Hi, I have a Raspberry Pico which is without any job. So I decided to do
a little project without much time.

The pico should read its temp-sensor and communicate the temp while
blinking the LED: First Figure, second figure.

23 degress (Celsius here) should be

blink blink
(pause)
blink blink blink
(wait 5 min)

Connected to a USB-Powercable the pico can tell my through camera what temperature is in my caravan. ;-)

But: How can I calculate the real room-temperature better? The results
are not very accurate.

Here is the source (public domain):

# Thermometer - get room temperature by CPU-Temperature
# and tell it users by blinking, FW 2021

import machine, time

led = machine.Pin(25, machine.Pin.OUT)

# blink - blink "times" times with duration "duration"
def blink (times, duration):
for c in range (0,times):
led.on()
time.sleep_ms(duration)
led.off()
time.sleep_ms(duration)

# Greetings: Machine okay
blink (3, 100)
time.sleep_ms(1000)

while 1:

# Get CPU-Temperature, calculate ° Celsius
sensor_temp = machine.ADC(4)
sensor_temp = sensor_temp.read_u16() * (3.3 / (65535))
sensor_temp = int (27 - (sensor_temp - 0.706)/0.001721)
zehner = int (sensor_temp / 10)
einer = sensor_temp - (zehner * 10)
einer = einer - 4 # room-temp vs. CPU-Temp

for c in range (0, 2):
blink (zehner, 250)
time.sleep_ms (1000)
blink (einer, 250)
time.sleep_ms (1000)

print ("Sensor-Temp: ", sensor_temp - 4, "° C")
print ("Zehner.....: ", zehner)
print ("Einer......: ", einer)


Thank you!

FW

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On 09/11/2021 09:26, F. W. wrote:

Hi, I have a Raspberry Pico which is without any job. So I decided to do
a little project without much time.

The pico should read its temp-sensor and communicate the temp while
blinking the LED: First Figure, second figure.

23 degress (Celsius here) should be

blink blink
(pause)
blink blink blink
(wait 5 min)

Even better with Morse Code?

In 1972 from Floor 11 of Keynes Tower at Essex Uni. I
had a small beacon flashing "HI".

Long before the days of microprocessors, discounting
the 4004, but done with reject (Plessey, I think)
RTL logic chips.

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F. W. <me@home.com> wrote:

But: How can I calculate the real room-temperature better? The results
are not very accurate.

Attach an external sensor. Either way, you'd still have to calibrate it. So that's the only way: measure the temperature in a different, known good way
and adjust the calculation accordingly.

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F. W. <me@home.com> wrote:

But: How can I calculate the real room-temperature better? The results
are not very accurate.

Often the problem with internal temperature sensors is they're affected by self-heating. If the microcontroller is running in a loop it can consume
some mA which raises its own temperature above ambient, at least until
heat-in is equilibrated with extra heat loss due to the raised temperature.

The solution to that is to go into low power suspend until the package has matched ambient temperature. Then take a measurement as the first thing you do, transmit it, and go back to sleep.

In your code you could try longer sleep() periods between readings, but
you'd have to check if that actually causes the device to go into suspend,
or just spins in a loop. The other approach is to set a timer interrupt for some time hence and then 'Wait For Interrupt' (WFI instruction) which should enter CPU power saving mode. Although you might also need to consider
whether any peripherals are also taking power.

As has been mentioned, using an external temperature sensor that's not right next to the MCU or other heat generating components avoids this problem.

Theo

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In message <smderr$9a3$1@dont-email.me>
"F. W." <me@home.com> wrote:

Hi, I have a Raspberry Pico which is without any job. So I decided to do a little project without much time.

The pico should read its temp-sensor and communicate the temp while
blinking the LED: First Figure, second figure.

23 degress (Celsius here) should be

blink blink (pause) blink blink blink (wait 5 min)

Connected to a USB-Powercable the pico can tell my through camera what temperature is in my caravan. ;-)

But: How can I calculate the real room-temperature better? The results are not very accurate.

I solved this problem some years ago by buying a Sensirion temperature
and humidity sensor, which is factory calibrated. It communicates via
IIC.

May not be the sort of solution you want, of course! It depends on how
much accuracy you need.

David

--- SoupGate-Win32 v1.05
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On 09/11/2021 09:26, F. W. wrote:

Hi, I have a Raspberry Pico which is without any job. So I decided to do
a little project without much time.

The pico should read its temp-sensor and communicate the temp while
blinking the LED: First Figure, second figure.

But: How can I calculate the real room-temperature better? The results
are not very accurate.

There are a number of cheap temperature sensors which you can connect
via Pico's I2C pins, and will be far more accurate than the sensor in
the chip package, which will be affected by the load on the CPU.

I use htu21df or si7021 for temperature and humidity, and BME280 for temperature, humidity and pressure.

Blinking lights are a start, but why not hook up either some 7 segment
LEDs, or tiny LCD display to the Pico's output pins.

---druck

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