From abruno@zeta.org.au Fri Feb 2 07:30 GMT 1996 Return-path: Received: from godzilla.zeta.org.au by soulcage.inmind.com (8.6.10/SMI-4.1) id HAA11055; Fri, 2 Feb 1996 07:29:51 GMT Received: (from abruno@localhost) by godzilla.zeta.org.au (8.6.9/8.6.9) id SAA02145 for thogard@soulcage.inmind.com; Fri, 2 Feb 1996 18:27:46 +1100 From: Andrew Bruno Message-ID: <199602020727.SAA02145@godzilla.zeta.org.au> Subject: The interface cct. To: thogard@soulcage.inmind.com (Tim Hogard) Date: Fri, 2 Feb 1996 18:27:46 +1100 (EST) In-Reply-To: <199602012110.VAA03158@soulcage.inmind.com> from "Tim Hogard" at Feb 1, 96 04:10:57 pm X-Mailer: ELM [version 2.4 PL23] Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-Length: 5673 Status: RO Here is the artical..... cut it out and stick it on your page. Good luck (?) Hope you like it. Greetings fellow GPS users. I have recently bought one and ofcourse the computer interface was a little bit too expensive for my likes. I appreciate that there is a circuit to build listed here (maybe still?) that requires op amps, diodes and resistors. I sat down with a c.r.o. and looked at the output of the GPS and noticed that it was TTL level (0 - +5v) soooooo................ Here is my circuit. Things needed: 1 x Max232 chip 2 x 10u 6.3v Electros 2 x 10u 16v Electros (and a 5volt supply.) The supply can be either an external 5 volt one, or if you are using an external supply to power the GPS at the same time, put in a 7805 (with its two caps). Ok, so here it is! +5v | | +--------------------+-----------+ + | | | === 100m 10v | === 10u | | | + 6.3v E | 16 | +-----###########------+ + | 1 # # 2 10u === # # 6.3v | # # +-----# # 2 # # # MAX232 # +-----# # + | 4 # # 10u === # # 16v | # # +-----# #------+ 5 # # 6 | # # === 10u # # | + 16v # # E # # DB25 DB9 * data out -------# -|>- #---------- 3 2 Rx on computer 11 # # 14 To inverter # # To the computer (RS232) data in -------# -<|- #---------- 2 3 Tx on computer 12 # # 13 ########### E = ground. I won't promise you this will work, but looking at the voltages comming out of the GPS and the like, it SHOULD. USE AT OWN RISK! (Sorry, I guess it is in my best interests to say that.) The chip is not that expensive and 4 cap's.... I suggest that it is housed in a little box (jiffy box, as called in Oz) at the end of the cable comming out of the GPS, that way the external supply can power both the GPS and this unit. Ofcourse you will have to put in the 7805 and a copule of caps, too. You then buy a DB9 (or DB25 if you don't like the number 9) and put it on the box. * A suggestion here is to "reverse" the pins. IE: where pin 2 on a DB9 should be RD, and pin 3 is TD, connect the chip's pin 14 to pin 2 of the DB9 and pin 13 to pin 3 of the DB9. This way you don't need a null-modem cable. Here is the inverter cct that is needed between the MAX chip and the GPS.... (I used a 4049 chip, and that is for what this cct is drawn...... ) ######## data out 3 # # 2 data out -------# #--------- To GPS cct # 4049 # To MAX232 chip -------# #--------- data in 4 # # 5 data in # # # # 8 # # 1 +--# #--- +5 v | ######## E Now for the power problems..... The 100mfd Electro shown at the top.... That is for supply smoothing, otherwise it doesn't like it too much and I suggest that it is there.... Problems: (to call it that) The MAX runs of +5 volts, but the GPS is more suited for +5 to +20 (nom). To help with the connections and keep the problems to a minimum, a suggestion is to put a 7805 on the board and use it to supply both chips. It is powered from the EXTERNAL supply connected to the GPS; which is most likely when you are wanting to the GPS with a computer anyway. You COULD use the DTR line form the computer, but I don't advise that. Here is a quick "overlay" of what I did - using vero board. +----------------------+ # |# | # 7805 |# C | # |# +-------+ | | C | | | | | | | C 100mfd electros | | MAX232| | | | | O | O Tant caps | | | O | | | | O | | +---^---+ O | | 1 | | | | 1+---u---+ | | | | | | | | | | | 4049 | | | | | | | | | | | | | | | +-------+ | | | | | +----------------------+ Notice that I have put 2 100mfd electros.... One is on the input of the 7805, and one on the output. This cct DOES work, but I haven't YET tested the computer to GPS side of it. Hope that it works..... Thanks to all who helped me with the "debugging"! Andrew Bruno abruno@zeta.org.au PGP key with finger.