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Sow how are they making one go 300ft plus?
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Sow how are they making one go 300ft plus?

by nutt318 on Wed Jan 30, 2008 11:32 am

I was looking at the original tv-b-gone website and noticed that they are accepting pre-orders for the SHP model. Only 40 bucks for all US and Eroupe codes and its in a PDA case

https://www.tvbgone.com/cfe_tvbg_buy.tv ... f160a0bff5

So how are they getting the 300ft plus and how can we make one?

Anyone know?
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by oPossum on Wed Jan 30, 2008 12:41 pm

Schematic: Page 1 Page 2
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by nutt318 on Wed Jan 30, 2008 1:11 pm

oPossum, Wow, thanks for the schematics. I wish I knew how to read these better. Is there a parts list for this one like the older version?
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by TheDon125 on Wed Jan 30, 2008 1:52 pm

Is it just me, or are the high power LEDs used in the newer tv-b-gone the same as those used in the tv-b-gone kit here? Any ideas how 3x the range was achieved? Appears as though the resistors on the LEDs have been dropped from 47 ohms to 10 ohms.
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by Probedude on Wed Jan 30, 2008 3:21 pm

More importantly you'll see that the base of the transistors driving the LED's is NOT driven directly by the microcontroller unlike the Adafruit version but instead by using another transistor.

I don't know what the drive capability of the Atmel controller is but likely ~ 25mA. Using the transistor in between it can drive the emitter transistors much much harder.
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by nutt318 on Wed Jan 30, 2008 6:27 pm

On the schematics of this new version what kind of microprocessor is it using, an Atmel?
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by mtbf0 on Thu Jan 31, 2008 12:12 am

seems to be a zilog z8 variant designed for use in ir applications.
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by Probedude on Thu Jan 31, 2008 12:31 am

I just noticed too that they're driving the IR led's directly off a 9V battery.
Seems excessive considering there is no dropping resistor to the IR LED's.
Wonder if they measured the current flowing into the LED's.
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by TheDon125 on Thu Jan 31, 2008 2:59 am

I ran it through one of those online LED calculator things, and figuring a fresh 9V and a 0.2V drop across the transistor, there is about 900mA flowing through those LEDs.
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by nutt318 on Thu Jan 31, 2008 10:11 am

TheDon125 wrote:I ran it through one of those online LED calculator things, and figuring a fresh 9V and a 0.2V drop across the transistor, there is about 900mA flowing through those LEDs.


Is that alot compared to the older version?


Also on a side thought, Could anyone put the schematic into lamings terms. I cannot read schematics at all but just a little and was wondering if someone could bu the actual part number or description for each item.
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by Probedude on Thu Jan 31, 2008 3:24 pm

TheDon125 wrote:I ran it through one of those online LED calculator things, and figuring a fresh 9V and a 0.2V drop across the transistor, there is about 900mA flowing through those LEDs.


Can you post the URL? That calculation doesn't look correct to me.


Here's a link to some calcs done with a similar drive setup (9V being used to switch an IR) with the exception that a darlington was used. Scroll down to the "pulse driving the LED" section.

Dave

Sorry! Looks like I forgot to include the link.
http://www.rentron.com/Fire-Stick-III.htm
Last edited by Probedude on Fri Feb 01, 2008 11:48 am, edited 1 time in total.
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by nutt318 on Thu Jan 31, 2008 3:36 pm

Link?
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by salsaman on Thu Jan 31, 2008 4:17 pm

Thanks, 'possum!
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by adafruit on Thu Jan 31, 2008 5:25 pm

TheDon125 wrote:I ran it through one of those online LED calculator things, and figuring a fresh 9V and a 0.2V drop across the transistor, there is about 900mA flowing through those LEDs.


why do you say theres 0.2V across the transistor...? Also have you accounted for internal resistance in the 9V battery?
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by TheDon125 on Fri Feb 01, 2008 3:49 am

When I said the 0.2V across the transistor, I meant the voltage drop caused by the transistor (which looking at the datasheet is more between 0.4V and 0.75V, depending on the current flowing through the transistor). And no, I forgot about the internal resistance of the 9V, so my number is probably very off (the transistor itself is only rated for 600mA max)
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