HP48SX InfraRed power.


I would like to know if there is any way to increase the power of the HP48SX IR transmiter?

I will appreciate very much if you could tell me what components I should change in the calculator.

Best regards, Tal. email: td@chem.ch.huji.ac.il


This link will help you:


There is also a text file here on the hpmuseum site: (the same text)


As you see in the schematics on page 6, the driver for the IR LED ia a simple switch. You might succeed by changing R1, or possibly R2, but you should watch the IR LEDs datasheet before trying.

It is well known in communications engineering, that rising transmission power has a low effect on transmission distance.

There is also the risk of killing the diode or overloading the OUT pin, which is (i guess) a CPU pin.

If you want to increase distance, you should raise the "antenna gain" (higher LED efficiency; narrower, more "concentrated" beam, ...)

Also, please consult the datasheet of the diodes mentioned in the technical interfacing guide.

The receive circuit is rather difficult to improve, because there are no filters. As I mentiones in an earlier post, a time-variant filter should do a rather good job, maybe together with a Markoff chain. Increasing the gain is not the right way to solve the problem (though it is a part of it).

The main problem in this transmission method is, that it isn't modulated, so that there can be no sharp passband filters in a receiver circuit. I heard, the Ericsson 888 mobile phone uses a similar (horrible) format transmitting short pulses for a RS-232 transmission. This saves battery, but it is a unpleasant way of transmitting data over more than 5 cm.

Are you an engineer, or does anybody else want me to explain some words used in this message? Feel free to ask here in the forum or via email.

Sorry, Tal, I haven't found my old schematics til now. Be assured, as soon as I find them, you will be the first who receives a copy.

Possibly Related Threads...
Thread Author Replies Views Last Post
  HP41 emulator for HP48sx - keyboard overlay needed Doug (NYC) 3 810 12-31-2012, 03:11 PM
Last Post: Allen
  HP48SX seems fully functional won't run SELF TESTS? Bruce Larrabee 5 995 07-16-2012, 11:04 PM
Last Post: Luiz C. Vieira (Brazil)
  HP-42S / HP-48 infrared connection Kees Bouw 6 1,033 07-09-2012, 11:33 AM
Last Post: Christoph Giesselink
  WP 34S - Successful installation of infrared port Gerson W. Barbosa 7 1,125 06-01-2012, 06:05 PM
Last Post: Gerson W. Barbosa
  Did We Miss The 20th Anniv. of the HP48SX? Jake Schwartz 6 830 03-19-2010, 05:55 AM
Last Post: Bill Zimmerly
  HP48SX accuracy questioned. Pal G. 3 673 09-10-2009, 09:01 PM
Last Post: hugh steers
  HP48SX LCD problem... Geoff Quickfall 4 688 08-16-2009, 04:35 PM
Last Post: NACHO
  Kermit K95 ver 2.1.3 GUI and the hp48sx Mike Reed 6 879 01-28-2008, 11:37 PM
Last Post: Mike Reed
  Infrared enabled calcs to iMac Intel ? Olivier TREGER 4 686 03-26-2007, 01:17 AM
Last Post: Olivier TREGER
  PC power > HP-calc power, yet... $PC = $HP48gx ECL 7 961 12-03-2006, 08:04 PM
Last Post: Tim Wessman

Forum Jump: