[AirCare] InTheAir - Week 11: CC3200, Energia and analogRead()

RE: [AirCare] InTheAir - Week 11: CC3200, Energia and analogRead()

shabaz — Sat, 10 Jan 2015 20:14:44 GMT

Hi guys,

I've not used Energia with the CC3200 so I've not checked the ADC code, but I had a look at the CC3200 datasheet and the ADC pins are for signals from 0 to 1.4V, but also expects the source impedance to be 100 ohms or less. This means that for most use-cases an opamp is essential. The dust sensor expects a load of 4.7k, but dividing it with a voltage divider increases the source impedance, so that will have a discrepancy with readings compared with the Arduino's ADC (which has a much higher input impedance, but is only 10-bit). I don't know if you have an opamp lying around, but if you do, it would be worth adding it.

RE: [AirCare] InTheAir - Week 11: CC3200, Energia and analogRead()

janisalnis — Sat, 10 Jan 2015 18:45:42 GMT

On CC3200 only 3 analog inputs out of 4 work. I would call it a bug.

Free floating analog inputs have some internal offset of +0.6V. It can be measured by a multimeter. This is not like on Arduino. I would call it a bug. So your resistor divider needs to be calibrated with some known input voltages like 5V and 3.3V and 0V.

When you switch from one input to another give a delay so that signal can settle down. Try to read several values in a row and see how many first values to discard.

RE: [AirCare] InTheAir - Week 11: CC3200, Energia and analogRead()

BigG — Sat, 10 Jan 2015 12:09:27 GMT

Very insightful feedback indeed.

Just thought that maybe this ready made module may help The JeeLabs Shop - Analog Plug

Its a MCP3424 analog-to-digital converter with I2C bus interface.