HP 50G - Any way to increase the IR TX/RX range?

[Katie Wasserman]

I just tried a few tests of the 50g and the 82240B printer. From what I can tell the calculator to printer distance is so very short becasue they are not using the same carrier frequency. The 82240B wants a 38KHz carrier but the 50g is generating a 32KHz carrier (I measured this). This can be remedied by using a 33KHz receiver (a little off still, but much closer) like the TSOP38233 and modulating an IR emitter at a carrier frequency of 38KHz. Pretty easily done, with something as simple as a 555 chip.

I don't have any 33KHz receivers at the moment, but I'll do some more playing around to try to confirm this hypothesis.

[followup]

So, I made a little repeater using a TSOP38238 IR receiver (this one is for 38KHz but has a pretty wide bandwidth) and a 555 timer to get close to a 38KHz modulation frequency and I can get a range of better than 30 cm from the calculator to the IR receiver and a good range from the IR emitter to the printer depending on how much power is used. I'm sure that I'd get a better range form the calculator to the IR receiver using the TSOP38233 (desinged for 33KHz)

However, a 555 timer with RC components is not a good choice for this project as the frequency will drift with voltage and temperature. A crystal or ceramic resonator would be a better choice. Also, you need to be careful to isolate the IR receiver from the IR emitter or it will feedback -- I had this problem at first.

Instead of reinventing the wheel here and given that: (1) almost all modern IR receivers seem to be more sensitive than the one built into the 82440B and (2) the need to isolate the IR receiver form the IR emitter. I suggest that buying almost any commercial wired IR extender will do the trick almost as well as a custom solution.