08M ADC Functionality

[TomMystery]

Quick Question: Is there any way to change the reference min/max voltage on any of the picaxes, speifically the 08M, or are they set at 0 to VDD (5V)?

 

[premelec]

The short answer is no... that said if you changed the PICAXE Vdd lower than 5 volts it then has a lower reference voltage. For higher ADC input voltages use a resistive divider with less than 10K resistance.

Otherwise use an OP Amp to jack up lower voltages.

Note that if you use two ADCs in an 08M with version 9 firmware you need to do two READADCs in sequence and use only the second read - this was corrected in later firmware.

Happy AXING!

 

[TomMystery]

In that case what is a good external 1 channel ADC that uses an external reference voltage? The Max1242 looks like a good solution, any other ideas?

 

[premelec]

It might depend more on what you can easily obtain, price, power requirements and how you want to communicate with the chip... there are so many chips around these days...

If the unit you mention meets your requirements why not use it?

To review some of the selection www.ti.com is good and www.analog.com as well as maxim-ic etc... sometimes it doesn't pay off in time to look too thoroughly if you have something at hand which does the job and you aren't manufacturing thousands of units...

Have fun...

 

[Michael 2727]

What voltage do you want to measure ?
A simple 2 resistor voltage divider,
and an over voltage clamping diode should
be enough for many applications.