I am interested in being the battery voltage via Bluetooth to an app, so I can monitor the charge while using the app. Does anyone know how to read the input voltage on the batt pin?
Thanks
Itsy Bitsy express - reading battery voltage
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- alistair_walterhartley
- Posts: 3
- Joined: Wed Mar 09, 2022 7:00 pm
- mikeysklar
- Posts: 13946
- Joined: Mon Aug 01, 2016 8:10 pm
Re: Itsy Bitsy express - reading battery voltage
This is an example for the ItsyBitsy nRF52840 Express:
https://learn.adafruit.com/adafruit-its ... -2865012-8
https://learn.adafruit.com/adafruit-its ... -2865012-8
Code: Select all
#include <Arduino.h>
#include <Adafruit_TinyUSB.h> // for Serial
#if defined ARDUINO_NRF52840_CIRCUITPLAY
#define PIN_VBAT A8 // this is just a mock read, we'll use the light sensor, so we can run the test
#endif
uint32_t vbat_pin = PIN_VBAT; // A7 for feather nRF52832, A6 for nRF52840
#define VBAT_MV_PER_LSB (0.73242188F) // 3.0V ADC range and 12-bit ADC resolution = 3000mV/4096
#ifdef NRF52840_XXAA
#define VBAT_DIVIDER (0.5F) // 150K + 150K voltage divider on VBAT
#define VBAT_DIVIDER_COMP (2.0F) // Compensation factor for the VBAT divider
#else
#define VBAT_DIVIDER (0.71275837F) // 2M + 0.806M voltage divider on VBAT = (2M / (0.806M + 2M))
#define VBAT_DIVIDER_COMP (1.403F) // Compensation factor for the VBAT divider
#endif
#define REAL_VBAT_MV_PER_LSB (VBAT_DIVIDER_COMP * VBAT_MV_PER_LSB)
float readVBAT(void) {
float raw;
// Set the analog reference to 3.0V (default = 3.6V)
analogReference(AR_INTERNAL_3_0);
// Set the resolution to 12-bit (0..4095)
analogReadResolution(12); // Can be 8, 10, 12 or 14
// Let the ADC settle
delay(1);
// Get the raw 12-bit, 0..3000mV ADC value
raw = analogRead(vbat_pin);
// Set the ADC back to the default settings
analogReference(AR_DEFAULT);
analogReadResolution(10);
// Convert the raw value to compensated mv, taking the resistor-
// divider into account (providing the actual LIPO voltage)
// ADC range is 0..3000mV and resolution is 12-bit (0..4095)
return raw * REAL_VBAT_MV_PER_LSB;
}
uint8_t mvToPercent(float mvolts) {
if(mvolts<3300)
return 0;
if(mvolts <3600) {
mvolts -= 3300;
return mvolts/30;
}
mvolts -= 3600;
return 10 + (mvolts * 0.15F ); // thats mvolts /6.66666666
}
void setup() {
Serial.begin(115200);
while ( !Serial ) delay(10); // for nrf52840 with native usb
// Get a single ADC sample and throw it away
readVBAT();
}
void loop() {
// Get a raw ADC reading
float vbat_mv = readVBAT();
// Convert from raw mv to percentage (based on LIPO chemistry)
uint8_t vbat_per = mvToPercent(vbat_mv);
// Display the results
Serial.print("LIPO = ");
Serial.print(vbat_mv);
Serial.print(" mV (");
Serial.print(vbat_per);
Serial.println("%)");
delay(1000);
}
- alistair_walterhartley
- Posts: 3
- Joined: Wed Mar 09, 2022 7:00 pm
Re: Itsy Bitsy express - reading battery voltage
Hi, thank you. I missed this code as I have been looking for Python codes.
I will try it and see if I can convert it to Python.
I will try it and see if I can convert it to Python.
- mikeysklar
- Posts: 13946
- Joined: Mon Aug 01, 2016 8:10 pm
Re: Itsy Bitsy express - reading battery voltage
Use get_voltage() with CircuitPython to read a BAT pin.
https://learn.adafruit.com/adafruit-fea ... management
Code: Select all
# SPDX-FileCopyrightText: 2018 Kattni Rembor for Adafruit Industries
#
# SPDX-License-Identifier: MIT
import board
import analogio
vbat_voltage = analogio.AnalogIn(board.D9)
def get_voltage(pin):
return (pin.value * 3.3) / 65536 * 2
battery_voltage = get_voltage(vbat_voltage)
print("VBat voltage: {:.2f}".format(battery_voltage))
- alistair_walterhartley
- Posts: 3
- Joined: Wed Mar 09, 2022 7:00 pm
Re: Itsy Bitsy express - reading battery voltage
If I want to use UART.Write to send the voltage reading into an app, is there a specific format for example byte or string? I tried it with the variable in the brackets and get a Len() error?
- mikeysklar
- Posts: 13946
- Joined: Mon Aug 01, 2016 8:10 pm
Re: Itsy Bitsy express - reading battery voltage
Since CircuitPython 4.0, 'buf' being passed to uart.write(buf) must be in bytes.
Here is some example syntax from the UART Communication Between Two CircuitPython Boards guide.
https://learn.adafruit.com/uart-communi ... -3101783-2
Code: Select all
write(self, buf: circuitpython_typing.WriteableBuffer)→ Optional[int]
Write the buffer of bytes to the bus.
New in CircuitPython 4.0: buf must be bytes, not a string.
return
the number of bytes written
rtype
int or None
reset_input_buffer(self)→ None
Discard any unread characters in the input buffer.
Code: Select all
# Messages are of the form:
# "<TYPE,value,value,value,...>"
# We send and receive two types of messages:
#
# Message contains a light sensor value (float):
# <L,light>
#
# Message contains statuses of two buttons. Increment NeoPixel brightness by 0.1 if the second
# button is pressed, and reduce brightness by 0.1 if the first button is pressed.
# <B,btn_A,btn_B>
uart.write(bytes(f"<L,{light}>", "ascii"))
uart.write(bytes(f"<B,{btn_A.value},{btn_B.value}>", "ascii"))
Please be positive and constructive with your questions and comments.