I'm working on building an IR blaster / receiver setup. Using an ATTiny85 on the blaster side.
I'd like to kindly request some help/review regarding my attached schematic.
For the IR LEDs, I am using Vishay TSAL5100 LEDs.
Since this is for outdoor use, I'd like to run them at 1A power or at least very close to it. At 1A, their forward current is 2.6V.
The whole circuit will run on 5V.
Various questions:
- Do I need anything else, other than what's shown in the schematic?
- Do the resistor values look right and do I even need the 1 Ohm resistors?
- Is 1 transistor toggling both "banks" of LEDs enough or should I use two transistors in parallel?
The LEDs will emit bursts of 38Khz pulses.
Thanks for your help!
There is a very good forum called Miles tag which is all about laser tag & they have documented in their forum/website all you need to know about pushing IR Leds to the max.
I believe the TSAL6100 is the preferred for long-range and narrower beam. But they also use one from another supplier which can be driven up to 2 amps(?).But the IR output at this level may be outside safety levels for Humans.
It is also possible to increase range using optics.
You also need to consider duty cycle and pulse durations if you are pushing the limits like this.
Would you care to share the your specific application?
I would think designing with one resistor in series with each LED is the best way to go, particularly if one LED blows you will lose the second also, as per your circuit.
Once you decide on your best approach you then need to calculate the values for base resistor & current limiting resistors based on the specs of the IR LED & transistor being used. There are calculators to do this online.
If you total all your voltage drops of the 2 LEDs plus the transistor, you will notice it is greater than 5V, plus you will also drop another 1V over a 1ohm resistor @1A
PS if you're planning to drive 1A thru 4 IR LEDs, make sure you look into the safety aspect for eyes!
Thanks for the info. I will check out that forum.
The specific application here is a race car timing system. This blaster and a receiver on the other side will form a light barrier which will be disrupted by cars going through at high speed.
The distance between the emitter & receiver will be around 10 meters, but outside in bright sunlight...
You should be OK with 1 LED for that application/distance running at less than .5A, but would benefit immensely by using a single lens to focus the beam. The extra LEDS & power could cause you more problems. Or even just a long narrow tube to put the transmitter into. make sure the receiver is facing away from the sun. TSAL6100 is the best option for you with a narrower beam.
The best IR receiver for this application is TSSP58038 from Vishay.
However, a laser beam into a photo cell would be a much much better solution.
You could also just use a reflector on the far side, which would mean you could have both the IR LED & Receiver in the same enclosure
AnalysIR:
You should be OK with 1 LED for that application/distance running at less than .5A, but would benefit immensely by using a single lens to focus the beam. The extra LEDS & power could cause you more problems. Or even just a long narrow tube to put the transmitter into. make sure the receiver is facing away from the sun. TSAL6100 is the best option for you with a narrower beam.
Preliminary tests with 1 LED that I've done outdoors showed that the signal got unreliable at about 4-5m.
Though I will do some more research. I've checked out the laser tag forums and, as you said, it seems like 1 LED + lens is probably all I need.
The best IR receiver for this application is TSSP58038 from Vishay.
Hmmm, I'm using the TSOP4038 right now. Will have to look to see what the differences are.
Maybe all I need is a better receiver as well...
However, a laser beam into a photo cell would be a much much better solution.
I have used laser based timing systems and have not been convinced. They are harder to aim and require more battery. Since this is for portable track setups, it's harder on the staff to have to aim a exactly and battery life can be an issue.
You could also just use a reflector on the far side, which would mean you could have both the IR LED & Receiver in the same enclosure
That would be a nice setup. But that will double the distance of course and also cause more aiming issues.
We had a laser + mirror setup as well and that was the worst as far as aiming the beam goes 
Maybe IR + reflector would be less touchy, but I think I'd still prefer a sender/receiver setup.
Thanks for your great help so far by the way, really appreciated!!
Please keep the advice coming!
Just looked at TSAL6100 vs TSAL5100 and it seems that the only difference is the metal pins & otherwise they should be identical...so thats good news.
The 4-5m could well be related to the IR receiver as well. Do you know how much current you were pushing thru the LED? A standard TV remote should get more than that range outdoors.
The TSSP58038 receiver is designed to be a presence sensor or beam break detector. Normal TV remote receivers have AGC logic that may cut out constant signals. So getting the TSSP58038 receiver should double your range and more.
If you are running at 100mA+, battery may be an issue with IR as well.
Another trick I have used in the past is to pulse the IR signal eg 500uSecs on & 500uSecs off and measure that at the receiver. This can seriously help outdoors with solar interference and effectively gives a much longer range & half the battery drain. You will of course have to factor in the impact on timing accuracy. If you have to wait up to 500 uSecs before a detection vs 13 uSecs with modulated IR.
I havent played much with lasers, but I presume you could pulse it in such a way as to reduce battery consumption(?)
The thing about a good reflector approach is that it essentially only reflects a small beam.
Also bear in mind that if you flood the place with IR you could get reflections from almost anywhere, particularly shiny surfaces. (rainy day...)
Ok, new schematic with just 1 LED attached.
A 3.3 Ohm resistor will put me right around 750mA.
Maybe a little less since the turn-on time of the LED seems to go up depending on the power. Maybe I'll settle on 500mA
I will definitely send pulses around 250us.
Let's know how you get on with an outdoor test.
Remember if you are pulsing at 250 uSecs on & 250 uSecs off and your modulation duty cycle is the typical 50%, then your 750 mA turns into an average/effective 187mA (or 125mA instead of 500mA).
(unless you have already taken this averaging into account)
How did you measure the current flow or is it just a calculation?
The most I have driven them is 200mA which averaged out to 50mA, as I didn't need very long ranges, but you should be fine with the 500mA as long as you have some spares.
FWIW, Photocells are not great for this kind of purpose; they take too long to react to the beam break. You can pretty easily swing your arm through a laser/photocell beam and not have it detected and I would bet you could run through one as well.
With respect to using lasers, if you get a focusable laser (which aren't hard to find) then you can widen the dot so it's not an aiming challenge. Also, they'll handle a 38KHz modulation just fine. You can find them in batches on eBay for a couple bucks a piece.
With respect to using a 3.3ohm resistor with the LED, whenever you calculate a solution where the resistor is less than ~47R you've got a situation where the current regulation will not be appropriately accurate when you take into account how the forward voltage will vary from LED to LED. The TSAL5100 reports a typical Vf of 1.35V but it can be as high as 1.6V -- you should run your calculations with at least a .2V leeway. Also, I can't imagine it would be reliable to run these at more than 100ma; the 1A rating is only for a single, 100 microsecond burst.
Last tip, make sure the IR receiver is well shielded from sunlight. In my case I placed the IR receiver at the back end of a 6" long piece of 3/4" PVC to keep it shielded from light. Also makes its reception more directional.
AnalysIR:
The TSSP58038 receiver is designed to be a presence sensor or beam break detector... So getting the TSSP58038 receiver should double your range and more.
TSOP4038 (which is the earlier model TSSP4038) is the same as TSSP58038 with a slightly smaller package.
AnalysIR:
Normal TV remote receivers have AGC logic that may cut out constant signals.
Vishay's docs are quite clear that receivers designed for remote controls will reject constant signals and specifically state the maximum length of bursts and required "off" time. Try http://www.vishay.com/docs/82491/tsop382.pdf and see page 5 for an example. Not that I mean to jump on you for that but I saw your earlier discussion with Mike and thought I'd clarify.
@Chagrin - thanks for the update
TSOP4038 (which is the earlier model TSSP4038) is the same as TSSP58038 with a slightly smaller package.
TSOP4038 - good spot, they are indeed replaced by the TSSP4038, which is what threw me, as most of the TSOP ones seem to be for CIR purposes nowadays. So the OP should be good with the TSOP4038 and migrate to TSSP4038 or TSSP58038 in future. The TSSP58038 may have a better Horizontal & vertical Directivity for this type of application (= batter range) than the other 2. If you look at the datasheet, it may even be beneficial to tilt the TSSP58038 forward a wee bit. (untested)
Regarding the continuous signal....The data sheet for TSOP4038, TSSP4038, TSSP58038 says:
on page 1 - It can receive continuous 38 kHz signals or 38 kHz bursts
I think the data sheet you referenced in the link is for a different model.
+1 on the tubing...a second one could also be used to mount a lens on the Tx side
Regarding the TSAL5100, I believe the forward voltage can go to 2.6V ->3V from 1A+, which is why measuring would be important. Probably wouldn't want the LED to burn out in the middle of an event
