FJMSoft Posted June 21, 2007 Report Share Posted June 21, 2007 Hi, Im trying to build an 8051 based midibox, but, I have some trouble with CD4051, how much time I need to wait between each input change? Thanks. Quote Link to comment Share on other sites More sharing options...
seppoman Posted June 21, 2007 Report Share Posted June 21, 2007 This info is stated in the datasheet of your actual CD4051 variant. But normally the acquisition time of the ADC will be much higher than this. You can just get one AD value, switch to the next channel and wait perhaps a few NOPs.Seppoman Quote Link to comment Share on other sites More sharing options...
FJMSoft Posted June 21, 2007 Author Report Share Posted June 21, 2007 Hi Seppoman, thanks for your answer... I'm waiting like 1,2 mili second, and same problem... One potentiometer slightly changes the value of another... My CD4051 common output is connected to input of ADC0804, can you see for me, how much time ADC0804 needs between each voltage input change? Thanks. Quote Link to comment Share on other sites More sharing options...
TK. Posted June 21, 2007 Report Share Posted June 21, 2007 What is the resitance of your pots? Maybe it's too high - this can cause such a crosstalk issue.Best Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
FJMSoft Posted June 21, 2007 Author Report Share Posted June 21, 2007 Hi Thorsten, thanks for your answer, I'm using normal 10k linear pots. Quote Link to comment Share on other sites More sharing options...
TK. Posted June 21, 2007 Report Share Posted June 21, 2007 This should be ok... what is the range in between the conversion results are jittering?If it is +/- 1 LSB, this would be normal (the 4051 adds some noise..) - this has to be compensated via software (just use a "deadband" algorithm)Best Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
FJMSoft Posted June 21, 2007 Author Report Share Posted June 21, 2007 The jittering isnt the real problem, the problem is the crosstalk, I need to make microcontroller wait very very long to lower crosstalk (like 25000 micro second) Quote Link to comment Share on other sites More sharing options...
TK. Posted June 22, 2007 Report Share Posted June 22, 2007 The resulting effect when the setup time is not long enough is jitter, no?However, regardless of the definition, my question was: how high is the unexpected offset?I know many people who implemented their own MIDI controller firmware in the past, and most of them were not aware of methods how to make pot changes stable within the target resolution. Yes, the fun begins with multiplexing, where voltages are not settled, and the dynamic switching causes spikes on the analog inputs.At the beginning of the MIDIbox project I needed more than one year to work out a method - later I discovered that it is very commonly used by experts. ;)Best Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
FJMSoft Posted June 22, 2007 Author Report Share Posted June 22, 2007 Hi Thorsten, thanks for all attention you are giving to me.I'm getting crosstalk, the jitter is normal, +-1bit.You think 25000 micro second + adc latency is ok for each pot read?How do you do with midibox? Can you teach me?I'm using 8051 as microcontroller, ADC0804 as converter and 4051 to multiplex.Do you program 8051?Thanks. Quote Link to comment Share on other sites More sharing options...
TK. Posted June 22, 2007 Report Share Posted June 22, 2007 25mS is far to much, in MIOS I'm using a setup time of 100 uS before starting the conversion. The jitter is ca. +/- 1 LSB as well. It is compensated with the deadband algorithm which is described somewhere in the forum (use the search function - you have the keyword now), and at http://www.wikipedia.com of course.8051: I played with a 80c535 ca. 15 years ago... so far I remember it has an integrated ADC. I wouldn't use such micros today anymore - there are cheaper, higher integrated parts for less money.Best Regards, Thorsten. Quote Link to comment Share on other sites More sharing options...
FJMSoft Posted June 22, 2007 Author Report Share Posted June 22, 2007 I think 25ms is far to much too. I think I have some problem here, but cant figure out, i think i need help. (I hate adc0804) Quote Link to comment Share on other sites More sharing options...
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