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Nginuity
HG Ruler
Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas
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 Posted: Sun Jan 14, 2007 2:16 pm Post subject: Altoids can Morse Code Oscillator |
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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
HG Master
Joined: 30 Apr 2006
Posts: 134
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| Posted: Sun Jan 14, 2007 7:01 pm Post subject: |
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| Looks nice. Much cleaner than the stuff I make. |
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Nginuity
HG Ruler
Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas
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| Posted: Sun Jan 14, 2007 7:21 pm Post subject: |
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| 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
HG Master
Joined: 30 Apr 2006
Posts: 134
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| Posted: Sun Jan 14, 2007 10:04 pm Post subject: |
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| 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
HG Ruler
Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas
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| Posted: Sun Jan 14, 2007 10:12 pm Post subject: |
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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 
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
Site Admin
Joined: 29 Jan 2006
Posts: 1340
Location: Winnipeg, MB
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| Posted: Sun Jan 14, 2007 10:15 pm Post subject: |
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| 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! 
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
HG Ruler
Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas
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| Posted: Sun Jan 14, 2007 10:35 pm Post subject: |
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| Alan wrote: | Nice job, the finished project looks very nice!
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
Site Admin
Joined: 29 Jan 2006
Posts: 1340
Location: Winnipeg, MB
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| Posted: Sun Jan 14, 2007 10:39 pm Post subject: |
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| What is the voltage rating of the electrolytic cap? |
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Nginuity
HG Ruler
Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas
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| Posted: Sun Jan 14, 2007 10:41 pm Post subject: |
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| 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
HG Ruler
Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas
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| Posted: Sun Jan 14, 2007 10:44 pm Post subject: |
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| Nginuity wrote: |
C2 is 4.7 uf
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Sorry, correction, C2 is .047 uf, not 4.7 |
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J0ker
Newbie
Joined: 15 Jan 2007
Posts: 1
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| Posted: Mon Jan 15, 2007 11:09 pm Post subject: |
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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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Alan
Site Admin
Joined: 29 Jan 2006
Posts: 1340
Location: Winnipeg, MB
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| Posted: Tue Jan 16, 2007 2:18 am Post subject: |
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| 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
HG Ruler
Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas
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| Posted: Tue Jan 16, 2007 8:33 am Post subject: |
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| 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
HG Ruler
Joined: 13 Nov 2006
Posts: 224
Location: Dallas, Texas
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| Posted: Sat Jan 20, 2007 3:59 pm Post subject: |
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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
HG Supreme
Joined: 13 Dec 2006
Posts: 62
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| Posted: Sat Jan 20, 2007 4:39 pm Post subject: |
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| 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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