For my son’s 6th birthday in just over a month, we’re doing a circus themed multi-station party for him and his friends. I’m wanting to setup a soldering station for the kids to build their own “badge”. The idea I’ve been working with is to have each badge be able to send and receive IR. When IR is detected then an LED is illuminated. The idea being that it can act as a game where as the kids get closer to each other their badges will start flashing (because the IR is transmitted in pulses). I’ve got the attached circuit working well as long as the badges are within 6-8" of each other. I’d like them work from about 3’ away. From a couple feet away, I can see a faint flicker of light in the LED, so I know the IR is being detected. Any ideas on how to encourage it to consume more current?
Because these are basically disposable and I’ll probably order 50 PCBs, cost is of the greatest concern. So, I really don’t want to over complicate this by adding a uC or other expensive parts that can’t be acquired in bulk off eBay if possible. I’m open to all ideas at this point though. Any leftovers will probably be used for soldering lessons in our microcontrollers users’ group.
NOTE: The part labeled “PHOTOTRANSISTOR” is a phototransistor (IR detector + NPN transistor) although it’s part looks like an LED. If anyone knows where the appropriate part in Eagle is for a 2-wire 5mm shaped phototransistor, please let me know. The other 2N222A in that subcircuit is there to make a Darlington pair to increase the sensitivity.
Also, does anyone know how to make an Ohm symbol in Eagle?
Any other ideas on how to make this badge even more fun are certainly appreciated.
@ godefroi - did you read my “NOTE:”? Perhaps I’ll try adding a third transistor to the mix. I may open it to the point that every little piece of stray light sets if off…
@ devhammer - I don’t think it’s a transmission issue since I’ve done most of my testing using the remote from my IR Receiver module. One problem I do have on the transmitter side is that the beam seems too narrow. I have to have the LEDs in fairly direct line of sight before anything substantial happens. These are my IR LEDs. I believe they would be considered narrow beam.
I added a second external transistor and it did help quite a bit. Hopefully, it didn’t help too much. I only have a clear phototransistor at the moment and even under my desk it’s hard to keep it from picking up too much stray light. I have dark phototransistors on the way. Hopefully that will solve the problem.
@ devhammer - I really hadn’t paid much attention to the transmitter side of things since I was using a remote as my transmitter for testing. I dropped R1 & R4 down to 56 Ohms and they seem acceptable. I’m going to play with R2 & R3 now and try and get my frequency down to 2 or 3 Hz… According to the multivibrator freq formula (f = .721/RC), I should need something in the 36K Ohm range but it doesn’t appear now that I’m getting flashing, just solid light. I must have crossed something up while moving things around
I don’t know what the current gain on a phototransistor is, so I don’t know what gain a darlington pair using one would result in. You could probably desensitize the phototransistor a bit with another resistor.
Not sure whether it’d be worth the additional cost, but a trim pot would make it possible to tweak the sensitivity after the board is assembled. Might be worthwhile on a prototype at least, so you can dial in the right value.
Their radiant intensity is only 20 mW/sr, and it definitely showed in my results.
Now interestingly enough, looking back at the specs, it may well be that it’s not a matter of beam angle (or viewing angle, as the specs of the two LEDs use differing terminology), since it appears that the one I’m using may actually have the wider angle, so perhaps I missed something in my original parts sourcing. But the radiant intensity certainly makes a difference for me, and the first link is far more intense.
The parts at Mouser are a bit more expensive, but the difference between 10 cents a pop and 16 cents a pop isn’t a big deal at the quantity we’re talking about.
Might be worth ordering a few to see if perhaps it’s your LEDs that are slowing you down.
I’ve settled on this design which is working satisfactorily. Now, I’m trying to source the parts. I want to use SMD components for the capacitors because they are going to be mounted opposite the battery on the other side of the PCB. Finding electrolytic 22uF capacitors in SMD like I used in my prototype has turned into a bit of a challenge. The ones I found at Digikey are over $1 each in low quantities. I’ve found some very good deals on SMD tantalum capacitors. Could these be used to replace the electrolytic versions in this design or is it essential that they are polarized?
I think I’m ready to send this thing off but I’d like you guys to give it a quick glance over first since I probably only have time to order one batch before the birthday party. Any and all criticisms are welcome. Yea…I know it turned out a little creepy but artistry isn’t one of my specialties… The idea is that I will have this made on red PCB and it will end up looking like a clown mouth (it’s a circus themed party). The big white area on top is for them to write their name in. The 6 year olds will only be soldering the resistors. I’ll do the more delicate parts in advance.
The Eagle files can be found here if you prefer to look at it natively.
Big thanks to godefroi for screening it already and saving me from complete embarrassment!
Thanks, guys! There will definitely be pics & videos if all turns out well.
Next question… I decided to send off the Gerber files to BatchPCB for a quote and to try out their testing. It failed on top copper and I’m not sure why. Does anyone have experience reading their error reports? How would you interpret this?
[quote]unmatched 274X paramblock OFA0B0 - len 6
Macro Name = OC8
Macro Consuming 5,1,8,0,0,1.08239X$1,22.5 
Looking up macro OC8 [0x2259190]
Beginning GCODE run
Ending GCODE run
Created 313 polygons
Found 0 errors
Board boundaries: Rect: [0.002000,0.002300] -> [3.356700,1.691500], w: 3.354700, h: 1.689200
Found 25 groups
lengthdb size 0
exit status: 0
DRC put out 27 lines of logging code
Also, it looks like SeeedStudio is on another one of their Chinese holidays until Oct 7th. Any other ideas on where I can get red PCBs at a similar rate as Seeed?
I’m ordering the PCBs tonight from DFRobot.com. It’s working really well. The line-of-site has to be a little more direct than I had originally hoped for but it should make for some interesting photos as the kids discuss in Borg fashion their badges After building these, I’m amazed that IR remotes work at all.