fredfmah
Newbie level 2
Dear Experts, I need a temperature sensor with a response time of less than 0.5 seconds.
Unfortunately the NTC thermistor is too slow for a steady reading on this time scale.
Moving on to the non-contact alternatives, I found the MLX90614 which offers two modes of operation:
Outputing the temperature as
1. a data stream SMbus or as
2. a continuous PWM
I'm using a small MCU, a PIC 18F2520 . The MELEXIS site offers an application note
"MLX90614 SMBus implementation in PIC MCU "
While this may be a great solution it means getting into a learning curve on the specific communication functions Melexis->PIC... very off puting after reading through the specific MPlab projects that are in the downloaded zip.
However there is the second mode of operation using PDF. At first sight the PIC will have three relatively simple tasks
* Calibrate the approximate 1ms to the actual value at that time
* measure the Period
* measure the Duty Cycle
But the melexis data sheet is most confusing when I try to see what is the wave form I should try and measure.
This attached diagram as far as I can see is the representation of the PWM timings.
The initial 1/8 T I can program to ignore. Then they say the PWM starts high. OK
Now in t2, which at most is 50% of T. OK
here I get lost. How do I measure T?
Any help would be appreciated.
Oh I almost forgot, How do I get into the PWM mode because the POR starts as SMbus?
Bye and many thanks
Fred
Unfortunately the NTC thermistor is too slow for a steady reading on this time scale.
Moving on to the non-contact alternatives, I found the MLX90614 which offers two modes of operation:
Outputing the temperature as
1. a data stream SMbus or as
2. a continuous PWM
I'm using a small MCU, a PIC 18F2520 . The MELEXIS site offers an application note
"MLX90614 SMBus implementation in PIC MCU "
While this may be a great solution it means getting into a learning curve on the specific communication functions Melexis->PIC... very off puting after reading through the specific MPlab projects that are in the downloaded zip.
However there is the second mode of operation using PDF. At first sight the PIC will have three relatively simple tasks
* Calibrate the approximate 1ms to the actual value at that time
* measure the Period
* measure the Duty Cycle
But the melexis data sheet is most confusing when I try to see what is the wave form I should try and measure.
This attached diagram as far as I can see is the representation of the PWM timings.
The initial 1/8 T I can program to ignore. Then they say the PWM starts high. OK
Now in t2, which at most is 50% of T. OK
here I get lost. How do I measure T?
Any help would be appreciated.
Oh I almost forgot, How do I get into the PWM mode because the POR starts as SMbus?
Bye and many thanks
Fred
