>>(I'm assuming that you're measuring the frequency with a micro) Jinx: yes, I have done the measurements with my 16F84 datalogger. Output of the circuit (assembled on the breadboard) connected to RA4/TOCKI, (frequency values send through RS232 to a CasioPV as a data terminal display). But tested also with a good digital multimeter: the absolute values aren't identical to those of the logger due to the different algorithm of the routine, but absolutely proportionals. Using tables: sincerely, I wouldn' t use tables at the moment because the EEPROM code space is actually very little (about 100 code lines don't seem sufficients), moreover the final "conductivity-logger" will be on a 12F629. However, tables may be useful if I will use at least a 16F628. >>I have (somewhere) a circuit for a synthesiser VCO that's a very good >>1V / octave based on an LM301A with split supplies, so it can be done. >>Rather than use the probes in the negative feedback path, use them >>as a leg in a resistive divider to generate voltage from a buffer Well, maybe it will necessary a different chip than LM358: I have a little knowledge of Electronics and I didn' t imagine that the frequency values could be so differents from that I imagined! thanks for the suggestions Marco ----- Original Message ----- From: "Jinx" To: Sent: Wednesday, April 16, 2003 12:05 PM Subject: Re: [EE]: OP-AMP squarewave oscillator > > Is it correct that the frequency values aren't linear? > > (I'm assuming that you're measuring the frequency with a micro) > > Does it matter if they aren't ? Rather than try to correct the circuit > to make it linear, use tables. The values in the tables could be set > up for each set of probes, if you find there's a significant variation, > by calibrating with standard solutions and flashing the tables > > There are linear VCOs, op-amp, transistor and digital, around if you > look through op-amp AN notes at somewhere like NatSemi's site, or > simply Google for "Linear VCO" > > I have (somewhere) a circuit for a synthesiser VCO that's a very good > 1V / octave based on an LM301A with split supplies, so it can be done. > Rather than use the probes in the negative feedback path, use them > as a leg in a resistive divider to generate voltage from a buffer > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu