cs_ACR01B2C.h File Reference

#include <cfg/cs_Boards.h>
#include <cfg/cs_DeviceTypes.h>

Include dependency graph for cs_ACR01B2C.h:

Go to the source code of this file.

Functions
void	asACR01B2C (boards_config_t *config)
	The very first plug that is delivered to Crownstone users. More...

Function Documentation

asACR01B2C()

void asACR01B2C

(

boards_config_t *

config

)

The very first plug that is delivered to Crownstone users.

Voltage measurements.

• The ACR01B2C has a voltage divider R12/R13 of 82k/18k. This means the opamp will receive input around a voltage level of 3.3V * 18/(18+82) = 0.594V.
• This is a non-differential measurement. It uses an internal reference voltage of 0.6V.
• The ADC is configured for a range of 0 ... 1.2V. A gain of 1/2 with respect to the 0.6V.
  • The other software option would be a reference of VDD/4 (more robust against deviations in true VDD voltage).
• The ADC is configured to use 12-bits, 4096 levels.
• Zero is at 0.594 so 6 mV below 0.6V. If we divide 1.2V over 4096-1 we have 0.2930 mV per interval.
• Hence 6 mV corresponds with 20 levels below 2047 (4096/2-1), which is 2027 (voltageZero should be set to this).
• The resistors R12/R13 when considered parallel have an equivalent resistance of 1/(1/82k+1/18k)=14.76k
• The capacitor at the voltage measurement input is 10 nF and its reactance is 1/(2pi*f*C).
• With 50 Hz this is 1/(2pi*50*10*10-9) = 318 kOhm and with 60 Hz this is 265 kOhm.
• Total voltage divider to calculate gain of opamp is then 10.3M versus 14.76k.
• The opamp gain becomes 14.76k/10.3M = 0.001433 (or 697.83x when inverted).
• The multiplication factor to go from ADC values to V_in is 0.0002930 * 697.83 = 0.20446f.

TODO: Here voltageZero=2003 is used instead of 2027. Check. TODO: Here voltageMultiplier=0.2f is used instead of 0.20446f. Check. TODO: The values used now might be empirical. Replace by theoretic values or tell why the calcluation is incorrect.