'Throwie' Style TV-B-Gone

[Teslacuted]

Hi guys,

I'm thinking of a small project to take the existing TV-B-Gone kit and remove as many parts as possible to get it down to the size of an LED throwie. (using a single wide angle, 160degrees maybe)

I'm not particularly experienced with practical circuits so I was hoping if I listed my ideas someone might be able to say 'that'll never work' to some of them.

The ATTiny85V is able to provide 10mA per IO pin (and sink 40mA) according to the datasheet (page 166, unless I've misread it, which is very likely). According to some of the register controls its possible to bring two pins high on the same clock cycle, could one IR led be powered solely from these pins? Either by providing 20mA or sinking 80mA? This would remove the need for the resistor and the NPN.

How much current do the LEDs suck anyway?

We'll use software control instead of a physical switch, so that's another part saving/IO pin to use.
No need for the programming header as its a one-shot device.
Which leaves the AC shunts and the oscillator...

I bought some CR2032 3V cells, ideally I'd like to power the thing from a single cell but I don't know if these little cells can support the drain -- can anyone comment?

Are the shunts absolutely needed? With a single LED the drain will be much less than the 4 LED model and from what I understand about batteries the shunts get more important as the battery ages, but longevity isn't really a concern with this.
Lastly, can I do away with the external ceramic and use the inbuilt oscillator? What sort of problems would this lead to?

Thanks in advance for any support,
Hugh

[adafruit]

to get any good range you need to put about 100-500 mA PER LED

[Teslacuted]

That's a bit more than I thought, do you think that completely rules out a single coin cell? Or can I stick in a buffering capacitor presuming the duty cycle of the LEDs isn't too high?

Big fan of your work by the way


Edit: Looks like the internal oscillator can be calibrated to bring it from +/- 10% down to +/- 1%, so that particular component saving should work.

[adafruit]

you could use one of the 1" diameter coin cells
or a lithium polymer battery
AAA's are cheaper

[Teslacuted]

Just did a quick test and a 2025 is actually fully capable of lighting an IR LED, I have no way to measure the lumens (is that the right measurement?) but it blinded the CCD on my phone so I'm reasonably pleased. VDiff on the cell was 1.7V though which only leaves 1.3 for the AVR, 0.5V below its rated minimum. I'm going to experiment a little more and see if pulsing it rather than the full-on test I did keeps the Vcc higher. If I put two cells in parallel would it help keep the Vcc up or would the LED just burn the extra current that's available? (there's no resistor in use).

[adafruit]

i think you should spend a couple more days experimenting

[Teslacuted]

Indeed, why rush the fun? No one's said 'that'll never work' yet so a 3 component "oops, did I leave that in the TV shop" TV-B-Gone might just be a possibility.

[richms]

Bonus points if you can conceal it into something that should be in the shop like part of a display stand etc.

[Penfold]

You could always use the less known about "quadruple A" batteries you can get from cracking open a 9V battery. I believe there are six per battery.

What do you think Ladyada?

[adafruit]

i dunno. what happens when you try it?

[furrtek]

I had to quickly build one a five days ago. It's only meant to send three codes every 15 minutes so I used a Tiny13
There's a BC547, a cheap (but nice) 60° 940nm IR led, a cube neodymium magnet, a CR2032 lithium cell and a 6-pin ISP connector.
Checked today: it still works.

[richms]

hehe nice...

What do you think the cost of those would be all up?

More myschivious would be to have a library of off codes and other assorted ones like teletext and change input and have it chuck them out randomly. perhaps a burst of volume up or down occasionally as well for good measure

I dont know about there, but here if it did samsung, sony and panasonic you would hit 90% of displays. philips stopped selling here a year or two back and because they were all banned they have blown up and stopped working now, and the rest are the odd bit of off brand junk that you would have minimal chance of getting.