Problems with TV-B-Gone

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LostTime
 
Posts: 43
Joined: Sat Mar 08, 2008 9:14 am

Post by LostTime »

Probedude wrote:Boy I'm confused as to what could be the problem. You mentioned you have an oscilloscope.

- what does th signal look like coming out of the Atmel when it is hooked up to the 47 ohm resistor to the base of your NPN transistor?
- what is the part number of your NPN transistors?

Thanks,
Dave
It's easy to describe what you can see on the oscilloscope's screen:
Nothing!
Not a single peak comes out of the MCU...
When I test the MCU only, without the transitors, the signal l0ooks normally...

The transistors are 2N3904, as listed in the parts list an they're working...

Sebastian

Probedude
 
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Joined: Sun Dec 23, 2007 3:16 am

Post by Probedude »

Just to try, can you replace the 47 ohms resistors from the output of your ATMEL to the transistors with 4.7K resistors and then tell me what you see coming out of your Atmel on the oscilloscope?

LostTime
 
Posts: 43
Joined: Sat Mar 08, 2008 9:14 am

Post by LostTime »

Probedude, actually something has changed!
With the 47 resistors the green LED blinked like this:
long - 4 times short - 5 times short - long

Now its
long - 4 times short - 5 times short - long - short - short - short - ...

And the output of the transistors have also changed.
To GND and the transistor output are 3V or 2.5V, wild changig..
The IR-LEDs are blinking!!

Thank you, thank you, thank you!!!

*jumping around*
I'll now test it with my TVs..
:D :D :D :D :D

LostTime
 
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Joined: Sat Mar 08, 2008 9:14 am

Post by LostTime »

YES!!!
It's working.. I'm able to switch our TVs off (2 KENDO and a Medion)..
Great!

Probedude
 
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Joined: Sun Dec 23, 2007 3:16 am

Post by Probedude »

LostTime wrote:YES!!!
It's working.. I'm able to switch our TVs off (2 KENDO and a Medion)..
Great!
Great, but now this just means that your problem has been pinpointed.
- increasing the values of these resistors reduces the amount of current being pumped into your IR LED's. So their optical output too will be reduced and therefore your range.

- The lower drive current going to the IR LED's could mean that the supply voltage to your Atmel chip is now no longer drooping causing it to reset.
- Or your 47 ohm resistors are not really 47 ohms
- Or you need more capacitance on your atmel to keep the voltage up
- or your batteries are not able to maintain voltage under load.

So it works but now you need to figure out why it didn't before :)

Can you put the 47 ohm resistors back but use 3 AA's in series instead? This will keep your voltage up for the Atmel chip.

Dave

LostTime
 
Posts: 43
Joined: Sat Mar 08, 2008 9:14 am

Post by LostTime »

Difficult..
Because than the copper of the PCB will come off...

And my housing is too small for 3 AAAs, but maybe I'll make a second, bigger version

By the way.. thats my TV-B-Gone:
http://losti.kisslab.de/gallery2/v/elek ... 5.jpg.html

Wherzog
 
Posts: 5
Joined: Sat Mar 08, 2008 6:08 pm

It is the battery

Post by Wherzog »

Looking at your pictures I have to say that this battery is definitively NOT able to drive the LED with maximum current.

The data sheet says it is a buffer batterie for CMOS memory. Maxium current is 50mA! This battery is optimized for low self discharge and long lifetime, not for high current.

I think this is the reason for your technical problems... 8)

Go for two AAA - they should fit into your housing

LostTime
 
Posts: 43
Joined: Sat Mar 08, 2008 9:14 am

Post by LostTime »

The yery first version of my version was powered by two AAA, but it had no effect.
Maybe I can scape up a battery for tanks or submarines :wink:

magician13134
 
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Joined: Wed Jun 13, 2007 9:17 am

Post by magician13134 »

I was thinking three AAAs, they look like they'd fit.

LostTime
 
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Joined: Sat Mar 08, 2008 9:14 am

Post by LostTime »

magician13134 wrote:I was thinking three AAAs, they look like they'd fit.
Sorry, they won't fit..
Okay, there's a lot of space beneath the PCB, but this space is used by the pushbutton, too.
By browsing through a catalog of a German electrical retailer, I've found something like this:
GP Remote Control Battery

I think this battery is made for high-current applications and it's much cheaper than the backup-battery (1.00€ vs. 5.00€).

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opossum
 
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Joined: Fri Oct 26, 2007 12:42 am

Post by opossum »

That battery is for RF remotes, not IR remotes. It can not supply much current.

A CR123 or CR123A battery would be the best small 3V battery. It can provide as much current as 2 x AAA.

LostTime
 
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Joined: Sat Mar 08, 2008 9:14 am

Post by LostTime »

Damn.. But thanks oPossum, I'll try it

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