Easy-simple IR Detector2

Figure 1: SOIC soldering is not bad with a needle nose gripped very tightly in a C clamp.

Unfortunately, the SD003-151-001 chip (the photodiode) came in a surface mount package.  Perhaps it is available in other forms, but I didn’t find them.  So, I use the same technique for surface mount parts as for SOIC breakout boards, but put the diodes on little (1 inch square) proto boards.  It’s nice required to have a light magnifier and an eye shield (to avoid the halon in the solder, and to avoid the splatter so as to prevent it from hitting the eyes)  – to do this.  I have a lockable needle nose that keeps pressure on the chip to hold it in place.  This is not advice (soldering is inherently something that must be done carefully) – so folks unsure about this almost everybody should have a solder-savvy friend do the metal melting.  It took me about fifteen minutes to wire the whole gadget, so a drink of the friend’s selection (after the soldering of course) – may do the trick.

Figure 2: More of the same, safety googles and shield required!

Getting back to the IR (or lack thereof) coming from LED lamps, I wonder if our brain’s rat-sense navigation is badly effected if we don’t get IR exercise in our eyes.  Of course, a trip to the out-of-doors will provide it, but what about nursing home patients who never see the light of day?

Too much IR is a bad thing, and is why high shade welder’s goggles filter it out, as well as the UV (usually).  I use low shade welder’s goggles in place of sunglasses, but I don’t recommend this habit to others.  I have various theories for doing this, but the elimination of IR and UV to such a strong degree may not be healthy. I sometimes stumble over the feet that I can’t see very well.  Also – I could be killed at a traffic light because I can’t see the red.

On the other hand, the welder’s goggles give an IR perspective to any subject that I may want to use in IR photography.   For some reason (I don’t know why) – the “look” as seen through the welder’s goggles is very similar to the “look” of IR photographs.  Maybe a physicists could answer this one.

I used my little gadget to test my welder’s goggles.  Well – they aren’t the typical welder’s goggles.  They are made to be sporty, and look much like wrap-around dark (very dark) sunglasses.  I don’t recommend using such a gadget as I have built to test real welder’s goggles, used for welding, because there is no real calibration on my device, and it may not be foolproof in terms of reliability.

Anyway, my shade 3.0 glasses reduce IR from a 3.5 volt reading (using 60 watt incandescent reference) – to a .3 reading.  My shade 5.0 goggles reduce the 3.5 reading down to .08.   This is however, entirely uncalibrated, and depends on my particular vernier control position, and is not reliable for real tests (important!).

The “second edition” of my device will use an op amp.  I would like to use a single ended supply for this, utilizing a 9V battery.  Most split supply solutions add complication, and noise (cap pump based).  I want the upgraded version of the detector to “see” low levels, noise free.  I figure I should be able to improve the sensitivity by several hundred times with an appropriate circuit.

To get around the split supply requirement, I think it will be necessary to use a rail-to-rail op amp, to get past the saturation.  My initial op amp selection was the OPA847 (a fine device I no longer have, thanks to backwards schematic reading versus my breadboard).  Six bucks each too – ouch.

So, I’m thinking about the Analog Devices LT1001.  I’m thinking guessing that it’ll work on a single ended supply (just a nine volt battery).  Stay tuned for the first smoke test (at least they’re only $3 each).

I bought the 1.3 um (micro-meter) LED from Digikey (part number 1125-1425-ND, which is MFG # MTE0013-525-IR) – as an IR source for playing with edition I of my gadget.  The 1300 nm LED is about $15 IIRC, but I wanted to see if the responsitivity of the receiving diode could be tracked.  So, I have other IR LED frequencies as well (including cheapo dime-for-a-dozen TV remote varieties at 980 nm).

Oddly, the falloff from the center wavelength (1.3 um = 1300 nm) was not nearly as much as described on the mfg data sheet for the receiver diode. In other words, the responsivity chart the manufacturer provides is a normal curve, but my empirical result produced more of a highly rounded square wave sort of curve.  I’d guess that is might be due to the circuit I used.  My original intent was to make a sort of spectrum analyzer based on the criteria.

To be continued …

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