---- START NEW MESSAGE --- Received: from cherry.ease.lsoft.com [209.119.0.109] by dpmail10.doteasy.com with ESMTP (SMTPD32-8.05) id AFC7A580068; Fri, 30 Jan 2004 13:42:31 -0800 Received: from PEAR.EASE.LSOFT.COM (209.119.0.19) by cherry.ease.lsoft.com (LSMTP for Digital Unix v1.1b) with SMTP id <5.00CC53E4@cherry.ease.lsoft.com>; Fri, 30 Jan 2004 15:42:14 -0500 Received: from MITVMA.MIT.EDU by MITVMA.MIT.EDU (LISTSERV-TCP/IP release 1.8e) with spool id 5318 for PICLIST@MITVMA.MIT.EDU; Fri, 30 Jan 2004 15:42:07 -0500 Received: from MITVMA (NJE origin SMTP@MITVMA) by MITVMA.MIT.EDU (LMail V1.2d/1.8d) with BSMTP id 9459; Fri, 30 Jan 2004 15:41:03 -0500 Received: from bay8-dav9.bay8.hotmail.com [64.4.26.113] by mitvma.mit.edu (IBM VM SMTP Level 430) via TCP with ESMTP ; Fri, 30 Jan 2004 15:41:02 EST X-Warning: mitvma.mit.edu: Host bay8-dav9.bay8.hotmail.com claimed to be hotmail.com Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Fri, 30 Jan 2004 12:41:04 -0800 Received: from 67.65.155.200 by bay8-dav9.bay8.hotmail.com with DAV; Fri, 30 Jan 2004 20:41:04 +0000 X-Originating-IP: [67.65.155.200] X-Originating-Email: [jsears2027@hotmail.com] X-Sender: jsears2027@hotmail.com References: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1158 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 X-OriginalArrivalTime: 30 Jan 2004 20:41:04.0819 (UTC) FILETIME=[616A6830:01C3E771] Message-ID: Date: Fri, 30 Jan 2004 14:41:01 -0600 Reply-To: pic microcontroller discussion list Sender: pic microcontroller discussion list From: James Nick Sears Subject: Re: [PIC:] 16LF877A A/D To: PICLIST@MITVMA.MIT.EDU Precedence: list X-RCPT-TO: Status: U X-UIDL: 371856568 Thanks for the idea. I looked in the Midrange Ref Manual and the minimum for Vref (Vref+ - Vref-) is listed as 0V (no latchup) and 3V (10 bit resolution). Wish I would have seen that awhile ago. At any rate, does anyone have experience using the A/D with a ~1.25V reference? The one that works works beautifully, while the others are consistently wrong and read around the same (wrong) voltage so hopefully it is some other problem although I guess it's possible that I got ahold of a super 877A that happens to work well for low Vref. Ahh boy.... Nick ----- Original Message ----- From: "I Forse" To: Sent: Friday, January 30, 2004 1:53 PM Subject: Re: [PICLIST] [PIC:] 16LF877A A/D > Nick > > Not sure about the 877A but the 877 requires a Vref of 2.5V to work > properly, which may explain why one unit works and the others do not. > > Regards > > Ian > > > -----Original Message----- > > From: pic microcontroller discussion list > > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of James Nick Sears > > Sent: 30 January 2004 19:37 > > To: PICLIST@MITVMA.MIT.EDU > > Subject: [PIC:] 16LF877A A/D > > > > > > Hello, > > > > I am trying to finish my datalogger project and I am having > > problems with A/D converters returning wrong values. I have one > > board programmed and working fine, while the next 4 that I have > > done all have the same problem so I am thinking I accidentally > > broke the software but I can't say 100% for sure. I am working > > now trying to get the working board programmed with the current > > program to see for sure but I have to do a little bit of wiring > > to connect a different supply to the board to get a high enough > > Vdd to program. The temperature sensor that I am connecting > > reads 23 degrees F on the bad boards rather than my 65-70F room > > temp on the good one (0.3922V instead of ~0.55 - 0.6V). > > > > I then programmed it to overwrite the temporary A/D values saved > > in user registers (which are later saved to EEPROM after the ISR > > completes) with 00000010 00000000, which is half of full scale > > and everything worked as expected (showed 0.625V in my PC > > software, which is half of my 1.25V reference) so I know that the > > EEPROM, Serial Comms, etc are not to blame. > > > > I have also measured the voltages at the PIC pins AN0,VRef+,and > > VRef- and they all look fine (around 0.6V,1.25V, and 0V, respectively). > > > > And finally I checked my A/D configuration (ADCON0 and ADCON1) > > and everything looks fine. > > Conversion Clock: Fosc/32 (also have tried Fosc/64 - I am running > > a 4MHz Xtal by the way) > > Channel 0 is selected > > Port is configured for all analog inputs with Vref+ and Vref- on > > AN3 and AN2 > > > > My power supply looks pretty good. I get a 5-10mV dip when a > > pair of LEDs blink to show the the serial port is active and when > > that port is active the supply dips about 40mV in little pulses > > at about 15kHz which I gather are caused by the charge pump in > > the RS232 driver. In any case, with the serial cable unplugged I > > am looking at <=15mV p-p noise on the supply and the A/D still > > doesn't work right. > > > > Who's got the right idea??? > > > > Thanks, > > Nick > > > > > > PS: Code is attached > > > > > > > > > > > > > > -- > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > > > > > > > -- > > Incoming mail is certified Virus Free. > > Checked by AVG Anti-Virus (http://www.grisoft.com). > > Version: 7.0.211 / Virus Database: 261.8.1 - Release Date: 30/01/04 > > > -- > Outgoing mail is certified Virus Free. > Checked by AVG Anti-Virus (http://www.grisoft.com). > Version: 7.0.211 / Virus Database: 261.8.1 - Release Date: 30/01/04 > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body .