From tw45639@vub.ac.be Wed 28 Jun 95 13:43:54 Newsgroups: comp.sys.hp48 From: Dave Arnett Subject: Re: long distance IR Message-ID: Date: Mon, 26 Jun 1995 17:31:17 GMT References: <19JUN95.25663706.0062@VM1.MCGILL.CA> <3sdf2m$nov@newsbf02.news.aol.com> <3si0pp$nca@hustle.rahul.net> Matthew Carlson wrote: >WayneAtDSN (wayneatdsn@aol.com) wrote: >: About withdrawing a resistor: I've opened up the case, and as far as I can >: see, the two IR leds feed directly into one of three IC's. To me: There is >: no IR cripple. >Trust me there is a shunt resistor to limit the current in the reciever. >Where it is or how it is implamented is another thing. They could have >used an op-amp in one of the ic's for it. Or they could have just used a >real resistor in the ic. It could be a transistor circuit. Anything that >limits the current. If you give me the part numbers of those ic's, a >diagram of how they are connected to the reciever and any resistors or >caps they connect to. I may be able to help. Never say we keep technical info from the intelligent public.... Vco-------------- | | | | R R R 1M R 18k R R | | | C | Q |---------BQ |------------Pin 160 | Q PNP IR Sens | "IRI" | E C Yorke CPU chip | | Q 00048-80048 | |------RRR---------------BQ (Different part | | 220k | Q on S-series, | R R E NPN same function.) | R 220k R 560k | | R R | C | | | Q | | | QB---------| | | Q | | | E NPN C | | | === 0.022 uF | | | C | | | | | | | | | | GND-----------------------------------------| For Info, Vco is the 5V power supply which is NOT energized during the sleep modes. And Yes, the IR is sensed through a photosensitive PNP transistor. I hope this diagram has no typographical errors. Use it at your own risk and discretion. THis describes the G and S series HP48 calculators, as designed and shipped from the factory. Dave. ------ I don't speak for HP when I post here, and I do not recommend opening HP48 calculators. I also maintain that "crippled" is an incorrect word for describing the HP48 IR detector circuit.