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Altoids can Morse Code Oscillator
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Nginuity
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Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas

PostPosted: Sun Jan 14, 2007 2:16 pm    Post subject: Altoids can Morse Code Oscillator Reply with quote

Hey everyone. I finally finished that morse code oscillator I was working on. It works okay for what it is, but I have some serious heat dissipation issues I need to look into for next time. The caps going to ground get real hot if I keep the morse keyer depressed, and, the pitch gets higher as it heats up too. That 500 ohm pot is REAL hot to the touch. I think with beefier components (I was thinking of replacing the ceramic caps with tantalum), and a diode in between pin 7 and pin 2 of the 555 timer, and a zener diode between pin 2, and the 15 K resistor will bring down the heat a bit. The diodes were suggested for a more stable duty cycle anyway.

Here are a few pictures:




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BronzeG3
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Joined: 30 Apr 2006
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PostPosted: Sun Jan 14, 2007 7:01 pm    Post subject: Reply with quote

Looks nice. Much cleaner than the stuff I make.
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Nginuity
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Joined: 13 Nov 2006
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Location: Dallas, Texas

PostPosted: Sun Jan 14, 2007 7:21 pm    Post subject: Reply with quote

BronzeG3 wrote:
Looks nice. Much cleaner than the stuff I make.


Thanks! Any ideas what is causing that heat? It is mainly that cap at the bottom of the perf board, and the pot. It was almost too hot to touch. I am almost convinced that the components I am using arent rated for quite the amount I am giving them.

Oh, I did this with that Metcal rework station I was telling you about. It makes easy work of soldering. When I first got it a few years ago, I had to learn how to be extremely light to the touch with stuff, and as you can see, sometimes I will still solder in sockets for an IC if I know a lot of heat will be around. Just in case.
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BronzeG3
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PostPosted: Sun Jan 14, 2007 10:04 pm    Post subject: Reply with quote

I think the heat is just from the current that gets pulled through it. Beefier components would probably help. I was also thinking, would it be possible to attach surfaces of the hot components to the case using thermal grease or similar? It would make the case a giant heat sink!
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Nginuity
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Joined: 13 Nov 2006
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Location: Dallas, Texas

PostPosted: Sun Jan 14, 2007 10:12 pm    Post subject: Reply with quote

It might be possible to have them hit the top.

The only problem though, is when you hit metal, or any other conductive object with a ceramic cap, it changes it's charge/discharge capabilities.

It's fun to put your fingers around the capacitor going to ground and listen to the tone get higher Smile

I also think the diodes will be a good idea. The pitch wouldn't change as much if I added them.
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Sun Jan 14, 2007 10:15 pm    Post subject: Reply with quote

Nginuity wrote:
BronzeG3 wrote:
Looks nice. Much cleaner than the stuff I make.


Thanks! Any ideas what is causing that heat? It is mainly that cap at the bottom of the perf board, and the pot. It was almost too hot to touch. I am almost convinced that the components I am using arent rated for quite the amount I am giving them.

Oh, I did this with that Metcal rework station I was telling you about. It makes easy work of soldering. When I first got it a few years ago, I had to learn how to be extremely light to the touch with stuff, and as you can see, sometimes I will still solder in sockets for an IC if I know a lot of heat will be around. Just in case.


Nice job, the finished project looks very nice! Very Happy

If you post the schematic we could see if there is anything obvious that is causing the heat. I am concerned if the cap is heating up, if a cap isn't over voltaged I have never felt one get hot...
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Nginuity
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Joined: 13 Nov 2006
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Location: Dallas, Texas

PostPosted: Sun Jan 14, 2007 10:35 pm    Post subject: Reply with quote

Alan wrote:
Nice job, the finished project looks very nice! Very Happy

If you post the schematic we could see if there is anything obvious that is causing the heat. I am concerned if the cap is heating up, if a cap isn't over voltaged I have never felt one get hot...


It's just a 555 timer running in Astable operation:



The values have been changed as follows:

R1 is 3.3K
R2 is 15 K
C2 is 4.7 uf
C1 is 4.7 uf

I also added a connection for pin 5 (control voltage, this is the one getting hot) to ground with a .01uf in between, and the 500 ohm pot in between ground and the speaker, which is taking on some heat too. I did this because in astable mode this decouples the circuit and prevents interference, as I am eventualy going to use this circuit to moduilate on a carrier frequency for ham radio. The pot is for volume control. They very well may be undersized for the job, though.
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Alan
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PostPosted: Sun Jan 14, 2007 10:39 pm    Post subject: Reply with quote

What is the voltage rating of the electrolytic cap?
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Nginuity
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PostPosted: Sun Jan 14, 2007 10:41 pm    Post subject: Reply with quote

Alan wrote:
What is the voltage rating of the electrolytic cap?


The one going to the speaker? 25 volts. The others are ceramic disk.
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Nginuity
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PostPosted: Sun Jan 14, 2007 10:44 pm    Post subject: Reply with quote

Nginuity wrote:

C2 is 4.7 uf


Sorry, correction, C2 is .047 uf, not 4.7
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J0ker
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Joined: 15 Jan 2007
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PostPosted: Mon Jan 15, 2007 11:09 pm    Post subject: Reply with quote

which speakerphone r u using? Is it low ohm? Check datashit for 555 IC - absolute maximum output current usually about 100 mA. So if u r using 8 ohm speakerphone u will have 9/8 = more then 1A output current... actually some less because output capacitor have some reactive resistance. Anyway check output current.
Also it is possible C2 capacitor is shorted - it should not getting hot in any situation (in working voltage range), because capacitor does not dissipate power.
________
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Last edited by J0ker on Mon Jan 31, 2011 1:23 pm; edited 1 time in total
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Alan
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PostPosted: Tue Jan 16, 2007 2:18 am    Post subject: Reply with quote

Nginuity wrote:
Alan wrote:
What is the voltage rating of the electrolytic cap?


The one going to the speaker? 25 volts. The others are ceramic disk.


Should not get hot... Make sure the polarity of the large cap is correct.
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Nginuity
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PostPosted: Tue Jan 16, 2007 8:33 am    Post subject: Reply with quote

Alan wrote:
Nginuity wrote:
Alan wrote:
What is the voltage rating of the electrolytic cap?


The one going to the speaker? 25 volts. The others are ceramic disk.


Should not get hot... Make sure the polarity of the large cap is correct.


Yeah, the electrolytic isnt the one getting hot. Of course, it isn't conected to ground. It's in between pin 3 and the speaker.
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Nginuity
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PostPosted: Sat Jan 20, 2007 3:59 pm    Post subject: Reply with quote

Well, I found the short....I don't know how I couldnt have seen this right away....

The two jacks that are mounted to the outside of the altoids can....Well, one of those is the other side of the + power switch from the morse code keyer. So....when power is applied across the switch, the other side is shorting to the ground bar by way of the negative on the other mono jack....

Should be an easy fix. I am either going to put a rubber grommet in there, or use some more hot glue to isolate it.
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LiesOfXIII
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Joined: 13 Dec 2006
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PostPosted: Sat Jan 20, 2007 4:39 pm    Post subject: Reply with quote

Nginuity wrote:
Well, I found the short....I don't know how I couldnt have seen this right away....

The two jacks that are mounted to the outside of the altoids can....Well, one of those is the other side of the + power switch from the morse code keyer. So....when power is applied across the switch, the other side is shorting to the ground bar by way of the negative on the other mono jack....

Should be an easy fix. I am either going to put a rubber grommet in there, or use some more hot glue to isolate it.


Just pick up some liquid electrical tape from wallmart
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