leftyretro
New Member
Hi Group;
Just acquired a picaxe stack 28X kit this week and got it assembled and going yesterday. I'm very impressed with the whole picaxe system and know I'm going to have a blast.
I've been exploring the features and learning the software. One quick experiment I did was to test out the ADC and PWM features. I wired a 20 turn trimmer pot from 5 volt vcc to ground and routed the wiper to the ADC channel 1 input. I wired a 5k ohm resistor from the PWM output and integrated it with a 2.2 mfd cap to ground. I then put the picaxe in a loop as follows:
main: rem loop back ADC to PWM
Readadc10 0,W0
pwmout 1,249,w0
goto main
This works fine but the measured results with a benchtop Fluke 45 DVM appears to have more resolution then I would expect.
My think is a 10 bit A to D with a 0-5v range should result in around 5 millivolt steps (5/1024) as I adjust my pot, however my readings after intergrating the PWM is more like 100 micro volts steps. It's touchy to try 100 uv steps but clearly I can set 1 millivolt steps with no problems.
So where is my thinking off. Why do I appear to have greater control of output voltage resolution then 10 bits ADC conversion would account for.
Thanks
Just acquired a picaxe stack 28X kit this week and got it assembled and going yesterday. I'm very impressed with the whole picaxe system and know I'm going to have a blast.
I've been exploring the features and learning the software. One quick experiment I did was to test out the ADC and PWM features. I wired a 20 turn trimmer pot from 5 volt vcc to ground and routed the wiper to the ADC channel 1 input. I wired a 5k ohm resistor from the PWM output and integrated it with a 2.2 mfd cap to ground. I then put the picaxe in a loop as follows:
main: rem loop back ADC to PWM
Readadc10 0,W0
pwmout 1,249,w0
goto main
This works fine but the measured results with a benchtop Fluke 45 DVM appears to have more resolution then I would expect.
My think is a 10 bit A to D with a 0-5v range should result in around 5 millivolt steps (5/1024) as I adjust my pot, however my readings after intergrating the PWM is more like 100 micro volts steps. It's touchy to try 100 uv steps but clearly I can set 1 millivolt steps with no problems.
So where is my thinking off. Why do I appear to have greater control of output voltage resolution then 10 bits ADC conversion would account for.
Thanks