Temperature sensor

shashank.tilwalli · December 14, 2018, 11:42pm

Hello experts,
I am trying to run grove_temperature_sensor from the given sample scripts. When I open the py file, I see as per instructions it is asking me to connect to analog port A0.

When I run it, I get following output

('temp =', 256.829434239294)
('temp =', 256.829434239294)
('temp =', 307.829434239294)....

line 246 error.

Value Error: math domain error

Any pointers? What is the expected value.

RobertLucian · December 17, 2018, 8:23am

Hi @shashank.tilwalli,

That should be caused by some arithmetic calculation that doesn’t make any sense, mathematically speaking.

Hmm, there should be something coming from that log. Can you place some prints in the following function and see what the output is?

github.com

DexterInd/GrovePi/blob/master/Software/Python/grovepi.py#L237-L248


def temp(pin, model = '1.0'):
	# each of the sensor revisions use different thermistors, each with their own B value constant
	if model == '1.2':
		bValue = 4250  # sensor v1.2 uses thermistor ??? (assuming NCP18WF104F03RC until SeeedStudio clarifies)
	elif model == '1.1':
		bValue = 4250  # sensor v1.1 uses thermistor NCP18WF104F03RC
	else:
		bValue = 3975  # sensor v1.0 uses thermistor TTC3A103*39H
	a = analogRead(pin)
	resistance = (float)(1023 - a) * 10000 / a
	t = (float)(1 / (math.log(resistance / 10000) / bValue + 1 / 298.15) - 273.15)
	return t

Thank you!