The most common analog input for any control and measurement system is temperature and the most common (and least expensive) temperature sensor is the thermistor. The Pi-SPi-8AI is now offered as an 8 channel thermistor temperature sensor interface.
The kit includes everything required to get going with temperature measurements:
- 8 channels configured for thermistor inputs
- 40 pin to 26 pin cable to connect to the Raspberry Pi
- Qty 1 10K 3380 Beta Thermistor with 36" of lead length (Cantherm)
- Qty 3 10K 3380 Beta Thermistors (Cantherm)
The input circuits are all pre-configured and are ready to go! Each input circuit looks like this:
The test code provided uses the Stein-hart Equation for simple, reliable and accurate temperature readings.
Here is part of the test code that shows how the equation works:
// Steinhar-Hart Equation Defines for 10K Thermistor Beta 3380 Temp Sensor
#define R_LOAD 10000.0
#define R_ROOM_TEMP 10000.0 // for 25 Deg C
#define T_BETA 3380
#define T_AD_COUNTS 4095 // MCP3208 is 12 bit ADC
#define ROOM_TEMP_NOM 25.0
void Update_Temperatures(unsigned char channel) {
float sample;
unsigned int average;
int i;
// Calculate Temperature for Cold Water Line
average = 0;
for(i=0; i<5; i++) { // take 5 reading and average
Update_Analog(channel); // to smooth out the reading
average += AN_AD[channel];
}
average = average / 5;
sample = ((float)T_AD_COUNTS / average) - 1;
sample = (float)R_LOAD / sample;
sample = sample / (float)R_ROOM_TEMP;
sample = log(sample);
sample /= (float)T_BETA;
sample += 1.0 / ((float)ROOM_TEMP_NOM +275.15);
sample = 1.0 / sample;
sample -= 273.15;
AN_Temp[channel] = sample;
}
Applications for this interface would include:
- HVAC Controls
- Hydroponics
- Refrigeration (Fridge/Freezer) Temperature Monitoring
The Pi-SPi-8AI Temperature Sensor Kit can be purchased here.