docs: Update details on using ADCAll object for vref/vbat channels.
This commit is contained in:
parent
70f32f0f73
commit
85d3b6165a
|
@ -18,6 +18,7 @@ class ADC -- analog to digital conversion
|
|||
val = adc.read_core_vbat() # read MCU VBAT
|
||||
val = adc.read_core_vref() # read MCU VREF
|
||||
|
||||
|
||||
Constructors
|
||||
------------
|
||||
|
||||
|
@ -77,6 +78,65 @@ Methods
|
|||
The ADCAll Object
|
||||
-----------------
|
||||
|
||||
Instantiating this changes all ADC pins to analog inputs. It is possible to read the
|
||||
MCU temperature, VREF and VBAT without using ADCAll. The raw data can be accessed on
|
||||
ADC channels 16, 17 and 18 respectively. However appropriate scaling will need to be applied.
|
||||
.. only:: port_pyboard
|
||||
|
||||
Instantiating this changes all ADC pins to analog inputs. The raw MCU temperature,
|
||||
VREF and VBAT data can be accessed on ADC channels 16, 17 and 18 respectively.
|
||||
Appropriate scaling will need to be applied. The temperature sensor on the chip
|
||||
has poor absolute accuracy and is suitable only for detecting temperature changes.
|
||||
|
||||
The ``ADCAll`` ``read_core_vbat()`` and ``read_core_vref()`` methods read
|
||||
the backup battery voltage and the (1.21V nominal) reference voltage using the
|
||||
3.3V supply as a reference. Assuming the ``ADCAll`` object has been Instantiated with
|
||||
``adc = pyb.ADCAll(12)`` the 3.3V supply voltage may be calculated:
|
||||
|
||||
``v33 = 3.3 * 1.21 / adc.read_core_vref()``
|
||||
|
||||
If the 3.3V supply is correct the value of ``adc.read_core_vbat()`` will be
|
||||
valid. If the supply voltage can drop below 3.3V, for example in in battery
|
||||
powered systems with a discharging battery, the regulator will fail to preserve
|
||||
the 3.3V supply resulting in an incorrect reading. To produce a value which will
|
||||
remain valid under these circumstances use the following:
|
||||
|
||||
``vback = adc.read_core_vbat() * 1.21 / adc.read_core_vref()``
|
||||
|
||||
It is possible to access these values without incurring the side effects of ``ADCAll``::
|
||||
|
||||
def adcread(chan): # 16 temp 17 vbat 18 vref
|
||||
assert chan >= 16 and chan <= 18, 'Invalid ADC channel'
|
||||
start = pyb.millis()
|
||||
timeout = 100
|
||||
stm.mem32[stm.RCC + stm.RCC_APB2ENR] |= 0x100 # enable ADC1 clock.0x4100
|
||||
stm.mem32[stm.ADC1 + stm.ADC_CR2] = 1 # Turn on ADC
|
||||
stm.mem32[stm.ADC1 + stm.ADC_CR1] = 0 # 12 bit
|
||||
if chan == 17:
|
||||
stm.mem32[stm.ADC1 + stm.ADC_SMPR1] = 0x200000 # 15 cycles
|
||||
stm.mem32[stm.ADC + 4] = 1 << 23
|
||||
elif chan == 18:
|
||||
stm.mem32[stm.ADC1 + stm.ADC_SMPR1] = 0x1000000
|
||||
stm.mem32[stm.ADC + 4] = 0xc00000
|
||||
else:
|
||||
stm.mem32[stm.ADC1 + stm.ADC_SMPR1] = 0x40000
|
||||
stm.mem32[stm.ADC + 4] = 1 << 23
|
||||
stm.mem32[stm.ADC1 + stm.ADC_SQR3] = chan
|
||||
stm.mem32[stm.ADC1 + stm.ADC_CR2] = 1 | (1 << 30) | (1 << 10) # start conversion
|
||||
while not stm.mem32[stm.ADC1 + stm.ADC_SR] & 2: # wait for EOC
|
||||
if pyb.elapsed_millis(start) > timeout:
|
||||
raise OSError('ADC timout')
|
||||
data = stm.mem32[stm.ADC1 + stm.ADC_DR] # clear down EOC
|
||||
stm.mem32[stm.ADC1 + stm.ADC_CR2] = 0 # Turn off ADC
|
||||
return data
|
||||
|
||||
def v33():
|
||||
return 4096 * 1.21 / adcread(17)
|
||||
|
||||
def vbat():
|
||||
return 1.21 * 2 * adcread(18) / adcread(17) # 2:1 divider on Vbat channel
|
||||
|
||||
def vref():
|
||||
return 3.3 * adcread(17) / 4096
|
||||
|
||||
def temperature():
|
||||
return 25 + 400 * (3.3 * adcread(16) / 4096 - 0.76)
|
||||
|
||||
|
Loading…
Reference in New Issue