in the drawing and doesn't get blurry/fuzzy like .jpg format files do. Once you save an image in .jpg format, trying to revert to .png format is a problem.

MS Paint can save in many different formats, but for here, .png is preferred.
I will follow convention. I use a Mac, MS Paint is primitive. :)

Did you try just taking the buzzer out of the circuit and connecting it up to 12v? Right now, it's running off of 5v maximum.
Would that not make it continuous? If not please look at the Schematic below 2B. I added a red line representing running a line directly from the speaker to the 12v in. Is that what you are recommending?



The regulator was originally put in because of the buzzer's 5v requirement.

You could increase the output voltage of the 7805 regulator by adding resistance between it's GND terminal and the junction of where the collector of Q1 joins the ground side of C3. A 1k resistor should bring the output of the regulator to around 10v.
In the Second Schematic below - 2A, I added a resistor in red (1K) is that the approximate location?



Both 2A ad 2B show all of the changes I made to the circuit's original design.

If I go with the 1k Resistor, would going with a lower resistor decrease the voltage or do I have to go higher than 1k? I might use a trimpot and allow for adjustment of the voltage. I do not want to go higher than 10v, but I might want something in between 5 and 10v.

Thanks, Jeff
 

Thread Starter

n2glox

Joined Aug 29, 2009
38
Close, but no seegar!

Like this:


The dashed wire is a temporary jumper. If the switch is closed, you'll cause problems.
Thanks. I got it all put together. The speaker is a little too soft, but workable. The confusing thing is that when I added the resistor as above I got more voltage and more power, and on my workbench using about 12.5 volts (compared to 12.0 in the install location) I got a nice volume. I take the board upstairs and hook it up and the buzzer goes soft. I do wonder if I am losing some voltage as the electricity travels through the reed switch. (S1). S1 is 30' forward of the LED and speaker and i ran wire that was too heavy (18ga). Could that be sapping my voltage enough to wreak havoc? I looked it up adn it seems that 18ga wire only loses about .5 Ω per leg of the trip to the switch and back.


Now that i have a decent enough understanding I am going to use your expanded schematic (#3) and breadboard it to help me figure out some stuff.

After breadboarding it I will actually take it to the install location on the breadboard and debug it before soldering. i am learning my lesson.

I May also try it without the 7805 and play with some of the values to see what happens. I usually learn best by trying reading, and trying some more.

BTW, how does the resistor on the common of the 7805 add more voltage?

I have learned a lot through this little project. now to have more fun. I need some parts and more breadboards. I am also going to build a power regulator for the breadboard to clean up the power and allow some adjustment. I have seen powered breadboards, but those are pricey. I have seen several designs that seem good.

Thanks again. if you are ever in central MO (columbia) give me a message and I will treat you to good meal and a beer.

Thanks

jeff
 

SgtWookie

Joined Jul 17, 2007
22,230
Thanks. I got it all put together. The speaker is a little too soft, but workable.
Perhaps if you get into a lively conversation with it, it will become more vociferous. ;)

The confusing thing is that when I added the resistor as above
You have not shown where you are adding a resistor.
I got more voltage and more power, and on my workbench using about 12.5 volts (compared to 12.0 in the install location) I got a nice volume. I take the board upstairs and hook it up and the buzzer goes soft.
Do I dare ask what Dr. Sigmund has to say about this?

I do wonder if I am losing some voltage as the electricity travels through the reed switch. (S1). S1 is 30' forward of the LED and speaker and i ran wire that was too heavy (18ga). Could that be sapping my voltage enough to wreak havoc? I looked it up and it seems that 18ga wire only loses about .5 Ω per leg of the trip to the switch and back.
18 gauge wire has an enormous current carrying capability for this project.

You could reduce R3 from 2.4k to 1.2k if you wished.

Now that i have a decent enough understanding I am going to use your expanded schematic (#3) and breadboard it to help me figure out some stuff.

After breadboarding it I will actually take it to the install location on the breadboard and debug it before soldering. I am learning my lesson.

I May also try it without the 7805 and play with some of the values to see what happens. I usually learn best by trying reading, and trying some more.
That's the only real way to learn anything - trial by experimentation.

BTW, how does the resistor on the common of the 7805 add more voltage?
Ohm's Law.
The 7805's output voltage depends upon its' current sink through its' GND terminal. The nominal sink current for a 7805 regulator is 5mA. So, if you increase it's resistance to ground, what do you wind up with?

I have learned a lot through this little project.
That was the idea. ;)

Now to have more fun. I need some parts and more breadboards. I am also going to build a power regulator for the breadboard to clean up the power and allow some adjustment. I have seen powered breadboards, but those are pricey. I have seen several designs that seem good.
Buy an "Electronics Learning Lab" from Radio Shack. They are on sale at the moment.

You will learn a lot from that purchase.

If you don't care about learning stuff, you could get one of these:
http://www.mpja.com/prodinfo.asp?number=17710+TE
But you'll miss out on how to design and build something like that.

Thanks again. if you are ever in central MO (columbia) give me a message and I will treat you to good meal and a beer.
Just ONE beer? :eek:
Never met a Marine before, have you? ;)

Happy Holidays to you and your family.
 

Thread Starter

n2glox

Joined Aug 29, 2009
38
I added R5, a 2.4k Resistor gave most volume. I may try the 1.2k

As a Marine you get as many as you want. I have friends in most services and friends who were once active in the marines, army, navy, and air force. Always a free meal and beers for service men and women. It would be an honor. :)



Thanks for the tip. I am getting my son a kids electronics kit, and maybe the radioshack for me.

Thanks

Jeff
 
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