0

Sow how are they making one go 300ft plus?
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

High power DIY

by oPossum on Fri Feb 01, 2008 5:02 am

Here is a proposal for a DIY high(er) power TV-B-Gone. Several changes have been made to allow higher output.

Battery - Four AA batteries are used to allow more current to be supplied without the voltage droping too low. A pair of diodes are used to drop the 6V down to 5V for the microcontroller. They also preserve the charge stored in C2. The PCB allows for independent power supplies for the LED and microcontroller if desired.

Transistor base current - An emitter follower is used to boost the current to the base the transistors that switch LED current. The microcontoller is limited to about 20 mA (per pin). Q1 will boost this to several hundred mA. The base resistors are the same value because the voltage across them will be higher so the current will also be higher.

LED efficiency - The TSAL6100 LED is twice as efficient as the IR333 (on paper at least). There are also twice as many LEDs.

Programming Jumper - A jumper (JP2) is provided to turn off the LEDs so the microcontroller can be reliably reprogammed (via JP1) with new firmware.

NOTE: This design has not been built or tested. It is posted here for discussion.

Schematic

Image

PCB

Image
Last edited by oPossum on Wed Aug 27, 2008 7:51 pm, edited 2 times in total.
User avatar
oPossum
 
Posts: 636
Joined: Fri Oct 26, 2007 12:42 am
Location: Michigan, USA

Re: High power DIY

by caitsith2 on Fri Feb 01, 2008 6:11 am

oPossum wrote:Image


At each of the LED spots, where an X is marked, put a standard pad on the PCB, right in the center of that X. If you don't do that, then when the board goes to manufacture, there will not be any holes to properly mount the through-hole IR LEDs.
caitsith2
 
Posts: 217
Joined: Thu Jan 18, 2007 11:21 pm

Re: High power DIY

by Kova on Fri Feb 01, 2008 6:23 am

oPossum wrote:CUT

I have a simple question 8) :

Why in all schemes in this forum there isn't a Resistor in series with the LED on the Collector?

The configuration without a resistor on the Collector is (in my opinion) wrong, because the current in the LED is strongly dependent to the BETA of BJT!

All knows that the BETA parameter depends to many factors and it's change from bjt to bjt!

Than for me, the correct configuration is:
resistor to the base, emitter at gnd, resistor and led in series on the collector! :)

Sorry for my poor english ;)

P.S. Another thing: on the Atmel RST pin, it's necessary a pull up resistor (for example 10Kohm)
Kova
 
Posts: 3
Joined: Tue Jan 29, 2008 7:47 am

by jasonx on Fri Feb 01, 2008 8:30 am

WOW that is great :D
It's pretty much what I want to build but being a noob I haven't figured out how to use eagle yet :oops:
I do how ever have loads of bits like cases,components and blank pcb's on order.
Keep up the good work and let us all know when it is tested
User avatar
jasonx
 
Posts: 168
Joined: Wed Jan 16, 2008 5:41 pm
Location: england

Re: High power DIY

by oPossum on Fri Feb 01, 2008 8:52 am

caitsith2 wrote:At each of the LED spots, where an X is marked, put a standard pad on the PCB, right in the center of that X. If you don't do that, then when the board goes to manufacture, there will not be any holes to properly mount the through-hole IR LEDs.


Thanks. Fixed it. Passed ERC/DRC despite the unrouted signal!
User avatar
oPossum
 
Posts: 636
Joined: Fri Oct 26, 2007 12:42 am
Location: Michigan, USA

Re: High power DIY

by oPossum on Fri Feb 01, 2008 9:00 am

Kova wrote:I have a simple question 8) :

Why in all schemes in this forum there isn't a Resistor in series with the LED on the Collector?

The configuration without a resistor on the Collector is (in my opinion) wrong, because the current in the LED is strongly dependent to the BETA of BJT!

All knows that the BETA parameter depends to many factors and it's change from bjt to bjt!

Than for me, the correct configuration is:
resistor to the base, emitter at gnd, resistor and led in series on the collector! :)


That's a great question.

The small transistors used (2N3904, 2N4401, 2N2222, etc...) can pass a limited current (Ice Max). Their maximum current (aprox 400 to 600 mA) is a little less than a high power IR LED (aprox 500 to 1000 mA). If a larger transistor where used, then there would have to be current limiting resistors in the collector circuit to prevent damage to the LED. The internal resistance of the battery may also limit maximum LED current.

Each transistor drives it's own load (the LED), so the beta mismatch in not important. If they shared a load - like in a high power audio amplifier - then current sharing resistors in the collector or emiter circuit (depending on circuit design) would be required.
User avatar
oPossum
 
Posts: 636
Joined: Fri Oct 26, 2007 12:42 am
Location: Michigan, USA

by nutt318 on Fri Feb 01, 2008 10:12 am

oPossum,

I was wondering if these last schematics are better than the first set of schematics you posted. Just wondering which ones where better.

'EDIT' Also what kind of battery is used for battery2?
Thanks.
Last edited by nutt318 on Fri Feb 01, 2008 11:48 am, edited 1 time in total.
User avatar
nutt318
 
Posts: 65
Joined: Fri Jan 25, 2008 5:43 pm

by Probedude on Fri Feb 01, 2008 11:47 am

ladyada wrote:why do you say theres 0.2V across the transistor...? Also have you accounted for internal resistance in the 9V battery?


Better yet, what has your measurements (or Mitch's) shown for this circuit in regards to the drive current going to the IR led's for this 300' version?
Do you find the SOT-23 cased transistors are holding up okay with the power dissipation?

The small transistors used (2N3904, 2N4401, 2N2222, etc...) can pass a limited current (Ice Max). Their maximum current (aprox 400 to 600 mA) is a little less than a high power IR LED (aprox 500 to 1000 mA). If a larger transistor where used, then there would have to be current limiting resistors in the collector circuit to prevent damage to the LED. The internal resistance of the battery may also limit maximum LED current.


All true, but should circuits be designed this way? If the user uses a different battery that does have low internal resistance (NiMH or lipo) then things go poof.

Nice layout on your board, I like it. May I suggest that since you have plenty of voltage coming from the MCU to drive an FET and you use 1qty logic level N-ch FET and a dropping resistor off each LED instead. This may make layout a bit better and certainly I think it would be a more proper circuit than having a transistor driving an LED with no dropping resistor. At least the end user could then tailor the dropping resistors to battery voltage.

Here's my board using 1 FET and dropping resistors off each IR led. LED's are arranged in a 360 around the board, 12 of them.
http://www.ladyada.net/forums/viewtopic ... ght=#21321

Unfortunately I have yet to stuff it.

Dave

ps, in my last post it looks like I forgot to include the link to the other site with a high power LED powered off a 9V battery.
Here it is. Scroll down to "pulse driving the led"
http://www.rentron.com/Fire-Stick-III.htm
Probedude
 
Posts: 87
Joined: Sun Dec 23, 2007 3:16 am

by oPossum on Fri Feb 01, 2008 12:13 pm

Probedude wrote:All true, but should circuits be designed this way?

Circuits should be desinged to take advantage of the real characteristics of the components, not their ideal theoretical characteristics.

May I suggest that since you have plenty of voltage coming from the MCU to drive an FET and you use 1qty logic level N-ch FET and a dropping resistor off each LED instead. This may make layout a bit better and certainly I think it would be a more proper circuit than having a transistor driving an LED with no dropping resistor.


A FET will only have a low Rds up to a certain Ids (for a given Vgs). Beyond that it will limit current (and get hot). Look at the spec sheet for a 2N7000 FET. It is much less capable than a 2N4401 bipolar, but several times the price. Using a power MOSFET would allow current setting with a series resistor. I did that a while ago.

Bipolars are more rugged than (MOS)FETs and more readily available. Almost any small signal NPN will work in that circuit. A FET would have to be carefully selected for Vgs and Ids. Think about who might build this and where they source their parts.

Here's my board using 1 FET and dropping resistors off each IR led. LED's are arranged in a 360 around the board, 12 of them.


What is the part # of the FETs that you used?
Last edited by oPossum on Fri Feb 01, 2008 2:03 pm, edited 1 time in total.
User avatar
oPossum
 
Posts: 636
Joined: Fri Oct 26, 2007 12:42 am
Location: Michigan, USA

by oPossum on Fri Feb 01, 2008 12:33 pm

nutt318 wrote:oPossum,

I was wondering if these last schematics are better than the first set of schematics you posted. Just wondering which ones where better.

'EDIT' Also what kind of battery is used for battery2?
Thanks.


Better in what way? The first schematic (provided by Mitch Altman) is of a retail product that you can buy. The second is for DIY.

I can't say for sure what one has more IR power output. I think the DIY EHP version will have about double the retail SHP version.

The second battery is optional. D1 and D2 would not be installed if two batteries are used. The LEDs can then be powered by one battery and the microcontroller by another. The advatage of using two batteries is that the microcontroller is completely protected from the voltage drop that occurs when the LEDs turn on.
User avatar
oPossum
 
Posts: 636
Joined: Fri Oct 26, 2007 12:42 am
Location: Michigan, USA

by nutt318 on Fri Feb 01, 2008 12:43 pm

oPossum wrote:The second battery is optional. D1 and D2 would not be installed if two batteries are used. The LEDs can then be powered by one battery and the microcontroller by another. The advatage of using two batteries is that the microcontroller is completely protected from the voltage drop that occurs when the LEDs turn on.


Ok, I think that makes sense to me. If you wanted to used the second battery what would you recommend using for it for it? Type of battery and how many?
User avatar
nutt318
 
Posts: 65
Joined: Fri Jan 25, 2008 5:43 pm

by Probedude on Fri Feb 01, 2008 1:10 pm

oPossum wrote:What is the part # of the FETs that you used?


FDS6690A in the SOIC-8 package since this is what I had laying around.
$0.80 each in 1 piece qty from Digikey.

datasheet is here
http://www.fairchildsemi.com/ds/FD/FDS6690A.pdf
Probedude
 
Posts: 87
Joined: Sun Dec 23, 2007 3:16 am

by nutt318 on Mon Feb 04, 2008 10:35 am

oPossum wrote:The second battery is optional. D1 and D2 would not be installed if two batteries are used. The LEDs can then be powered by one battery and the microcontroller by another. The advatage of using two batteries is that the microcontroller is completely protected from the voltage drop that occurs when the LEDs turn on.


If the second battery is used why type of battery would be needed?
User avatar
nutt318
 
Posts: 65
Joined: Fri Jan 25, 2008 5:43 pm

by cubistuterus on Wed Feb 06, 2008 10:19 pm

if we're going to overload these LEDs we'll need to edit the firmware also. as it stands, some of the power codes turn the LEDs on for 25ms, which is fine at 100mA, but at 1A they need a 5% duty cycle of no more than 1ms/pulse! the specs on the eyebright led are even more stringent, so I assume the tvbgonepro is doing something of the kind. eyeballing the 6100 datasheet it seems that we could get away with 10% duty at 800mA and 10us.

does the ATTiny85 have PWM? that might be a quick solution...
cubistuterus
 
Posts: 6
Joined: Thu Jan 31, 2008 9:35 pm
Location: Devon, UK

by nutt318 on Thu Feb 07, 2008 2:01 pm

cubistuterus wrote:if we're going to overload these LEDs we'll need to edit the firmware also. as it stands, some of the power codes turn the LEDs on for 25ms, which is fine at 100mA, but at 1A they need a 5% duty cycle of no more than 1ms/pulse! the specs on the eyebright led are even more stringent, so I assume the tvbgonepro is doing something of the kind. eyeballing the 6100 datasheet it seems that we could get away with 10% duty at 800mA and 10us.

does the ATTiny85 have PWM? that might be a quick solution...



I also would like to know about this, I am putting one together on a breadboard and dont want to fry my 6100's.
User avatar
nutt318
 
Posts: 65
Joined: Fri Jan 25, 2008 5:43 pm

Please be positive and constructive with your questions and comments.