I got the USB IR Toy v3 as a free PCB from Dangerous Prototypes a few weeks back, but until recently I haven’t had much time to track down all the parts for it. Given that this is a v3 and not a v2, there isn’t a simple shopping cart of parts at Mouser kicking around. So, I decided to make one! Here is the link to the project on Mouser. I have some notes from assembling it, though, that someone with more knowledge of the project should hopefully be able to respond to.
- I didn’t specify an inductor for L1, my plan is to simply short the pads together. My logic is that I have no idea where to find an 0805 footprint inductor, and the bypass caps on all the ICs should be plenty. Yes? No?
- I decided to use one of the already-required 1µF ceramic caps for the regulator, rather than a polarized cap as none was specified. The bigger footprint suggests a tantalum was intended, but the datasheet for the regulator makes no specification as to WHAT kind of bypass cap should be used, only that it should be >=1µF. And the 0805 cap used elsewhere in the project will physically fit those pads.
- VUSB of the PIC is shorted to 3v3 = VDD, is that right? It seems to me like it’s not, but then maybe it’s a typo in the schematic symbol for the IC.
- PIC18F24J50, is that right? The specified part number doesn’t exist, and looks like it’s an incorrectly formed version of this part (same part, with some digits/characters transposed).
- I used the existing Infrared demodulator, TSOP38238 rather than TSOP34838, which is not in at mouser and won’t be for another two or three weeks. Is there a special reason why the latter was specified?
- On the board I have (same as in the picture on the project page), there is no reset switch placed. I don’t know if the switch is obsoleted by software or some such, but if it’s not, it’ll have to be jerry-rigged anyway, so there’s no sense in buying a part that we can’t solder.
- I used the BC81840MTF as T1, rated in the parts listing as 800mA+ when the project calls for 1A+, is that a problem? It seems to me like 1A for an LED is insane, but then that’s what the BOM on the project page calls for. Is there a problem here?
Assuming these points all check out, the project cart should be good to go! HOWEVER! An astute reader will note that the quantities are all higher than required. I like to order extras of EVERYTHING, especially the little parts, since I ALWAYS seem to lose parts to the carpet (last project, it was a $15 MSOP-10 ADC. Thank goodness the project budget paid for one or two extra). This is obviously more critical with the small, cheap parts (0805 resistors and caps) than it is with the big parts (PICs, LEDs). You could probably shave a fair few dollars off the project cost by making these quantities closer to what’s actually required. And in fact, when I order, I probably will. Something to consider.