shadow wrote:Probledude- srry about the LED shortage
if your in Phoenix, Arizona, i could spare some extra
woody1189 wrote:just experimenting with the chip design some more...i noticed some problems with 4 leds off of 3 fresh alkalines in that the codes wouldn't cycle. i dont think the alkalines can supply enough current for 4 emitters but when you use just 2 leds it blasts em. lost 3 tsal6100s in the process :(
woody1189 wrote:i was using a multimeter but then i realized that those readings were most likely wrong. i was hoping to at least see some spikes above 100ma but all i got were low readings. i'm gonna test it on a scope once i go back to school next week.
Probedude wrote:Ended up frying 6 of my LED's - the symptom was no IR output. They were working for a bit, then not.
The official SHP TV-B-Gone is using 10 ohm base resistors - so I did too, but I was using PN2222A vs 2N4401 transistors. I changed the 10 ohm resistors out for 47 ohm, replaced all the IR LED's (again with Everlight - my TSAL order hasn't arrived yet). Activated it 3 times and it's still working.
Transistors still get pretty hot though! Would not want to use sot-23 sized smt parts with this much power.
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.
I think you are very optimistic about the internal resistance of Li- batteries.
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.
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 measurementsI agree that sot-23 would not tolerate the current, but sot-223 would probably be OK.
woody1189 wrote:probedude, wire one of these up to your lipo pack and you wont have discharge or overcharge problems.
http://www.batteryspace.com/index.asp?P ... rodID=2774
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