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Topic: USB IR Toy v1.1 Rev 1 parts (Read 1171 times) previous topic - next topic

USB IR Toy v1.1 Rev 1 parts

Okay, I'm working on getting together the parts for doing my Free PCB build for the USB IR Toy v1.1. My best guess based on tracing and pad placement/orientation is that this is a Rev 1 board. I'm fairly certain that I've got all the components, but I'm down to the LED for TX and R4 parts. For the LED I chose this. Based on availability of the 0805 resistor values at mouser, I assume that I would need to put 4 10Ohm, 1/4W resistors in parallel or 4 ~156Ohm, 1/4W resistors in a series? Am I missing something here, or is this one just that tricky? Any tips on how to properly carry this out? The only picture of this particular revision I can find only shows a single resistor on the PCB...

Re: USB IR Toy v1.1 Rev 1 parts

Reply #1
rev 1 added only the new IR detector sensor. Everything else can be exactly as in v1. For best transmit range you will need a smaller than specified resistor because of the inferior transmitter on v1. Since you only do short pulses a little at a time, the resistor does not need to be rated the full value of the LED current, only be ok on average. Still, if the IR Toy is ever stuck 'on' it could cause damage, and that is why we shipped it with a bigger value resistor.
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Re: USB IR Toy v1.1 Rev 1 parts

Reply #2
I assume that by smaller than specified, you mean smaller resistance compared to the 180Ohm one the v1 partlist? I know that the "ideal" resistor for my selected LED is a 39 Ohm, 1W. Considering the 0805 resistors in that amount of resistance max at 1/4W, should I just use a single one of those? I'm still pretty new to actual circuit design and calculations, so I'm not sure which value is okay to fudge a little; I just know that 5V is coming from that USB and that the LED need about 1.6V to run properly and not burn out or anything.

 

Re: USB IR Toy v1.1 Rev 1 parts

Reply #3
Quote
39 Ohm, 1W. Considering the 0805 resistors in that amount of resistance max at 1/4W, should I just use a single one of those?

Yes, that is safe, assuming there is no hardware failure that stops with the LED 100% on. Even then, probably not terrifically dangerous.

1W is needed for continuous use. In normal use, it is on 50% in tiny bursts. That averages out to way less than 1/4 watt.
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