oPossum wrote:Go higher on the base resistors, not lower. Mitch's SHP has a 9V battery with a very high internal resistance, so there is no need to limit LED current by any other means. The EHP design assumed AA alkaline batteryies, so peak current was somewhat of a concern, but not a big one. The battery you are using can easily fry the LEDs if the AVR voltage drops too low. The base resistors should be increased to limit the LED current and reduce the battery voltage drop.
Which is why I went from 10 ohms from Mitch's design (which burned out the LEDs) to 47 ohms, not the other way around. I fried the LEDs using the 2 lipo cell setup with a LDO regulator feeding the MCU and a cap. No worries about dipping voltage and it didn't fry the LEDs because the MCU didn't have enough voltage.
I think you are very optimistic about the internal resistance of Li- batteries.
Where's the optimism? All the other TV-B-Gone designs have been powered by alkaline AA, AAA or 9V batts. This particular lipo pack is rated for 20C continuous discharge - it's not a cell phone lipo and the IR is much better than a series string of the above batts.
I don't see a diode on your PCB. It would be a good idea the have a Schottky diode between the battery and the AVR, and a 100 uF cap in parallel with the AVR. That will provide some protection against voltage drop during the high current pulses.
Agreed for other setups - but not an issue with my 2 lipo setup (see above). My 1 lipo cell setup doesn't have an issue either. The bigger concern is to make sure I don't overdischarge the lipos.
I agree that sot-23 would not tolerate the current, but sot-223 would probably be OK.
Likely better - power dissipation values for the sot-223 package on a properly designed PCB if I remember correctly is better than the to-92 case. Downside is the pcb footprint is larger on the sot-223 vs the to-92. Going back to Mitch's SHP schematic he shows sot-23 transistors being used. It works because of the 9V battery. It won't work with a full charged 2 cell lipo (8.4V) though if anyone else follows my footsteps and uses the SHP schematic verbatim. That's what I get for not taking measurements :)
Last night I did some range testing. Very good distance inside the house, ~ 70' - down the hall and around a corner I can nail my TV no problem. Could only do half the hall distance before.
From outside my house standing on the porch, pointed through the closed front door security window, around a corner to the TV in another room - success!
Went into Best Buy and Sam's club - turned off a few TV's for as little time as I wanted to spend standing in one spot facing that direction. For some reason my success was zero at Walmart. Had this problem before too. Don't know why - wonder if they tape over the IR receivers on their wall of TV's.
Tonight I think I'll take the dogs for a walk and see if I can turn off neighbor TV's from the sidewalk pointed toward their living room/ bedroom windows.
edit: Just bought a dummy Blackberry phone on Ebay. TVBG EHP with 2 cell lipo in a Blackberry Pearl! Woohoo!