Ok, I'll check with voltmeter before connecting it to the IOIO just to be 
sure..

Thank you very much for the quick reply in your busy day.. :)

On Wednesday, August 9, 2017 at 1:08:21 PM UTC+7, Ytai wrote:
>
> I don't think the probe actually emits negative voltage. I think the table 
> is an example with voltages relative to some offset that the next section 
> describes how to measure. Essentially, you're doing a 2-parameter 
> calibration.
> If you're unsure, connect a voltmeter to the sensor before connecting it 
> to the IOIO.
>
> On Aug 8, 2017 9:11 PM, "Maximillian" <felix.c...@gmail.com <javascript:>> 
> wrote:
>
> Hi All,
>
> I need to read pH using this product
>
> https://www.dfrobot.com/wiki/index.php/PH_meter(SKU:_SEN0161).
>
> I found this table on the description:
> [image: Ph-mv.jpg]
>
> The table said that it will give negative voltage (0.00 mV to -414.12 mV) 
> for pH value 7-14..
>
> I've been searching through this group, I think I found that I should not 
> feed IOIO analog input pin with negative value (only 0v - 3.3v CMIIW).
>
> I'm not really experienced with electicity, so any suggestion is really a 
> big help.
>
> Is there any solution for the negative value?
>
> Maybe using another componen to convert flip it to positive,
>
> or offset the voltage to be positive since it only have around 828mV range 
> (-414.42 mv to +414.42 mV). So maybe I can just set the 7pH from 0V to 
> maybe 2V, then the lowest voltage will only be 2V - 414.42mV, and the 
> highest voltage will only be 2V + 414.42mV
>
> or any better/proper solution?
>
> Thank you.
>
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