budman1758 wrote: ↑12 Jun 2017, 04:59
Questions. Apparently the ADS cannot measure more than .3 volts above the voltage used to power it. So in order to measure the possible 5 volt output of the anemometer I suppose I need to power it with 5 volt. Do I now need level shifters on the I2c connection?
What determines the I2c voltage? The controller (in this case the ESP) or the ADS module? Is it just whichever voltage is higher? Would a voltage divider on the analog input be a better solution?
The voltage on I²C depends on two simple factors. I²C should have some pullup resistors at one end of the line.
These pull the lines to 3,3V or 5V, depending to which voltage the resistors are connected.
Even the connected I2C circuits may bring their own resistors and voltage - in case of doubt use a digital voltmeter to check before connecting to the ESP.
Alternatively you can use a voltage divider to reduce the voltage.
A divider of 4,7KOhm and 2,2 KOhm will give an output voltage of 1,6V at "full speed" instead of 5V.
So you can cover full range without level shifter.
Also having difficulty understanding the gain setting.
Gain can be set to different values. The given value, for example 6.144V, is the maximum you can measure in that configuration.
So if you connect your wind sensor directly (5V output max), 6.144V is the correct one.
If you use a voltage divider as described above, set it to 2,048V
Remember:
An AD-converter does not give back a voltage reading. It gives back "ticks".
At this setting the ADS works from -6.144V to +6.144V, it has a resolution of 16bit for that. So the positive voltage spans "ticks" from 0 (0V) to 32767 (6.144V).
5 Volts will read of 26667. (26667 ticks * 187,5µV/tick).
With the second setting (Voltage divider and gain setting to 2.048v), full speed will read 25600 ticks.
Then there is the question of the formula needed to convert the voltage to an output that makes sense. I would like it to be in miles per hour. Sorry but most metric measurements don't "hit" me the same way as imperial. Its what I grew up with.
A bit difficult to answer as the ebay page isn't really clear.
"Wind Speed: Output voltage /5*32.4"
I'm not sure, i assume this means (Vout/5) * 32.4. Or is it Vout / (5*32,4) ??
It's not too difficult to change this if i guessed wrong
The ebay offer does not say if this is meters or miles per second.
As we have ticks, not volts you will have to calculate that into the formula to get to a real value.
Then we get a formula:
(ticks from ADS * 0,0001875 *32.4) / 5
If that returns results in metrical you may change it to
(ticks from ADS * 0,0001875 * 32.4 * 0,621371) / 5
for imperial.
For the secondary setting with voltage divider you have to change the formulas to:
(ticks from ADS * 0,0000625 *32.4) / 1,6 (metrical)
(ticks from ADS * 0,0000625 *32.4 * 0,621371) / 1,6 (imperial)
