analog adc reading resolutions of any picaxe

[peter howarth]

I have a project that needs to accurately read down to as low as 50mV in 50mV increments up to about 2 volts, for about 30 increments of 50mV.. How accurate can I go with the picaxe devices of 08m, 14m, 20m 28x2 and 40x2 and preferably not use an external resonator..

 

[AllyCat]

Hi,

Absolute Accuracy is a complex topic, but 50 mV in 2.0 volts is 2.5% so it should be fairly easy to calibrate/validate a test measurement using any reasonable multimeter or dedicated Voltmeter. It's mainly a matter for your Hardware design, i.e. Resistor tolerances/ratios/stability and the Reference Voltage (e.g. External Supply Regulator or internal FVR), etc..

However, any of those PICaxe chips should be able to achieve better than 5 mV resolution (i.e. ten times higher than your requirement) using the READADC10 command (and of course a Word variable).

Cheers, Alan.

 

[hippy]

READADC10, even with a 5V supply, will read to a resolution of around 5mV so any PICAXE should be fine.

 

[Goeytex]

If 2.0V is the max input voltage then you can use the 2.048V internal reference (FVR). With READADC10 the resolution will be 2 mV. With READADC it .will be 8 mV. With careful attention to grounding and component values you should be able to get an accuracy of +- 2 LSB.

To return an output in 50mv increments where 0 to 2V = 0 to 40 is a matter of simple math.